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Hi. I have a question. Do substances(for example Fe or Benzene ) in trace amounts (for example micrograms per liter) cause light refraction? and if they do, is this refraction large enough to be detected? and also if they do, is this refraction unique for each substance?
I also need to know if we have a solution with different substances, can refraction help us determine what the substances are? can it measure the concentration?
Thanks for your help
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It is also on ResearchGate. Author Shangli Pu. Measurement of refractive index of magnetic fluid by Retro - reflection on fiber optics end face.
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I have profiled a collimated pulsed laser beam (5mm) at different pulse energies by delaying the Q-switch and I found the profile to be approximately gaussian. Now I have placed a negative meniscus lens to diverge the beam and I put a surface when the beam spot size is 7 mm. Should the final beam profile (at the spot size = 7 mm) be still gaussian? Or the negative lens will change the gaussian profile? Is there any way to calculate the intensity profile theoretically, without again doing the beam profiling by methods like Razor blade method? Thanks.
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Gaussian laser beams propagate as gaussian laser beam if their intensity is sufficiently weak so that they do not affect the refractive index of the medium through which they propagate and a linear approximation is valid. Furthermore the
"diameter" of the laser beam should be large compared to the wavelength so that a Fresnel approximation is valid (at least a few micrometers). Also the medium should be (fairly) homogeneous. This is related to the paraxial approximation used (small angles of deflection). The formulas for gaussian beam propagation a easily found in various textbooks. There is no fundamental difference between divergent and convergent lenses. The standard paraxial matrix formulation used in geometrical optics can be used to calculate gaussian beams transformation. The beam is characterized by its "waist diameter Wo" and the position of this waist "xo" with respect to the lens.
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The figure attached here shows the electronic band structure of TiO2. Projected onto the band structure the weights of electronic orbitals. Such a representation helps us visualize the orbital content of bands a given energy range. In the figure, pink, blue and green colors are the projection of Oxygen px, py and pz orbitals, respectively, on to the valence bands. Similarly, for conduction band, red, orange and brown colors represent projections (weights) of Titanium 3d-xy, 3d-yz+3d-xz , and 3d-eg orbitals.
Considering the band structure, the optical gap(direct) comes along the Gamma-Z direction in the Irreducible Brillouin zone. Given this information and projected band structure in the Gamma-Z region, how one can deduce the selection rules for optical transitions?
How can one say for which polarization of incident light the first band gap excitation occurs? What happens when other polarization are used? What are the selection rules governing the phenomena?
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Adding to the colleagues above, the most favorable transitions are those transitions that satisfy the conservation of energy and momentum of the incident photon and the valence electron. That is the sum of the energy of the energy and momentum before the collection is equal with those after collision.
Since the photo momentum is negligibly small, then the favorable transitions are those of the direct band transition.
The transition of electrons are such that when it is transferred from an orbital with energy E1 and momentum M1 to an orbital with energy E2 and momentum M2 it must given the difference in the energy and in the momentum. So since the photon can not change its momentum so it will be transferred to na orbital with same momentum but with an energy= E1+Eph where Eph is the photon energy.
Best wishes
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BER analyzer parameters meaning.
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The reliability of data transmission characterizes the probability of getting a distortion for the transmitted data bit. This indicator is often referred to as the Bit Error Rate (BER). The BER value for communication channels without additional means of error protection is 10-4 — 10-6, in optical fiber — 10-9. A ber value of 10-4 indicates that on average, one bit is distorted out of 10,000 bits. The q-factor of the receiving system Q is determined from the expression:
Q = GA/TC,
or, in logarithmic form:
Q[dB] = GA[dB] - 10lgTC[x].
It is the q-factor of the receiving system that determines the signal-to-noise ratio (C/N) at the output of the low-noise Converter (LNC or LNB). It is important to note that the final C/N value does not depend on the LNC gain.
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When simulating light pipes, will the choice of a source (collimated beam vs angular beam) make any difference on the efficiency of the light pipe to channel light from source on one end to the detector on the other end.
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Hello Avijit Prakash,
Based on my knowledge, the radiation pattern of your light source has a significant effect on your results. Therefore, I strongly agree with Dr. Sascha
Regards. - Hossien
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How can i check that the Circular polarized beam is Right-handed or Left-handed? I use a Quarter-wave plate to make the circular polarized beam. I don't mind any method.
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Maybe you can use Jones Matrix to do the algebra.
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The energy density was calculated using this formula, Energy Density = E/A (J/cm2). Here E is the input energy measured in millijoules, A is the area of the circular spot.
E values I know from LDT analysis.
A value, How to calculate using the following parameters?
Laser Beam diameter= 8 mm
Focal length = 20 cm
Nd:YAG laser = 1064 nm
Pulse width = 10 ns
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Time duration of laser pulse is needed if one need to calculate the Laser intensity. This can be obtained by dividing the energy density by the time duration of laser. It will have unit of W/cm2.
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I'm looking for the formula of periodic metallic nanoring arrays' resonance position. I've searched for plenty of literature with no results. Does anyone have profound physics background and familiar with this? Thanks so much!
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Xueyao Liu , to my knowledge there is no an analytical expression for the resonance frequency of a metallic ring, let alone an array of those, because this is not an analytically solvable problem. But try to look at Garcia de Abajo's review on arrays ( ), you might find useful information there.
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Just curious, can someone please show me how does look like the grating pattern of the "axicon" to generate a lattice light-sheet? A picture or general scheme will be greatly appreciated:)
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Hi, Aaron
"Spatial light modulator" — that's the correct name of the element I was looking for;)
Quite interesting device and seemingly can be produced by photolithography.
It should look like some of these:
Was wondering about the purpose of the annulus, but could find about it on the original Betzig's paper (doi:10.1126/science.1257998)
Thank you!
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I'm trying to draw an optical diagram for my setup, I prefer 3D program.
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I think the solidworks program is easy and useful to use in free drawing for the optical diagram in 2D or 3D . in addition to the 3Dmax.
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I prepared ZnO via a different method but I found something. I think it's a strange optical band gap.
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If you confirmed the formation of ZnO by different experimental tools and you found a decrease in the band gap relative to bulk Zno structure, then, the decrease in the band gap may arise from the formation of crystal defects like oxygen vacancies. You could confirm this interpretation by measuring the fluorescence spectroscopy.
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What is the best way one can measure the refractive index of different concentration for the same solution, i.e. silver nitrate AgNO3 in de-ionised water? Silver nitrate AgNo3 in different concentration, i.e. 100mg/l or 50mg/l.
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Not of direct help to the question asked, but I offer:
Langford, S. A., and J. K. Nakagawa, 1978. A general equation for estimating refractive indices of Cargille liquids at various temperatures and wavelengths. The Microscope, v. 26, no. 4, pp. 167 - 170.
&
Langford, S. A., 1991. A modified Jelley refractometer. The Royal Microscopical Society J. Microscopy, v. 163, pt. 3, September, pp. 333 - 345. [Please note that the equation on p. 339 requires addition of constant 1.517207, which was inadvertently lost due to an interruption during my final editing work. The correction was published in a later issue, which I can not locate on the Web. --SL, 20 Oct 2016] https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-2818.1991.tb03184.x, tinyurl.com/ya9ahlc8.
For purposes of liquid-immersion refractometry [see, for instance, < https://tinyurl.com/yabku63f >] I think that there is no substitute for calibration of liquids soon before they are to be used. Better yet would be the development of an instrument that would continuously log Liquid RIs during liquid-immersion work.
I hope that these thoughts help at least some readers. :-)
-Steve-
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When an electrode made of semiconductor nanotubes/nanowires etc is illuminated an overshoot or transient maximum in the photocurrent is observed. The photocurrent gradually exponentially decreases from the transient maximum and gets saturated after some time. 
However, there are also some cases, where the photocurrent keeps increasing instead of decreasing. Why does this increment happen? What is the proper reason behind this? Please explain with proper references.
Thanks in advance.
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I had asked this question two years ago. Fortunately, Last year we published a paper trying addressing this issue. I request all of you who are reading this question, to read that article and let me know your valuable comment.
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I have x ar ray tube and I want to calculate Solid angle of radiation from x ray tube, but how??
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Just divide the area of (perpendicular) illumination by the square of the distance (to x-ray focus) .
Solid angle omega= area/distance².
The type of 'area' depends on what you are looking for.
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What additional information does the phase measurement in a frequency-domain imaging technique provide compared with the continuous wave technique that measures only the amplitude of the diffuse light?
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A phase shift of a frequency modulated light source is almost equivalent to a change in mean flight time of the photons and hence provides information about the mean free path length of the photons through the tissue. This information is distinct to that provided by a change in amplitude, which is the only variable measured in continuous wave (CW), and helps in distinguishing the degree to which attenuation is a result of either scattering or absorption events. In certain cases, such as diffuse optical tomography, it is possible to separate scattering and absorption using CW measurements by solving a regularised inverse problem, however frequency domain measurements will typically improve this separation by reducing the non-uniqueness.
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Dear All,
Your input will be helpful for me over this topic.
I am trying to understand if there is really a relation of direct energy gap with thermo-optic coefficient (TOC) and if this physics is true.
If we consider following material example,
SiO2, its direct Eg=11 eV while low TOC = 1e-5 /C
on other hand, Si has direct Eg = 3.7 eV, TOC = 1.8e-4 /C,
will it be physically (i mean in physics) correct to give this argument?
I look forward to your expert input.
Thank you...
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good answers ...following answers
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Dr E M Wright
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Thanks respected Ali Farmani,
thanks for valuable suggestion, my mail is arvindsharma230771@gmail.com please send your mail for queries.
Is their some possibilities in other carbon material like graphene.
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For Nonlinear optical phenomena and materials that are used in the field of nonlinear optical
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Dear Dr. Ali Benghia
I suggest you book Physics of Nonlinear Optics, Guangsheng He, Song H. Liu-World Scientific
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In grazing incidence optics, COMA gets eliminated if optics has an even number of reflections and not for an odd number of reflection. I tried with ray tracing simulations from 1-4 reflections. Can anyone help to understand analytically? 
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Hi Panini, in the publication that you kindly cited, "Optics for X-ray telescopes: analytical treatment of the off-axis effective area of mirrors in optical modules", appendix B, p.12, you can find an analytical approach to your question. The treatment is approximate and  was hitherto developed only for 1 and 2 reflections, but you might like to extend it to an arbitrary number of reflections, if you feel inspired at this. In case, let me know...!
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Dear researchers,
I am using a light source (UV) to irradiate my sample (sample diameter = 0.5 cm). It is difficult to measure the surface temperature using infrared thermometer since effective diameter area should be more than 3 cm. If you know how to calculate the surface temperature or any paper describes about it, please let me know.
Thank you very much.
Best regards.
Singgih W.
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Use thermistors close to the sample. They come in various shapes and sizes. Some have holes in the middle (e.g. <http://www.chipkin.com/thermistors/>), so your sampling could be done above and in the middle of one, which will act as a black body and irradiate your sample with an essentially constant temperature, if controlled via a Wheatstone Bridge and a stepped-decade resistor box. Do your own calibrations.
I hope this helps, Singgih. -Steve-
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I would like to know the different modes supported in an optical fiber with an hexagonal geometry. Do this excited modes depend on polarisation?
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Dear Ali, exact/approximate analytical solution is not available for Hexagonal waveguide. You can get some idea on hexagonal modes from J. Helszajn's work on equilateral resonator/circulator etc. The work by C H Papas on different waveguide (1956) may help you to get some idea. But these are nor complete solutions. We have work on it to find exact analytical solution as found for rectangular / circular / elliptical / annular and equilateral, 30-60-90 and 45-45-90 shaped triangular waveguide.
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If a non-absorbing film is put on a perfect electric conductor the reflectivity of the system is still unity. In case of real metals, interference effects become obvious through interference fringes in the reflection spectra. Since transmittance is zero in these systems, this means that absorption takes place.
In fact, this is known and these systems have been used for a long time e.g. as as high-temperature solar absorbers.
What I could not find in the corresponding literature is any hint on the microscopic nature of the absorption. It could take place in the metal due to a non-zero skin depth, but normally light cannot couple to bulk plasmons at the surface of a metal as the corresponding dispersion relation does not cross the light line. The excitation of a surface plasmon could be possible, but still light has to be coupled in. Since you also find the effect above for normal incidence it can not be a kind of prism coupling etc. Probably I miss something very basic, but what is it that is excited by this absorption and how is the energy converted to heat?
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Dear Thomas,
in my opinon, the following scenario shold be drawn here: The (perfecly nonanbsorbingt) dielectric film on the metal can act as (imperfect) antireflection coatiing: in backreflection, direction: the ligt refelcted from the air/dielectric interface superimoses with the ligh reflected from the dielectric/metal interface. (the first reflecion is weak, the second one is strong). If the coherence length of the light is larger than the optical path difference between both partial beams, they can interfere. For certain dielectric film thinknesses this can occur constructively (leading to a maximum in backreflection) for some other film thicknesses the beams are interfering destructively (leading to a minimum in backreflection). In the latter case, more radiation will be absorbed by the metal film (skin depth is not relevant here). Since one partial refelction is very strong here and the other one is very weak, the modulation effect is not very strong. Plasmon excitation in the metal/dielectric interface, or any absorption in the diielectric film is not required for having such effects.
Hope this helps,
Best regards, Jörn Bonse
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How do you explain the BeamSplitter-evolution of a coherent state with an unknown polarization state that leads to cloning its unknown polarization state?(see attached image for details)
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Hello there,
Why is this considered as a violation of no-cloning theorem? Coherent state is not a single photon state, and what you do with a beam-splitter is just dividing  the number of photons in half at each port. The cloning definition is different; copying information onto another particle (having two identical particles). In your case, you have many copies and just devide them into two
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I want to measure the retardance and diattenuation for a set of retarders and polarizer at visible wavelenghts. I would like to know what are the methods and devices to measure those properties.
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Uygun Vakhidovich Valiev · 30.62 · National University of Uzbekistan
I believe that you can use the following method for the measuring of phase light shift described by Randall D.D.: "A new photoelectrical method for the calibration of retardation plates", JOSA, V. 44, No 8, P. 600-602 (1954).  It is very successful and enough simplest experimental method....
Hope it helps!
2h ago
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I have removed Fresnel lens from rear projection TV but it is plane/smooth/without grooves/without Newton rings. It concentrate the solar radiations to some extent. The Fresnel lens with grooves is more effective to concentrate the solar radiations. I am interested to convert it into grooves. I hope that the audience can help me in this regards.
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Thanks dear U. Dreher
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I generate orthogonal spatial modes like Hermite-Gaussian or Laguerre-gaussian from two different laser sources. Thus coming from incoherent sources will they not be orthogonal? Or in other words does having a phase difference affect the orthogonality of these modes?
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No.
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if in chromatic confocal sensor, a led with low coherence and a multi-mode fiber are used. I wonder this imaging process should be the which one ? In the monograph about fiber optical confocal scanning microscopy by GuMin, he treat the imaging process as totally coherent imaging when a laser and single-mode fiber is used.
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:-) Enjoy your work, Cheng Chen. -Steve-
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I have an autocorrelation setup, which we observed field correlation with quite high visibility. Then, I insert the BBO crystal which converts 990nm to 475nm. I inserted a aspherical convex lens that focus light onto the BBO crystal and a lens to collimate the light onto a detector. The light that enters BBO come from two arms, one arm has a variable path delay. The power I apply is 5mW, with pico-second duration pulse, 13ns repetition rate. I also put a black cardboard in front of BBO to measure its back reflection, so that I have achieved phase matching condition.
However, nothing is observed so far. The reason why I think this is hard because SHG is not even measurable, and we can't optimise it without observing it at the first place. Can anyone suggest what could go wrong in such a set up? Why is there no SHG?
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Given your specifications of ~1ps 5mW (cw averaged) and 76MHz rep rate you have quite little pulse energy / intensity.*
For a common beam diameter of about 800µm you will need a f=+100 to f=+200mm lens and a ~5-10mm long BBO crystal to get a few µW of SHG. (Adjust the rayleigh length to the length of your BBO).
If you focus harder you will gain in efficiency by the higher intensity but loose effective length by spatial walkoff. If you havent you could take a day or two to download the free program SNLO (I am not the author) and simulate your process in 2D SP MIX to optimize the relevant quantities.
There are also a lot of good books on nonlinear optics. Given your plan to set up an autocorrelator I would recommend Rick Trebinos's book on Frequency Resolved Optical Gating wich also has a nice primer on nonlinear optics and also is a very good basement for interpreting autocorrelation traces.
Please be aware that even if you know the cut, the error margins on the cut angle are big enough to prevent phase matching for BBOs that are longer than a few hundred µm. So you WILL have to optimize the angle. The polarization sould of course be adjusted first.
If you do not have any clue about the cut of your BBO it might be helpful to request about 100mW of the Oscillator for a day and caracterize the BBO first. The cyan spot of ~1µW SHG will be barely visible when you adjust the SHG for the first time. It also helps to prealign the device with more power first and then reduce it to the desired SNR.
Please apologize the lack of quotations for my statements, I had only very limited time for this answer.
PS: It is always helpful to state all relevant physical quantities as for example beam diameter, focal length etc.
* It is also possible to get high efficiency SHG with ps-pulses but in my experience only if you start with 10+µJ or use a resonator. Keep in mind that you anyway do NOT want to drive the efficiency in saturation for a pulse measurement device.
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This is used for image reconstruction.  Another thing about the modulation of diffuser either it is phase or amplitude or both?
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@Khaled, I am really thankful to you. This would help me to reconstruct my images.
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Hi All,
Can graphene reflect visible light just like mirror? Thanks.
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Dear Md Shamiul Fahad, 
In measuring the amount of light that was reflected back, recent researches found it there is a reflection of a particular pulse. More specifically, the material's optical gain property occurs because as the pump laser pulse strikes the graphene, its electrons become excited with more charge carriers winding up in the Dirac cone than in the lower cone.
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Wavelength-dependent values for the complex index of refraction of many materials are available in the literature.
However, temperature-dependent values seem to be quite scarce.
Any clues to where I can get spectral temperature-dependent values of the complex index of refraction for water and aluminum?
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I'm looking for an optical material (preferably, glass, but would consider organics) that has a reasonably flat transmission spectrum spanning from approximately 400 nm to 2000 nm, and does not transmit above that wavelength.
BK7 (and most other soda-lime optical glasses) transmit up to at least 2.5 microns. Hot / cold mirrors and short-pass interference filters never seem to extend far enough (the closest thing I found was the extended hot mirror from Edmund, with a window from 750 nm to 1750 nm). KG type glasses from Schott are alright on the blue side, but don't transmit far enough (cutting out at about 1000 nm).
Is there a common optical material I'm missing?
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A homogenous material might be impossible to find, since you always fight with vibrational absorptions, be at fundamentals or higer harmonics and combination bands. A way to go would be to take a material that transmits far into the infrared and apply a thin metamaterial layer which acts like an effective metal above 2000 nm.
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What happens when electromagnetic wave (EM) incidents on a metal plate? Does it reflect back? If yes then how to calculate how much (percentage) is reflected back. Kindly suggest any mathematical formula to calculate the reflected to incident wave ratio, when EM-wave travel from dielectric medium and incidents on a metal plane.
Your suggestion(s) will be highly helpful. 
Thank you.
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hi
you should read the advanced elwctromagnetic book of balanis, chapter 5 i think. in this chapter, this is explaned very good. i sugest you, read this chapter. it is complate. and every thing is discused.
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I'm working on a pump probe setup with one focusing lens for both beams. So the spot size of the pump and the probe would be the same. I'm looking for a way to reduce the probe spot size. (probably using a second lens for the probe beam). Is there any easier way to reduce the spot size?
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Hi Saeed,
you can discover your possibilities if you analyze the parameters affecting the spot size of a focused laser beam. For example in the book of W.M. Steen „Laser Materials Processing“,Springer Verlag, 1991, you can find the approximation
Focus-diameter(Gaussian beam)=2w0~(4*lambda*f)/(pi*D),
where
lambda= wavelength
f= focal length
D= beam diameter at focusing lens
This formula indicates several options for reducing the probe beam spot size:
(i) Reduce the focal length (f) of the probe beam lens [requires larger changes to your setup]
(ii) Increase the beam diameter D on the last probe beam focusing  lens (as already suggested, note the scaling with 1/D and check the magnitute of the effect for your lens), This can be done by an beam expanding telescope in front of the probe beam focusing lens. Choose the telescope type carefully if you are using ultrashort laser pulses and keep in mind that it may prolongate the temporal resolution (probe beam duration in the focus)..
(iii) Reduce the probe beam wavelength (lambda); this may be done by frequency-doubling in a nonlinear crystal (in case of laser pulses and sufficient intensity) [requires larger changes to your setup].
Note: You should NOT use a pinhole(aperture) in the probe beam, since for small aperture sizes diffraction effects increase the beam sopt size in the focus (See the excellent text book of A.E. Siegman on "Lasers"). However, if you have enough energy/intersity in the pump-beam, you may add such an aperture in front of the pump beam focusing lens in order to use the diffraction effect and make the pump-beam spot size somewhat bigger (compared to the probe beam).
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The focal length of the lens required to couple light into a common fiber (want same gaussian spot size) at 633nm is larger or smaller than the one required at 980nm?
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The fundamental mode of an ideal (infinite) parabolic fibre is Gaussian, and this remains a reasonable approximation for a parabolic graded index fibre supporting many modes.
Mode field diameter is approximately d = 2 a sqrt( 2 / V )
Where again a is the core radius and the fibre numerical aperture is determined by the refractive indices of core and cladding 
NA = sqrt( nco2 - ncl2 )
So the mode field diameter is roughly proportional to the square root of the wavelength.  In a 50 micron core 0.21 NA parabolic graded index fibre, the fundamental mode field diameter at 980 nm is roughly 12 microns.  Expect a slightly larger diameter if there is a small refractive index dip or flattening in the centre of the core.
To match the mode field diameter using a 9 mm focal length lens, the collimated beam diameter at 980 nm should be D = 4 f wavelength / (pi d) = 0.94 mm.
At 633 nm, 1/e2 beam diameter roughly 0.74 mm would be appropriate, using the same lens and fibre.
Moderate degrees of coupling mismatch will excite a proportion of higher order modes.  Is this acceptable?
For an infinite parabolic profile, the scalar wave solutions have field distributions which are the product of a Gaussian and a generalised Laguerre polynomial, and this will be a reasonable approximations for modes sufficiently far from cut-off.
Too small or too large a launch spot will excite radiation modes, degrading the coupling efficiency.  However, beam diameters between 0.4 and 2 mm should couple most of the light into guided modes for the fibre in my example.
Allan W. Snyder & J. D. Love, “Optical Waveguide Theory”, Chapman Hall, 1983, ISBN 0 412 09950 0.
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LCDs require 2 polarisers.  But OLED should not need one. However I have seen some sketches where a polarizer is present. Why?
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Indeed it is related to reflections. Every pixel (actually color subpixel) of an Active Matrix OLED (AMOLED) is made of a TFT transistor, a cathode and an emissive layer. It is customary to include a mirror layer under the TFT to enhance emission on the output direction. This setup has a problem: light coming from outside can get into the device, go through all the layers and be reflected by the mirror. This reduces dramatically the contrast. Placing a CIRCULAR polarizer on top (actually, a linear polarizer plus a quarter wave plate), the ambient light becomes circularly polarized inside the device, e.g. right-handed. The mirror inverts the handiness i.e., from right-handed to left-handed upon reflection. Then reflected light is then cut off by the top circular polarizer.
Summarizing, using a circular polarizer in OLEDs you lose brightness but increase significantly contrast.
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Dear optics experts,
Recently, my colleague says that the colored band around the objective lens can regard as the location of the back focal plane. 
Do you think it is reasonable? 
Or, is there another rule of thumb to find the position of back focal plane of objective lens?
Regards,
**
Added :
Sorry for did not contains full information.
I already know that color means the range of the objective lens' magnification. 
As you already know, the objective lens is not a singlet, and back focal plane is sometimes located in the inside of objective lens barrel. that's why I am trying to find the rule of thumb. 
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Hello Yong,
as far as i know, the colored line is not supposed to indicate the plane of the objective back aperture, or at least i did not find confirmation anywhere.
You can measure the position of the back aperture if you have some simple optics tools, following this procedure:
- Mount the objective horizontally on the table
- Shine a low power, visible, collimated coherent light source in the objective from the sample side (a laser pointer is ok-ish if you don't have a proper laser).
-mount a vertical flat surface on the back of the objective, and measure the diameter of the beam and the distance of the surface from the objective. Repeat the measurement for several distances
- The diameter of the beam should increase linearly, if you interpolate and find the position at which your diameter would be 0, that is the back aperture position of the objective.
In alternative, if the manufacturer specifies the maximum field of view of the objective, you can try to have a rough estimate from the objective specifications, by just measuring the diameter of the physical aperture at the back of the objective. In this case:
- compute the focal f of the objective, which is the focal of the microscope tube lens divided by the magnification of the objective
- compute the angular field of view, as tan(θ)=FOV/(2*f), where FOV is the field of view of the objective
- estimate the back aperture diameter as d=2*f*NA/n, where NA is the numerical aperture of the objective, and n is the refractive index of the immersion media
- Measure with a caliper the diameter D of the last accessible aperture of the objective, it should be slightly bigger than d
- At this point the distance of the back aperture plane from the physical back of the objective should be (D-d)/(2*tan(θ)) 
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I'm taking the ratio of the CBS signal intensity to the diffuse background intensity for my CBS analysis and I find that the ratio (enhancement factor is around 1.4 to 1.6 and not 2 or above). I'm collecting the CBS signal in source polarization direction and the diffuse background with orthogonal polarization. What may be the possible causes for less enhancement factor? Is anything wrong with my analysis procedure?
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Out of the diffuse background in CBS experiment. Scattering amplitude at zero degree and 180 degree are equal hence, at CBS cone maxima should occur at 2. It will be better to normalize diffuse back ground at 1 and measure intensity of backscattered cone. I hope it will help you. 
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I have obtained psi and del values for different wavelengths for 3 different angles (VASE data).
How do I calculate refractive index using this data. 
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Ellipsometry is an indirect technic. As consequence, a physical model is necessary to reproduce the sample composition. In addition, a fitting for thickness, volume fraction and dispersion law parameters, corresponding to each composition, to reproduce the experimental measurment (psi and delta or Is and Ic).
I noticed you to read this two references :
1. R.M.A. Azzam, N.M. Bashara, Ellipsometry and Polarized Light, North-Holland,
Amsterdam, 1977.
2.M.-B. Bouzourâa, A. En Naciri and All., Materials Chemistry and Physics 175 (2016) 233-240.
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Thanks to all for response, may someone send me the book  Optical Solitons by Agrawal and Kivshar.
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During the building up a free space Optical Coherence Tomography system, we normally want to align the beam splitter cube as perpendicular to the incoming light direction as possible, because it will make the alignment of the reflected back easier to align and then easier to couple into fiber of the detection part. However, when this beam splitter cube is very perpendicular to the light, there will be light leaking out through the fourth surface. When you block the trans-through surface and the reflect surface, there is still detectable light on the fourth surface, and this amount of light is causing noticeable noise in the interfere fringes. Is there better method to use during the align of a free space OCT system? 
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One way that worked for me in with more or less similar problem was to put quartet wave plate on the path of interest. Upon incidence and reflection, the beam is pathing the plate twice so has it polarization rotated by 90 degrees. So you could use a polarizer to filter  out the reflection from optical surfaces. 
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Hi, i'm looking for a tool that will enable my to draw good sketches for my article. Most of the sketches will be optical systems, light rays through lens etc.
Can you please recommend me.
Thanks.
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Why does dipole moment of water molecule and polarizing effect produced by hydroxyl (OH) group saturate the polarizability of surrounding atoms in response to a light wave field? So the non linear optical susceptibility is decreased in this case. 
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Thanks for your response Sir. But i am confused about the statement that ''Apparently, all the fault pairs C2H5OH'' . Kindly can you explain it for me so i can get the exact information.
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I am trying to perform mode analysis of a photonic crystal fiber (PCF) using COMSOL multiphysics, which basically gives the effective indices of the modes as output. 
As I get two linearly polarized modes at 90 degrees with each other, is there any way to tell which one is the fast/slow axis mode by just looking at the effective index values ? 
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Fast/slow axis in the context of optical birefringence refers to the difference in phase velocity between the two modes.  It follows that the slow axis corresponds to the mode with the higher effective index. 
Phase velocity = c/neff, where c is the free space velocity of light.
If you are interested in the group delay for pulsed or modulated signals, then you need the group velocity which depends on the rate of change of effective index with wavelength.
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Hi! Due to symmetry the piezo-optic tensor is represented as a 36 components matrix. Moreover and depending on the crystal structure most of this components are 0 or symmetric. In the case of the alfa-BBO ( 3m structure) this can be represented as (see image), and for the YAG (m3m), see image.
 How can I find this symmetries and values for the piezo-optic tensor for  structures  as beta-BBO (R3c), or in general other laser crystal structures?
References: J.D.Foster. "Thermal Effects in a Nd:YAG Laser"
Y.Vasylkiv "On determination of sign of the piezo-optic coefficients using torsion method"
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I found the answer @Physical Properties of Crystals - J.F. Nye.
Pg: 141 and 251
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 Thanks for Qiu and Huang , with theoretical aspects are main emphasis but these kinds of experimental results are also helpfull for me.
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A Gaussian beam is guided through a Single mode fiber. But if we propagate a Bessel beam through a Single mode fiber, then will it guide the Bessel beam like Gaussian beam? that means will the Bessel beam show the same guiding property in the conventional single mode fiber like Gaussian beam?
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A conventional single mode fibre will not support a Bessel beam.
The fundamental mode typically has a field profile which is similar to, but not precisely Gaussian.  A Bessel beam has multiple annular rings with alternating phase reversals.  Attempting to couple light from a Bessel beam will excite higher order modes.  In a single mode fibre, these will be radiation modes, which are not supported - this is what we mean by "single mode".
Once the radiation modes have dissipated or been absorbed in the fibre coating, the output from the fibre will be approximately Gaussian.  Note that the mode field diameter and the rate of divergence will depend only on the fibre properties and the wavelength, not on the input field distribution.
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Behind the biological material in interaction of logical material, it assumed that acoustic-optics, biophonon formation etc can be responsible for many mysterious phenomenon by/along human mind & body interaction with environment as well.
Logic based entities have another aspect which get highlight in further deep down insight. That’s Shadow Formation. In previous question it’s tried to figure out that what can be different structural & functional aspect in term of mechanism behind shadow formation. Now its specific focus on expected functional matrix of Light & Shadow with reference to be use in any technology other than usual photography. As an outcome of last question is telling that subatomic particle can form shadow. And from ascent eras the role of shadow formation in Eclipse is also in common observation. However both are different phenomenon. Here the question is that why natural systems at cosmos produce shadow and make its link with biological entities. What’s further in to it?
There are two kind of object,
1.      One who emit light and one who don’t emit.
2.      Those who don’t emit light either reflect the light, pass it on or absorbed it.
Common observation is that shadow get formed against those objects which reflect light by some outer light source (after crossing the light from object). When some time we can see the shadow of bulb, tube light as well if near to more intensive light source. Sometimes human senses recognize many thing in darkness as shadow as well, still or moving. So such common observation give hint that technology formation regarding shadow sciences can possible. Shadow is much more than we ever think, the light-Shadow Matrix is just one aspect, which might include Energy Control, Light & Darkness intensity Control, Parallel / Mirror Movements etc. Might be shadow also give us the hint of formation of Minimum Possible Compact Structure (MPCS) as well
Here are few more questions with aim to go deep and find some clue for Light & Shadow Matrix
1.      What can be different aspects of Light-Shadow Matrix?
2.      Shadow formation can only occur in presence of light or other natural entities can form shadow as well?
3.      What can be Acoustic-Optics Shadow? Is there are relation of acoustic-optics with shadow, can sound mix with light form shadow?
4.      Can shadow move with the same speed as the object move for which shadow is getting form?
5.      What can be Mirror-Shadow?
6.      Do shadow can have same properties as light have but in opposite/ mirror direction?
7.      What is real insight of Subatomic Shadow Matrix & Effects (SSME)?
8.      Can a shadow escape from Light Absorbing Objects like Black Holes?
9.      How can we take shadow under experiments to go deep inside into different structural and functional aspects with reference to technology making?
10.   Any other point you want to add
A further addition that any research which shows that how Brain & Senses process the Shadows ?
Thanks in advance for your helping input.
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Illusions caused by shadows might be one of interesting topics related to shadows. The following article gives some examples of such illusions:
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Hi Friends.
i want to set up an experiment that can adjust the power of light for example 450W/m2, 600W/m2, 750W/m2 and 900W/m2. The light will focus to the plate by fresnel lens. My lens size is 1m X 1m. 
Anybody have experience do the lab test for fresnel lens? Can you share something to set up and run the experiment . In my lab just have solar simulator (Halogen lamp), I can't do the experiment using this solar simulator.
So, i need some idea to set up the fresnel lens experiment in lab environment.
Thanks.
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Thanks a Lot Dr..
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As I am interested in reservoir potential of coal and want to work on coalbed methane. Different technologies and software can be used for it, can you guys upload the list. e.g. the mercury porosimetry, helium porosimetry, mercury intrusion/extrusion curves, etc.
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Methane is a gas.  You can find the properties of it with a Google search.
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I am looking for high power intracavity optics (lens and polarizer). 
Wavelength: 755 nm
Pulse energy density: 1.6 J/cm2
Pulse width: 500 ps
Repetition rate: 100 MHz (during pulse build-up for ~ 2 microseconds)
Since the laser system is q-switched, modelocked and cavity dumped, the damage threshold requirement seems to be significantly higher than general stock optics. I have already damaged stock lenses, and some custom-made brewster thin film polarizer before the laser can reach the target energy.
The beam size has been expanded as much as possible inside the cavity with telescope configuration. Only option seem to be to look for a extremely sturdy optical coating.
Does anybody know any custom coating services that specializes in high damage threshold optics or intracavity optics?
(I've heard that hafnium coating is required for high LIDT but do not know about this in detail...)
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Hi Chanju,
Laser Pulse damage is always a difficult topic, as polishing, coating, cleaning and operational temperature play a role.
To my knowledge ATF is a supplier not only for high reflectivity but also for high power coatings:
However we in Germany usually order the coatings from Layertec and LaserOptic:
I hope presenting this variety the keeps me from the accusation of being biased.
However I have a very different question: What is the q-switching repetition-rate and the average power? We as disk laser developer normally use lenses just for the pump light. Intra cavity the only transmittive elements are the active medium, wave plates and Pockels cell. Are you sure, the lens was not affected by the average power of nonlinear absorption? Just an idea,
 I hope I could help.
All the best,
Karsten
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I am interested to measure the intensity of light in individual arms of a Cyclic Shearing Interferometer.I am facing an issue in this regard and that is as I am trying to place my CCD in any of the arms it blocks the passage of light which stops the intereference itself on a plane.And that is making the intensity measurement due to individual arms troublesome.
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Perhaps beam splitter in desired arm will help you.
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1 how to calculate? Is it the ratio of the amplitude of the reflected wave to the incident wave?
2 use which device to measure it? Is it accurate enough?
3  Is there any simple method to measure the wall reflectance? I just want to be sure that the recommended value of 0.5 for simulation is not far from the fact.
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I agree with Tobias. We should distinguish between reflection coefficient and reflection factor or reflectance. The former relates the reflected amplitude of the electric field to that impinging in a surface. The reflection factor or irradiance deals with the irradiance reflected. Both parameters are related.
As most instruments measure reflected irradiance, you should calculate the electric field amplitude. However, please, be advised that you could loose the information about the reflection phase change if needed when measuring irradiance. Polarimetry could help you.
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Hello
we know a nonlinear molecule has 3N degree of freedoms. 3 are translational, 3 are rotational and 3N-6  are vibrational degree of freedoms. but The molecule has another degree of freedoms to storing energy and it is electronic levels.
why we don't consider this degree of freedom?
Thank you 
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Hello, 
First, some comments regarding previous postings in this thread:
  1. The vibrational and rotational energy levels in a molecule are not necessarily stable, even if not interrupted by an external factor such as collisions with other molecules. A molecule in a ro-vibrational state i-p can spontaneously decay to a lower state j-q, and the probability for that is the Einstein A coefficient for that transition.
  2. The translational energy can also change, even if not interrupted by an external factor such as collisions with other molecules, as the molecule can spontaneously dissociate, so we cannot talk of the same molecule any more.
To the question, yes, the electronic levels of a molecule can be regarded as degrees of freedom such as vibration and rotation, and it may make sense to do so, such as in the final stages of an isotope separation process. However, it is more often the case that the ro-vibrational energy range involved (eg, in the infrared for molecules) is very far from the electronic level energy range of the molecule, so as to make both possible and useful to not consider the electronic levels as a degree of freedom.
Further, the translation energy can also be regarded as a degree of freedom in a molecule, as in photodissociation and Doppler effects. For example of the later, the Doppler effect due to the random velocities of molecules in a gas causes a spectral line broadening that prevents a precise measurement of the line center for a molecule at rest. It can also obscure narrow splittings, for example caused by hyperfine effects, that provide information about the molecular wavefunction.
Cheers, Ed Gerck
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I have built time domain models of Ag nano particle and all seems fine when I simulate at SPR maximum wavelength. But when I compare the near field enhancement factor with wavelength domain model, they don't match. Also in the time domain model silver seems to exhibit high near field enhancement values even in the visible region (500-600 nm). Can someone suggest if it is appropriate to compare the results of similar models between time and wavelength domains (theoretically it  should be same)?
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I am not sure the reasons. Do you correctly consider the density of the incident light.  Another possible reason may be the accuracy of the time domain method  which is not enough.
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Dear All,
I need to construct phantoms with defined optical properties and I am using materials/chemical that their optical properties are not available. I need to know their optical properties to find out how much (in terms of amount/concentration) of them need to be mixed to create my desired optical properties within the medium (final form).
Also to make sure about my analyses I am interested to measure optical properties of materials by myself in the lab.
So was wondering what are the methods available to measure these coefficient quick and cheap? I know that there are methods like integrating spheres but I don't have access to such an instrument.
Thank you very much. 
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How to calculate the beam waist of  Gaussian beam from its intensity in a crystal? Is there any direct relationship between the beam waist and intensity of a gaussian beam?  
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you can use a power meter and a knife edge.
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Is it due to fact that light slows down in higher refractive index region. So the material force the light within itself. 
Same like a water is flowing in pipe , it flows smoothly but in the case of oil flowing in pipe, it flows slowly.... But in this case instead of refractive index, we have viscosity.... 
Could you please confirm this please 
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@ Waseem
First have a look at the actual physics and then the analogy.
Physics: Light or in general say EMW comes in small packets (quanta) of energy called photons. As the photon goes through the material, it interacts with the constituent atoms of the material. Depending on the properties of incident radiation and the material, it could give rise to one or many phenomenon such as absorption, attenuation, dispersion, scattering etc.
For the sake of simplicity lets assume the medium is electrically neutral. That is, the dipole moment of all constituent atoms is zero. However, in most medium the incoming radiation field momentarily polarizes the constituent atoms of the material.  As a result the positive charges (protons) and negative charges (electrons) inside the atom are separated by a finite distance giving rise to a non-zero dipole moment of the atom. But, remember this happens at a very short time scale (10^-12 to 10^-18 seconds or so).
Also, note that prior to the disturbance created by the radiation field, the charges (positive and negative) weren't separated by any "appreciable" distance and that's why the dipole moment was zero.
Once the polarization (though at very short time scale due to absorption of the photon) has taken place, each atomic dipole in the material acts as a phased array antenna. But, this polarized state is highly unstable and so the atomic dipole re-emits the absorbed photon with some delay of-course (10^-12 to 10^-18 seconds). After emitting the photon, the atom returns back to its initial de-excited neutral state. The process repeats across the material along the path-length of the photon as it encounters one atom after another along its flight. In essence, the time duration to cover the path inside the material becomes longer compared to the same length traveled in vacuum where there was none to interrupt the photon path. This is why light has different speed in different materials. 
But in reality light's speed  remains the same independent of the material. The speed of light remains the same in going from one atom to another in any material. It is the absorption and re-emission of the photon by the atom which introduces a phase delay in the path of photon. Hence, it is more suitable to refer to "phase speed" of light in any given medium.
Analogy: Think of it as a relay race where runners of a team carrying batons travel with the same speed (speed of light, c). But, when the baton is passed from the hands of one runner to another, some time is elapsed. It introduces a delay! Passing of baton from one runner to another is similar to absorption and re-emission process of photon inside the material. This causes the final person (i.e., the emergent ray) to arrive to the finishing line much later than he would have arrived had there been no delay (case of vacuum).
Hope that clarifies!
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In the context of a Joint spectral amplitude of an SPDC effect is it possible to model a cw-laser with a dirac delta function?
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It is not fully clear from the question which properties of the laser you are interested to model with the delta function. The most obvious candidate would be the spectral power density. As mr. Tikhonov pointed out, the linewidths of proper single-longitudinal-mode CW lasers can be quite narrow, and, depending on the process you're modeling, it is indeed likely that a Dirac function may be a good approximation of the narrow Gaussian or Lorentzian spectral line-shape.
I suppose you would have to compare the linewidth of your laser to other spectral widths in your problem to see if it's much narrower.
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I am working on a project which contains study of storage of different shapes of pulses in three-level lambda system. How can I solve equations involved in adiabatic approximation ?
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Hi!
In case you would be interested in reading about the adiabatic approximation (and the related Berry phase) in the general quantum mechanical setting and taking a look at some relevant general equations, a concise but clear treatment can be found, for example, in L. E. Ballentine, Quantum Mechanics: A Modern Development (World Scientific, Singapore, 1998), Ch. 12.7 (p. 363). It does not discuss solving the equations, though. Good luck with your project!
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it is a CW fiber laser(1080nm) ,i want to design a isolator for it to cut high reflect material
with 500W.
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i can not agree more with  mikhail. laser beam is random polarization for industial.faraday isolator must be polarized and the space combine is difficult,not stable.i think the fiber  coulping may be a good way in theory.
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I am able to convert wavelength(nm) values to photon energy(eV) but I could not find out how to draw Tauc Plot from these values (i.e., reflectance and photon energy)
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Dear colleague Yeswanth Rayapati
Have a nice time and good day.
Herein fined all what you need about optical properties from A to Z. in details including the direct and indirect transition akso the references are included.
Due to the format of the Equations, it is included in the attached file so check the Eq. No. the see it in the attached file.
First you measure transmittance, T reflectance, R and/or absrobance using any spectrometer. 
If your spectrometer is not calibrated so you need to  calibrate your measured parameters otherwise go to step 2. Herein fined how to calculate the optical gap and constants of the film also the references are mentioned and all you need to overcame the all problems of optical properties [five items]. Due to the format of Equations it is attached in a separate file, just you know the equation number please check it through the attach file.
1- How to calculate the correction of T and R?
The reflectance was measured at normal incidence with an aluminum reference mirror. The absolute values of  transmittance, T and reflectance R of the substrates after correcting the  are given by [[**]A. A. Sagade,  R. Sharma, Sensors and Actuators B: Chemical, 133 (2008) 135-143 [**] M. Dongol, M. M. El-Nahass, A. El-Denglawey, A.F. Elhady, A.A. Abuelwafa. Current Applied. Physics 12 (2012) 1178.]
Equation No.……………………………...... (1)
Ift and Iq are the intensities of the light passing through the film-quartz system and the reference quartz, respectively, and Rq is the reflectance of quartz. In addition, if the intensity of light reflected from the sample mirror reaching the detector is Ifr and that reflected from the reflectance reference mirror is Im, then
Equation No.…………………… (2)
Ifr is the intensity of light reflected from the sample reaching the detector and Rm is the mirror reflectance.
T and R spectra were performed on thin film samples with single face. Extinction coefficient, k and refractive index, n were calculated using T, R and thickness d taking into account the experimental error of   the film thickness. T and R.
2- How to calculate  Absorption and extinction coefficient?
T, R and d are used to calculate the absorption coefficient, α
according to [[**]A. El-Denglawey, M. Dongol, M.M  El-Nahass, J. Lumin 130 (2010) 801.]:
Equation No.………………………….…….…… (3)
α is given by:
Equation No. …………………………………… (4)
The calculated α is included within high absorption region (α ≥ 104 (cm)-1).  
Extinction coefficient, k of TiO2 film is calculated by using:
 
Equation No. ……………………………………….…. (5)
3- How to calculate  Optical gap?
            An absorption edge of semiconductors corresponds to the threshold of charge transition between the highest nearly filled band and the lowest nearly empty band. According to inter-band absorption theory, the film’s optical gap can be calculated according to [[**]J. Tauc (Ed.). Amorphous and Liquid Semiconductors, Plenum, New York, 1976].
 
Equation No.…………………………. (6)
 A is a parameter of transition probability, it measures the disorder of material 
A = 4πσmin / nc∆E, Where  σmin is the minimum metallic conductivity, n is the refractive index, c is the light-velocity, and  ∆E = ∆Ec - ∆Ev   represents the  band tailing
[[**]M. M. El-Nahass, M. H. Ali, A. El-Denglawey Trans. Nonferrous Met. Soc.     China 22(2012) 3003−3011].  
is the optical gap of the material, hυ is the incident photon energy and r is the transition coefficient. The reported values of r are 2 for the measurement of indirect optical gap and 1/2 for direct optical band gap.
4- To determine the value of r plot the relation.
In case you know the value of Eg from the literature you can use:  ln (αhυ) = ln B+ r ln(hυ- Egopt) and find the value of r from the slope of the line for Ex.
 May you have both direct  and indirect band gap
The indirect optical gap, is evaluated by extrapolating the straight line part of (αhν)1/2 curves with energy axes (hυ) i.e (αhυ)1/2 = 0  according to eq:
Equation No.……………………………. (7)
Direct optical gap,  is evaluated by extrapolating the straight line part of (αhν)2 curves with energy axes (hυ) i.e (αhυ)2 = 0  according to eq:
Equation No.……………………………. (8)
Both direct, and indirect, optical gaps of TiO2 films may be found.
OR
to find the value of r the relation between (αhν)^1/r and incident energy (hν) for all values of r should be figured. The value of r which release a straight line represent the value of r and the electronic transition type.
5- How to calculate refractive index and dielectric constant?
Both R, and k at different λ were used to calculate refractive index, n according to:
[[**] T. S. Moss. Optical Process in semiconductor. Butter Worths, London, 1959.]
Equation No.     ………………………….… (9)
The dispersion of refractive index of the films is analyzed by the concept of the single oscillator and can be expressed by the Wemple–DiDomenico (WDD) relationship[ [**][S. H. Wemple, M. DiDomenico. Phys. Rev. B 3 (1971) 1338-1351] as: 
Equation No.          ……………….(10)
 Eo is the single-oscillator energy and Ed is the dispersion energy which is a measure of the intensity of the inter-band optical transition, it does not depend significantly on the band gap. The oscillator parameters can be determined  by fitting a straight line to the experimental points according to [[**][A. El-Denglawey. J. Non-Cryst. Solids 357 (2011) 1757-1763].
Plotting  vs (hν)2 allows to determine the oscillator parameters by fitting a straight line to the experimental points. By extrapolating the linear part of WDD optical dispersion relationship towards the infrared spectral region (hν = 0), static refractive index n(0), could be defined by the infinite wavelength dielectric constant ε∞ or n(0)2,
The relation between the lattice dielectric constant εL, and the refractive index, n as
[[**] A. El-Denglawey. J. Non-Cryst. Solids 357 (2011) 1757-1763.]:
Equation No. ………………………………….(11)
where εL is the lattice dielectric constant, N/m* is the ratio of the carrier concentration to the effective mass, c is the speed of light, and e is the electronic charge, εo is the permittivity of free space. The linearity of the plots of n2 versus λ2, verifying of Eq. (11). The value of εL is determined from the extrapolation of these plots to λ2 = 0 and N/m* from the slope of the graph.
Please notice that there is a direct calculation of ( hu) by this relation using wave length only.
E= hu =1240/wavelength (nm). 
I wish that is useful and help you.
Don't hesitate to ask about any thing concerning optical, electrical and structural properties.
Good luck
Yours
A. El-Denglawey
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I use mie theory for predict light transmission of optical ceramic but when I depict the curve transmittance increases in all  lambda while must be decreased in several lambda. I d not know what is wrong in my calculation. please guide me.
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then either your formulation or your code is wrong.
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I need an collimated light source in my optical system, and the size needs to be very small. I searched the SMD LED, but to find that the emitted angle is quite large (usually 140 or more). Could anyone give me some advice? 
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hi ke
how much power are you expecting out of the lens?
we, at prizmatix, have a small collimator for a variety of LEDs
for instance:
this has a beam diameter of 22mm, which might be too big for you, but we also have this system, with a 0.5" collimator:
which might be good for what you need
arie
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I want to use the Channeltron to detect the very weak VUV photons @150-180 nm.
The Channeltron is applied by 1500-2500 V high dc voltage, and connected to a photoncounter. When change the discriminator level of the photoncouner, the dark counts are schmatically shown in the attahced figure. My question is where sould I set the discriminitor level when detecting the VUV, setpoint at A, B or C?
Thank you in advance.
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If my understanding is right, then you should put the level at C: right after the sharp fall of the count plot.
Consider what happens when you steadily decrease the discrimination level from point above C. At such high levels the current spikes due to the dark counts do not pass through the discriminator. Hence, the count is low. As you pass below point C the discriminator level is roughly equal to the level of pulses due to the dark counts. Hence, the abrupt increase of the count. However, if the discriminator level is further decreased then so many dark counts pass through the discriminator that pulses began to overlap in time; therefore, discriminator counts many such overlapped spikes as a single one. Recall that before discriminator can detect one pulse the previous pulse should decay below the discrimination level. This leads to the decrease of the count, but this is just because the oversaturation of the detection system (point B shows the saturation).
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I'm curious about the configuration of the reflected circularly polarised light for a half-wave plate on a mirror.
A half wave plate will flip the handedness of CP light (left -> right, or right -> left). Similarly, upon reflection from a mirror, CP handedness will also flip. So, if we imagine R incidence, if a half wave plate is atop a mirror, will the CP light be flipped at the bottom of the HWP (becomes L), then flipped by mirror (becomes R again), then passes back through the HWP to be flipped again (so finally leaves as L). So R -> L or L-> R for a HWP/mirror configuration?
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Hi Mitchell --
That's a fun yet instructive optics problem, especially if you were to tack on minor tweaks to make other interesting scenarios -- some examples could include using a quarter-wave plate. launching elliptical polarization (like Ex=Ey&&phi!=pi/2 or Ex!=Ey&&phi=pi/2), tuning the axes of the wave plate to be at different angles than the semi-major and minor axes of the polarization ellipse (for elliptically-polarized light). or using a non-normal incidence angle where the phase shift is no longer the same for both polarization components.
There isn't much to add to what has already been said in confirming your line of thinking, so I'll just add one extra bit that only matters for situations involving very short pulses: when using waveplates with pulses containing only a few laser cycles, it's important to remember that a full-wave retardation (like in your scenario above) still constitutes a one-cycle delay (or multi-cycle integer delay, if using a multi-order half-wave plate) between the o-wave and the e-wave. If the pulse is, for example, only two cycles long, then the emerging o- and e-waves are no longer well-overlapped in time after being delayed by one cycle, so the effect is no longer null (as in the case with long-pulse/cw light, where a delay of a full 2pi is essentially negligible) and the polarization is time-varying.
Thanks for the good idea, ~Eric
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When I calculate the second-order nonlinear optical susceptibilities by using Method from S. Sharma(DOI: 10.1103/PhysRevB.67.165332), I get d33's shape like the image attached which the absolute value of d33 decrease with increased incident light energy under the resonant frequency.  In my experience, I always get second-order susceptibilities shape like images of d11.png and d15.png attached.
My questions are:
1. Is the d33 behavior an abnormal one or normal one or wrong?
2. What is the physical meaning of negative second-order optical susceptibilities? Could you give me a clear and easy physical model of explanation?
Thanks.
Jason Yu from Chinese Academic of Science.
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Why don't you email Prof. Draxl with the question or at least ask her how to contact Sharma.  Google Ambrosch-Draxl and you will find links to her research group.
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Good morning, I am a graduate student, new in researching the transmission and stability of optical solitons. I've read some articles about it, and a method named 'Vakhitov–Kolokolov criterion' have been metioned many times. I am curious about it, also confused.
Could anyone tell me about Vakhitov–Kolokolov criterion in briefly, or introduce some articals deducing it detailedly to me? 
I will be  deeply grateful.
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Dear Prof. Gert Van der Zwan
You are right.
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Optically, this gap is measured by observation of electron transitions HOMO-LUMO, that is to say the transition absorption of lower energy or the transition to higher-energy emission?
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when energy state electron was externally  add some energy, electron will have jump lower stated to higher state.
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How to select the SESAM's parameters like modulation depth, saturation fluence, and recovery time according to my laser cavity with wanted pulse width and output power?Is there any formula to calculate those parameters?
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Dear Chao,  SESAMs were  developed into intracavity saturable absorber devices because of  inherent simplicity with this structure.  The use of SESAMs has enabled CW mode-locking operation  with the pulse durations, average powers, pulse energies and repetition rates of ultrafast solid-state lasers to be improved by several orders of magnitude compare to just nonresonant Kerr-type phase nonlinearity. You know SESAMs have over other saturable absorber techniques because its absorber parameters can be easily controlled over a wide range of values. But single relation describing pulse parameters under  SESAM mode-locking with all nonlinear absorber parameters doesn't exist. You can try to achieve best parameters of pulse lasing  for your  laser with SECAM.. and this way will be successful because You know wavelength  and lasing power and cavity length for your laser. So order or  make SESAM  with resonant absorption for your lasing wavelength and relaxation lifetime  at least less than cavity round trip-time  (2L/c) because it affect on modulation deep at given intracavity  lasing  intensity. (for this case there is known expression for saturation absorption).
So warmly greeting You
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Is there any open library of designs for making diagrams of optical setups?
For instance, I've found this:
But it's focused more to gravitational waves type of experiments; for microscopy, it doesn't even have an objective...
Just wondering before embarking into expanding it ;)
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Stefan,
didn't know pst-optexp, it looks neat, but I guess it takes a really long time to be proficient at it ;)
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I have an argon ion laser (cw) with wavelengths from 457-647 nm. Initially they are all together but I am interested in picking up the 488 nm line and mantein its spot size. I have seen there are many kind of prisms and as I am pretty new in this area I would like if anyone could give me any advice.
Many thanks for your help.
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You don't need a pair, a single prism is sufficient. The linewidth of the 488 nm is so small that the beam won't diverge (i.e. have any appreciable angular dispersion) after the prism. Look around in your lab, the first prism you find that is transparent, will work. Otherwise, use the cheapest BK7 prism from Thorlabs.
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Explain in your words. 
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adding a layer onto a particle refractive index will be shifted towards that of the layer.
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there is an ambiguity between depth resolution and depth of field, and the two both depend on recievers and displays. 
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The depth resolution of the (imaging) device corresponds to the smallest axial (depth) distance between two point objects that the device can resolve. The depth of field is an axial (depth) range where the object stays in focus.
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I want to transmit a dual tone or dual wavelength optical signal (i.e. the multiplexed one) through a standard single mode fiber, but when I transmit the signal it gets distorted because of various reasons such as dispersion, phase noise etc. so it would be very much helpful if anyone share experience working in this field. Thanking you,
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Dhiman,
I still don't fully understand the spectrum of the signal you are trying to propagate, and how it is modified along the link.
If you amplitude modulate the signal at 50 GHz and 60 GHz, then you will probably get tones at 193.04, 193.05, 193.10, 193.15, 193.16 THz - a spectral width of 120 GHz - with more tones possible depending on the modulation scheme. How is the modulation applied?  Do you apply CW modulation and adjust the amplitude to suppress the 193.1 THz carrier, or is this always present?  Do the +/-50 GHz tones propagate over part of the route with additional tones added when the uplink modulation is applied?
Do the 50 GHz and 60 GHz microwave signals carry DQPSK data, or do you extract CW tones and use a pair of Mach-Zehnder modulators to apply the modulation to a single spectral line? 
What is the symbol rate for the data modulation?
As I said previously, if you are trying to propagate a 60 GHz microwave sub-carrier, it will be heavily distorted within a few km. 
If you modulate an optical carrier directly with DQPSK at 10 GBd or less, you should be able to propagate over 60 km SMF with tolerable distortion, provided you optically filter unwanted spectral components at the receiver.
Regards,
Alan.
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That is in RE, like Ce, Er 3+
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I think that Roman's explanation is correct and maybe perfect. However, I would like to add a rule of thumb.   "Forbidden transition is narrower than corresponding allowed transition."  
While 4f-4f transitions are forbidden ones, the 4f-5d transitions are allowed. (f-f: the same parity, i.e., forbidden. f-d: different parity, allowed.)
I don't know why forbidden transitions are narrower.
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