Optics and Lasers - Science topic

Dear Tatiana Loukina ,

unfortunately you are not author/co-author of that publication, so you have no access to the RG publication

and you cannot edit the author details via the instructions given in the following support page:

https://help.researchgate.net/hc/en-us/articles/14293081125777-Reviewing-editing-and-featuring-your-research.

The only thing you can do is to contact the RG administration (e.g. via the 'contact page') and report that issue

See the very upper right entry "contact us" at the

ResearchGate Help Center Page

Best regatds

G.M.

Yes, it is possible to measure spatial coherence using a Cyclic Shearing Interferometer (CSI). Spatial coherence refers to the correlation between the phases of a wave at different points in space. The CSI is particularly well-suited for this task because it can measure differences in phase between slightly displaced points in the wavefront.

In a CSI, a beam of light is split into two paths, and one of the beams is sheared or displaced with respect to the other. The two beams are then recombined, and the resulting interference pattern is observed. The visibility of this interference pattern (i.e., the contrast between the bright and dark fringes) is directly related to the spatial coherence of the light.

By analyzing the fringe visibility as a function of the shear distance, one can determine the spatial coherence length, which provides information about how coherent the light is over a certain distance. The method is effective for characterizing partially coherent light sources, such as lasers with finite beam quality or extended sources.

For other fields (Nursing World, Health, Biotech Congress, Cancer Science, Pharmaceutics, Entrepreneurship Summit, Women's Forum, Petroleum Summit, Earth Science Congress ...) you can check them on this website:

It is also on ResearchGate. Author Shangli Pu. Measurement of refractive index of magnetic fluid by Retro - reflection on fiber optics end face.

Dear Joshua,

Let me try to help you.

# In order to eliminate or reduce the cosine error, in my opinion, you should have to tilt your laser head so that the misalignment angle (theta) is sufficiently small. You can do that by trial and error.

# In order to eliminate or reduce the abbe error, in my opinion, you should have to reduce or remove abbe offset (d). In my understanding, there are any 2 (two) methods, i.e. Zero abbe offset configuration and Abbe error compensation. Please see on the attachment file. The disadvantage of Zero Abbe offset configuration is the system size becomes large. For Abbe error compensation, I did not have experience with it. I am still learning about Abbe error compensation. Generally, you need a double pass interferometer. I suggest you read the publication from Dr. @Jong-Ahn Kim. I remember that he published a paper in 2012 about angular compensation to remove abbe error. He is an expert in this field.

what is the effect of the increases of the number of rings

Abbas N. regarding your 3 points:

1) There is no need for the lens NA to equal that of the fibre. Usually, coupling will be more efficient if the lens NA exceeds that of the fibre, provided the lens aperture (entrance pupil) is sufficiently large to avoid vignetting the input beam.

2) Coupling is optimised when the beam is focussed to a spot whose field profile matches the field distribution of the fibre mode. Typically, both launch spot and mode profile are approximately Gaussian, and the matching criterion is for the launch spot diameter to equal the mode field diameter.

3) Launching the collimated input beam parallel to the optical axis of the lens which in turn is coincident with the optical axis of the fibre will minimise mode mismatch due to tilt errors and lens aberrations.

More specifically, you specify a beam quality factor M² = 1, so the beam is close to an ideal Gaussian beam. When focussed by a lens, the radius of the beam waist at 1/e² intensity, w₀, is related to the wavelength, λ, and the divergence half-angle, θ, also at 1/e² intensity by: θ = M² λ / π w₀

Your collimated input beam width is W=0.65 mm. If the focal length of the lens is f, the radius of the beam at the lens principal plane is W = θ f = f λ / π w₀

provided the lens NA > sin θ. https://www.newport.com/n/gaussian-beam-optics

The fibre mode field diameter will be comparable to the fibre core diameter, but need not be identical. The relationship depends on wavelength, and the extent to which the evanescent field extends into the cladding.

If we assume that the beam spot radius is equal to the fibre radius, w₀ = a = 1 μm, then we require a lens focal length f = π W w₀ / λ = 1.98 mm.

A larger mode field diameter will require a proportionately larger focal length. A 2.8 μm mode field diameter will require a focal length of approximately 2.8 mm. The exact value is not too critical. If the mode field radius is r₀, the coupling efficiency (assuming Gaussian profile for both fibre mode and excitation) is:

η = 4 w_0² r_0² / (w_0² + r_0²)²

A 40% mismatch between launch spot diameter and mode field diameter degrades the theoretical coupling efficiency by only 11% (to 89%).

Regarding the choice between microscope objective and aspheric lens, both are capable of diffraction-limited performance for a monochromatic beam aligned with the optical axis. The microscope objective will be more complex, because it must deliver high resolution imaging over a relatively wide field of view, with illumination comprising a broad range of wavelengths.

The exact focal length of microscope objectives is not always stated. Magnification depends on the distance between objective and eyepiece. Tube lengths of order 160 mm are common, so a crude estimate for high power objectives is focal length f = 160 mm / magnification.

The 60x objective suggested by Suchita Yadav. would have a focal length around 2.7 mm, and would be a reasonable choice, especially if the fibre MFD is larger than 2 μm, but an 80x objective may be better. A 40x objective with 4 mm focal length is probably be too long.

If the microscope objective is optimised for visible wavelengths, there may be some additional losses due to surface reflections at infra-red wavelengths.

Note that a weak supplementary lens can be used to modify the diameter of the beam as it enters the focussing lens, and adjust the spot size for optimum coupling.

Hope this helps.

I am Dr. shoaib from Pakistan working on glass and single crystal materials. our group is working on preparation and characterizations, e.g. physical, optical, luminescence, radiation, shielding and defect study.

please let me know how we can work together?

email: mshoaib694@gmail.com

our lab head: Gul Rooh (gulrooh@gmail.com)

You need to find an expression for your elliptical beam. I am assuming it is a simple product of a Gaussian beam in the x-direction and the y-direction. You want to have this normalized so that you know that the total integral of your beam profile is equal to 1. Once you have this normalized you know that the power distribution is the total power times this normalized distribution.

In brief, I think you want the normalization constant. In your case this appears to be \pi*w_x*w_y

Note: there is a factor 2 in your equation compared to mine. Will you be careful with the definition of 'beam radius'? Is this at half intensity? 1/e intensity? 1/e for the field? etc? etc?

In light of above discussions, It is clear that only two methods are possible for getting concentration of unknown samples, First is based on calibration curve and other on is calibration free technique. For getting a good calibration curve with minimum error, one should plot a calibration curve of required element in the similar matrix samples in similar experimental condition.

Dear Sourav,

Thank you for your answer. Could you please explain more about S2 measurement technique ?

Thanks,

@Raju: It may happen that we use such conversion for understanding but possibly no such experimental evidences are available in many cases. Even if conversion is there, it may be well below detection limit and negligible. See sizes of different states, they may find difficult to adjust in lattice etc.In CaSO4:Dy we assume Reduction as per Nambi Model, but experimental evidence is not there. There is no change in colour evan after huge irradiation for CaSO4:Dy, if reduction holds, colour should change. You may contact Dr. B. C. Bhatt, who is also on ResearchGate and has done pioneering work in these fields. I am also sharing the question with him.

You can MathCad, if you have a full formula and coefficients

In addition to the previous comments, bearing in mind the length of the fiber links and the environmental factors, for fine tuning you can use commercially available devices.

See in the link:

Dear Nils-Frederik Hasselmann,

Thank you so much for your answer. I think this paper that you provided helps a lot!

Best,

Yuan

I think Cyclic Olefin Copolymer (COC) is good option

I would recommend buying a collimator matching to your prefered beam diameter:

and a kinematic tilt mount like

maybe also an x/y-shift stage. Precise angle adjustment is much more sensitive and important than sideways shift.

You may get a 5 micrometer beam but at the expense of a large divergence (the beam diameter increases as a function of the propagation distance. To understand this you need to look into the ubject of gaussian beams. It is quite srightforward and very useful if you work with lasers. A perfectly collimated beam really does not exist. Rather than that what you can obtain is a laser that focuses into a waist, at which it is collimated and then it diverges again. The angle at which the beam spreads from the waist is called the divergence angle. The narrower the waist, the larger the divergence angle. Divergence_angle=2*lambda/(Pi*w0). w0 is the beam radius at the waist. This formula is approximate and is valid far from the waist where the divergence is linear with propagation distance.

I recommend you grab any book on optics that has a chapter on gaussian optics to read this subject. It is very interesting.

you have to specify type of the composite (fibers type and matrix type).

Dear sir @ David A. Ackerman , @ Patrick Joseph Bisson , I am very much thankful for your helpful and invaluable comments. 

How long is you fiber? Remember that higher modes and cladding modes may propagate, with loss, along a short length of fiber (up to 2-3m, perhaps more). Are you sure that you're launching a single mode only (spot size and converging radiance angle)?

A long, long time ago, I was tasked with couple an visible argon laser into a multi-mode 50/125 fiber with considerable power. To ensure proper input alignment, I created an microscope/imager with very good rejection for 500nm and shorter wavelengths. This allowed me to inspect the fluorescence produced at the fiber tip to precisely center the spot. If your application lends itself to inspecting irradiance profiles at the fiber tips, it may give more insight. But be very careful regarding eye-safety and keep your laser safety officer involved.

Would something like the cuvette holder sold by Janis work for you? It has a spring that holds down the lid.

"Is it that there occurs some kind of destructive interference between various generated harmonics?"

Yes, that is correct. In a centro-symmetric medium harmonics emitted at different half cycles of the driving laser field interfere destructively in even orders an constructively in the odd orders. However, in a non-centrosymmetric medium the amplitude from different half cycles is not equal and even harmonic emission is observed (see https://doi.org/10.1103/PhysRevLett.109.113901).

Another way to think about it: anything that is periodic in time must also be periodic in frequency. When harmonics are emitted with equal amplitude every T_L/2 (where the laser period is T_L) then the corresponding periodicity in the spectral domain is 2/T_L (i.e. twice the fundamental frequency). 

If your intention is to make the two beams parallel to each other, and they are close enough to put thru a single spherical lens, the best method is to overlap the beams at the focal plane of the lens. The focal plane of a lens is where the angle of a beam entering the lens is totally transformed into position on that plane (Fourier transform of angle to position). Use a lens with a long enough focal length so that spherical aberration is not a factor. Depending on the intensity of the beams you could use first surface reflection off a quality uncoated optical flat (preferably wedged) to reduce the intensity to the point where you can examine the focused spots. Make sure that you observation is at the focal of the lens for the laser wavelength. This will be the position of the smallest spot size only if the beams are well collimated. There is also a slight difference between the focal plane and the position of the smallest spot from a collimated beam, but this should be negligible if you are using a high f# configuration.  Focal length / diameter of 20 will do this, as well as keep you away from spherical aberrations.

Dear Arvydas,

I suggest for you a links and attached files in topics.

-shack-hartmann wavefront sensors: Topics by Science.gov

-lens shack-hartmann wavefront: Topics by Science.gov

www.science.gov/topicpages/.../lens+shack-hartmann+wavefront.h...

-shack hartmann sensor: Topics by WorldWideScience.org

-shack-hartmann wavefront sensor: Topics by WorldWideScience.org

Best regards

Dear Dr Razi

I agree with Dr Raid

Regards

Optics Express 24, 2941-2953 (2016)_Polarization-entangled photon-pair source obtained via type-II non-collinear SPDC process with PPKTP crystal

Hello Johanna  I still have no idea what the level of concentration of particles is in you sample.  Can you post data on this site (if you're using a Malvern) or send to me?  alan.rawle@malvern.com 

How do you measure the background for your sample?  Normally one has the dispersant liquid in the accessory and then adds drops of suspension, paste or emulsion to the accessory until the appropriate optical concentration for measurement is reached.  If you're trying to measure the background first in DI water, then emptying, then adding your sample then you'll have a major problem in at least 3 cases - dissolved salt(s) altering the RI and thus the alignment of the system, possible thermal effects if the temperatures are different and thermal equilibration isn't achieved, the inability to remove dissolved air (easy if DI water is the background as sonication can be used here.

Thank you so much Jayita Patwari,

Yes, You are totally right. I should set up the detector at 90 degree from the excitation.

 I was aslo suggested to re set up the SPCM  by using the oscilloscope.

I would like to let you all know the result here after I finished.

Thank you so much.

Excellent, thank you very much

I know that glavos do well, but are not as compact as I would Need

AO deflectors, I have only used them as attenuators (AOM) or pulse pickers, but never as true steering System.

I am a bit concerned of the Degradation of optical Quality.

I was originally thinking of compact Risley prisms Scanners, but cannot find any manufacturer for those.

Often in these cases you are forced to use a dye that can absorb at your excitation wavelength and emits around your spectral region of interest. Use a quencher like KI to make the dye have a very short lifetime so its emission is like an IRF.

Check out this link: http://www.tcspc.com/doku.php/howto:how_to_measure_the_instrument_response_function_irf

Also see the attached paper for the general procedure

I would suggest maybe the laser dyes Styryl 20 (LC 9940) or Styryl 14 (LC 9450). They are able to absorb around ~530 nm and emit around 930-980 nm. You can check out their specs here:

These dyes may be inappropriate if they are not emitting the IRF in the same spectral region you are planning to do measurements though.

Edit: Those dyes I suggested may not be so good. I re-read your comment and see you are looking at the 1200-1300nm region.

Thank you Shivaraj R Maidur.

Rana,  This site may give answer to your question.  Currently, they plot in visible wavelength region but not in deep UV region.

Regards, Shigeo.

The topology or surface structure of a metal could be modified through either laser ablation or laser deposition.

This will change properties such as wetting, which would have an impact on adhesion.

Reading into both of these methods might be useful, and I imagine there has been other work in this field as laser based processes are not new in manufacturing, in fact a quick google search came up with the following paper on exactly that topic:

In one of the experimentation I observed that the linewidth as well the FSR both are higher than that of required for a comb. So still the question persists whether we can overcome this..

REFRACTIVE NEAR FIELD METHOD CAN HELP TO DETERMINE.

There are many cases where you would not want to use a microscope objective for spatial filtering a laser beam, actually. Microscope objectives can damage from high energy pulsed lasers, and their input apertures are small. For high energy pulsed lasers, I have used a plano-convex lens with a long focal length (1 meter) to prevent air breakdown at focus, and a diamond pinhole instead of a typical pinhole, because the laser would burn through the standard pinholes meant for a HeNe. It just depends on what kind of laser you are using, and the intensity/fluence.

A lot depends on whether your traps are mobile (that is, if they too diffuse) or are fixed, but placed at random. In the former case, decay is eventually exponential in the number of distinct sites visited, S(t). S(t) itself depends on the dimension

S(t)=sqrt(t)     d=1

S(t)=t/ln(t)       d=2

S(t)= const. t for all higher dimensions.

If, on the other hand, the traps are immobile, then you have a stretched exponential

exp[-t^(d/(d+2))]

where d is the dimension. This arises from the fact that you might start in a region where there are exceptionally few traps, and survival is dominated by these events.

However, even in the simplest case of a point particle diffusing on a discrete lattice, there are no analytic expressions to my knowledge.

The literature is rather huge: the following somewhat random choice may get you started:

Havlin, S., Weiss, G. H., Kiefer, J. E., & Dishon, M. (1984). Exact enumeration of random walks with traps. Journal of Physics A: Mathematical and General, 17(6), L347.

Grassberger, P., & Procaccia, I. (1982). The long time properties of diffusion in a medium with static traps. The Journal of Chemical Physics, 77(12), 6281-6284.

You may check if you can use a diverging lens in front of the laser output. That is a lens with convex-concave surfaces. The concave side should face the laser output. 

If you are interested in 4-wave mixing processes transforming post- to prepulses via B-Integral you might take a look at Didenko et al. 'Contrast degradation in a chirped-pulse amplifier due to generation of prepulses by postpulses,' Optics Express, 2008.

Hi Elena,

            https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=2386

Good luck and have lot of patience.

In Conventional Single Mode Fibers, due to change of refractive index along the fiber in x-y direction, where the two state of polarized light propagate, the two polarized modes experience different phase velocity. If the z is the propagation direction, say, at z=L, the two polarized modes, under polarization mode dispersion (PMD), would lag each other, resulting in spread in time of the propagating pulse with a particular input polarization. 

To avoid this effect, polarization-maintaining fiber (PMF) could be a remedy, of course for a short distance applications, such as sensors.  Polarizing optical fibers, such as D-shape fiber also can be used to maintain polarized pulses. 

Dear Cassio Alvarenga your, at first sight, net technical issue raises the main deep questions of the nature (or God).

We will give some, most known examples on this, the subject touched by you, from various areas.

1. All devil sits in trifles.

2. Fly in the ointment.

3. Small additional additives very strongly change taste of tea. The ingenious English physicist Michael Faraday paid attention to it and invented alloyed and stainless steels by entering of small additives in iron of other metals, for example, of molybdenum.

4. The washing capability of anion detergents raises in case of small additives cationic surfactant that contradicts logic. As mixed among themselves in an identical proportion cationic and anion surfactant is compensated each other and this mix doesn't wash at all, etc.

5. Thus, it is possible to draw a conclusion that efficiency of the active environment depends on a right choice of the main gases of the gas laser and additional small additives. It is a lot of work, to touch and mix together different gases in big and small proportions.

Sincerely,

Alexander, PHD "Laser Physics", 1992.

Dear Naim,

If you are using standard V-grooves, for coupling, you may try graded index (GRIN) optics. As you know, graded-in and graded-out structure of this type optics will help you to collect the light and then focus it on PD more efficiently.

Good Luck

Farmarz

Dear Alan,

Many thanks for these comrihensive information. Please, allow me to continue the discussion via e-mail.

Best regards

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

Dear Benjamin,

Certainly, near field exists at the tip of an untapered fiber, as well. Please refer to Petermann Formula (Type II).

Assuming your instrument is calibrated properly: If the instrument also detects scattered light from the sample (depends on the geometry), then you should also think of fluorescence as the reason behind increased signals.

Also, take into account that laser ablation in hexane may cause reaction products in the liquid, with a different spectroscopic characteristic than before laser ablation.

Dear Justin,   Integrating the Gaussian intensity function over full beam area (implying infinity) reveals finite integral of the same Gaussian intensity function up to the radius of its beam waist w fills less than 50% of the volume of cylinder I0 pi w^2.   Please see attached my calculation.   Regards, Shigeo.

But, I think, the classification of laser is not your job. If you buy a laser, the manufacture have to classify the laser! Because it depends on some parameters: beam diameter, repetition rate, peak intensity, avg. power, pulse duration, etc.

And second, if you have a laser in the lab, before you use it, you have to contact with special "laser safety person" at your department, who is a certificated safety person.

Best regards,

Zsuzsanna

you can use a power meter and a knife edge.

Thank you Mr. Daniel and Mr. David for your advice.

As I know, depth is related to focal spot size and  wavelength of incident wave in vacume.

depth=k.w^2(w=spot size)

k=(2*3.14)/(landa/n) (landa:wavelength)(n:refractive index)

There are a couple ways to look at this: one is that the time of a pulse is related to the energy by way of a Fourier transform. A narrow peak in time in represented by a wide band in energy (or equivalently, frequency). Also, you might simply realize that if you isolate a pulse quite tightly in time, the uncertainty principle requires that the energy of that pulse be rather broad. Energy (frequency) and time are complementary.

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.

Dindo, is quite impossible to answer with the little info you have. I would just add that it is important to know your  PRF  for the future and there is an easy way to do that using a photodiode and an oscilloscope. I am not sure what is your goal. People log the number of shots for maintenance purpose ( for example, in order to know when to change the flashlamps or filters). However, many components that require frequent maintenance can also be inspected visually in case you don't know the no. of shots/lifetime. For example, If the lamp is old you will see a degradation of the cathode (a bunch of powder accumulated on the inside of the glass) and it needs to be changed. I recommend starting to log all of this info in a laser notebook from now on (daily power output, no. of shots/duration of use, last day when you changed components etc). Normally, each laser should have a notebook associated with it!

you can try using a mixing multimode fiber, and align all the lasers through that.

it will decrease the brightness a little bit.

I suspect that the answer to both is probably at the National Ignition Facility or somewhere similar. They use a two-stage amplifier to generate 351 nm from 1053 nm, with energies in the 100s to kJ to ~1 MJ per pulse. Pulse duration is 10 ns, so of order 10^13-14 W peak power in the 527 nm beam.

Polycarbonate has an exceptionally low intrinsic absorption compared to the AR coating materials. This will probably be no issue. The AR coating will be the first to fail. Assuming the optics will be clean (no dust) and have a surface roughness as expected for the laser optics, the damage threshold will depend on the absorption of the AR coating. You should specify to the coating supplier that only materials with low absorption at 806nm should be used. In most cases, the supplier will do that even without special request, since 808 is a standard for pumping Nd: solid state lasers, with pretty high power in many cases, although most of such optics is made of a fused silica glass. It is impossible to provide a "generic" damage threshold number, but just for order of magnitude, for a "high power laser quality" coating on fused silica  I would suggest an estimation of 1 to 10 kW/cm^2 CW. I am not sure if those numbers will hold for plastic.

It is possible to see into a semiconductor laser if you are willing to use a camera that is sensitive to the laser wavelength.  In this case, a metal contact on the substrate side with a gap parallel to the laser cavity would afford a clear view of the cavity.  The semiconductor material is transparent to the laser wavelength because it must be of higher index to produce transverse confinement.  Looking through the gap in the metal contact gives a very interesting view -- but the light seen is limited to spontaneous emission and a small fraction of scattered stimulated emission.  Nevertheless, you can see the effects of cavity dynamics should a higher order mode take over at some operating current.  Perhaps this is not what you were hoping for -- but such a simple system might be easier to produce than a one-off gas laser with a transparent enclosure.  'All you need' is access to a fab line that makes semiconductor lasers, say at a university, and and a friend who can run a wafer with windows.

I I have little idea oflaser power

Thank you Silver Sauceda, 

Thank you S. Selvendran 

thank you for your responses

Dear Noel! Similar evaluation provides just approximate description. Practically lasing bandwidth depends  from other parameters: cavity, nature of gain band broadening, lasing operation regime (standing or running way, transient or steady state, spatial broadening of gain and mode interaction). The most  bright example  is when laser cavity has so short length  that never mind what is type laser media we have one mode  oscillation. If cavity length is increased to allow two longitudinal modes we will observe them if both fits approximately to half width of gain band. At last  when  intermode gap is small to compare  with gain width lasing is getting many-mode type. All the same total lasing width never be equal to half of gain width due to gain saturation: it stay lesser.

You are welcome

Optical and Quantum Electronics

Wireless Personal Communication

Optik

Well, you want W/m². but you seem to have only a number of photons.

Obviously you need two things:

- the surface of the spot, to obtain an intensity in xxx/m²

- to convert photon into W, you need to know the amount of photon which arrive per unit of time. Then each one of your photon has an energy, in eV, or in J. With the time normalization, J becomes W.

Is that clear ?

Dear Arpit,

It is likely to have coupling between two directions, due to non-linear effects in the SOA. But most of them have same effects on both directions. 

If you want to suppress one, then you need to build up an effect which is only strongly effective for one direction.

Do you really believe what you can see by eye on a paper about focusing a 4mJ pulse in a 10 micron spot? This can be very misleading because neither the response of the paper nor your eye is linear. You may think the part outside the main peak is very intense, but it's probably not. Try to measure the spot with a linear device like a CCD.

Intensity depends on the refractive index of the medium, look it up in Saleh-Teich Photonics or any similar book. Attached the correct definition (intensity is the modulus of the time-averaged Poynting vector, E_0 the amplitude of the light-electric field) and the equation including the refractive index.

Cheers,

Martin

He need pulse energy ~ 1 mJ. You can not get this level with cheap fiber laser.

The D86 is also called encircled energy (but is in fact encircled intensity that is measured and energy is computed), this is generally the way that all short-pulse laser systems measure the intensity on target. This is the technique used in my post above to calculated the spot size from a CCD as you need some point of reference to know where to stop your contour, and this number can be essentially arbitrary because the spot may deviate significantly from Gaussian. Also, this number can be manipulated to make your laser look better than it is, i.e. taking the 50% contour instead of the 86% contour can yield a much higher average intensity, thus as a best practice one should not quote a number, but rather show the encircled energy curve. See attached Fig 2, encircled energy at best focus, and attached image of the focal spot through focus.

Dear Aamir! If You wont to look nonlinear interaction of light with some  substances ask your friends who has Q-switch Nd³⁺- laser to  make with You following experiments (or one of them):

1) Take a short focusing lens and  direct to it laser beam. Without lens beam pass free and You see nothing. With lens You will see creation of bright white point-like discharge that result due to many photon absorption and air ionization. It is eye observed impressive experiment from nonlinear optics.

2) Second  eye observed experiment  You can do if You take small sized crystal powder of dye- Brilliant green and locate it between 2 glass  plates so to direct on it laser beam. When unseen Nd-laser beam 1064nm illuminate spot on dyes the spot will emit green light 532nm in all directions because small dye  crystals are  oriented randomly and every one generate  second harmonic of  incident light. But You must be quite careful against accidental reflected beam of very intensive light from Nd-laser in your eyes. I send  You my  old work with similar  experiments to find efficient substances  for  second harmonic generation. If You make less intensity of Your laser no one  of described results You will observe.

It would be enough for You at the start. And I wish You any success.

Firstly I fully agree with Prof. Muhammad Aslam Baig that intensity is measured as power per unit area.

Moreover, "... spot size is directly proportional to the laser wavelength and lens focal length but inversely proportional to the diameter of the laser beam  falling on the focusing lens.".  

I want to comment on the bold-faced part of the text. 

If we have a laser beam of Gaussian diameter, say, 0.5mm and wavelength of 632.8nm (He-Ne laser) and want to focus it to the minimum spot size (and hence maximum  focus intensity). Then first we should expand it  to a larger beam diameter (and hence lower the intensity), say, 20mm by a magnification of X40 and then use a suitable focusing lens to achieve the min. spot size (and max. intensity). Now larger diameter of the incoming beam  means lesser intensity , and that the spot size can be minimized by maximizing the beam diameter, hence, therefore the spot size may depend upon the incoming beam diameter.

Further, if incoming beam parameters are fixed like its diameter, wavelength. Also the focal length and diameter of the lens is also fixed. Then we might ask if there is any dependence of spot size upon  upon laser beam intensity? The answer lies in the Kerr effect. If the laser is intense enough to produce Kerr non-linearity at the focus, then the beam can be 'self-focused' and the spot size might be further reduced. In the absence of Kerr non-linearity, the beam optics remains independent of laser intensity. Therefore, the spot size will not depend upon intensity.

Laser Physics by Milloni

If you want to filter high intensity or to reduce the fluctuations in the intensity, you can use suitable optical limiters (reverse saturable absorbers).