Interferometry - Science topic

Awaiting for the analysis results' success 😊

Aynı tutarlılık ve fazda o günün atmosfer koşullarında oluşturmak mümkün. Işık spektrumları sayesinde oluşturulan anlık görüntüler o zamanın atmosfer koşullarında elde edilen şekil veya boyutlardır.

The measurement does not directly refer to either length or width of the fibers; the color image shows height information of an area 0.3mm x 0.25mm. The X profile and Y profile show a cross section of the measured surface, along the X and Y axes of the cross which divides the color image into quadrants.

Because the profiles are along an arbitrary direction, they do not follow the fibers but you can get some sense of fibers parameters where fibers cross these axes. These crossing points create the peaks in the profile, which seem ~0.5-0.7um higher than the background and are several microns in width.

You can get a similar estimate by looking at the color image and comparing the colors of the fibers (green) and the background (blue). For a more accurate assessment you would need to fix at least the 2D surface tilt in the image, as Josef suggested above. This is usually a built-in feature of the instrument's analysis software; I believe this is the output of a Bruker tool - they definitely have this.

A quantitative assessment will likely require some image analysis software.

For the coherence time the laser’s frequency and phase are stable(ish). Interfering two snippets of the laser from different times, they may have different frequency and phase, but for a coherence time the frequency and phase of each is well defined and they will interfere producing a beat frequency. After a coherence time their phases or frequencies will have drifted enough that the beat frequency and phase drift. However, if the coherence time is longer than your detector bandwidth, you have already recorded the beats that happened during that coherence time. The beat frequency and phase will drift through all possible relations presented by the bandwidth of the laser, but it will all be recorded in the time record.

Thanks! All the Best!

Hello!! I think you'll have to pay for that. I also think that the code depends on how many signals you are working with. If there are two or three signals the code is not too difficult, I believe.

Doctor has made a great point.

BLI uses substantially more sample volume (something like 20-40uL in 384well, more like 100-200 in 96well), but like others have said, is *mostly* non-destructive (depending on how robust your sample is to agitation and ambient temperatures). BLI is less sensitive than traditional SPR (not suited to fragment screening and other small molecule apps) but is more amenable to crude samples such as sera/lysates etc since the tips are disposable. It's much faster for high-throughput type apps (especially if you can get your hands on the 96-channel top-of-the-line models), and so potentially much faster. Both systems need some amount of knowledge to be used properly. SPR can do some more complicated and interesting things (e.g. enzyme kinetics if you have at least a 4-surface consecutive flow system) and generally more robust data, but more finicky when it comes to troubleshooting. SPR can also be end-coupled to mass spec in some configurations.

Liposomes is a bit vague - is your protein embedded in the liposomes? or you are looking simply at protein-membrane binding? Either way you could have options with both SPR and BLI but you would need to optimize for your application. My personal recommendation is SPR but it may not be entirely objective ;)

Hope this helps

Dear Umer Khalid all these methods are different, but they have a joint qualification as quasi-optimal methods. The optimal method is the Maximum Likelihood Method (MLM). Only ML can efforts Kramer-Rao Bound of dispersion of estimation parameters (angles of arrival as well)

Hi Swati,

Decorrelation in highly vegetated terrain is to be expected and IMHO I don't think the choice of the software will have a significant impact on the results but rather the processing method and the properties of the input data.

SNAP by Esa is a freely available software capable of interferommetric processing, Gamma is expensive (very) but has all one can ask, there are also others e. g. Erdas Imagine

Hello! Have you got any recommendations since your posting? Could you share your experience with me?

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.

The optical filter has to be matched to the phase-matching bandwidth of your SHG crystal. For Ti:sapphire based combs, one typically uses some off-the-shelf PPLN crystals, e.g., for 532 nm wavelength. You can find matching interference filters from Thorlabs or Edmund Optics. You can also use a simple diffraction grating instead. Details on a suitable setup are here: https://www.nature.com/articles/nphoton.2010.91

"Capella makes a portion of its historical archived imagery available through the Open Data Program".

You should specify the energy range.

At low energy, a beam splitter could be imagined by manipulating the absorption of photons, a grating of standing waves for instance, but the wavelength will be such that proper lasers will be difficult to find and it will not work with protons. As to material gratings, the interaction of ions with matter is usually so large that decoherence or exchange of energy with the surrounding will be important.

Here also, it is important to clarify the energy range. From my experience, it is not impossible to imagine a crystal surface that would diffract a proton but: it should be non-polar (otherwise long-range excitation of optical modes would be too important), it should probably not be mettalic because electron capture would be important, it could be an insulator with a large bandgap to prevent neutralization and with heavy atoms to reduce phonon excitation etc...

T.T, thank you anyways

If your electron density is high enough (which should be the case in fusion plasma) you can use interferometry to determine the plasma density or OES. This is provided that you have a suitable line of sight into or through the plasma.

However, which diagnostics you use will be dependent on what you try to measure.

The general relativity becomes engineering science when it comes to e.g. GPS satellites as their oscillators have to be designed knowing they will be noticeably shifted in their frequency once in the orbit.

Also, with atomic clock on the ground one can detect difference in their frequencies when they at different height (just a few meters is enough).

Dear Johan, it´s my pleasure to contribute with the discussion.

1. How useful do you find Examining Interferometrically an Object at 2 different times under different loading conditions?

--Holographic interferometry is usually utilized to reconstruct the phase map of samples from the interferogram, or hologram. It is very suitable for record time-lapse sample changes under different loading conditions in that it allows nondestructive and non-contact measurement and you can perform various kinds of loads while measuring.

2. How much can you or should you vary the different Load-Conditions, while applying Holographic Interferometry to Structural-Component Testing Aspects, without compromising the Wavelength-Accuracy for the overall Structural Component and/or System?

--It's a complicated question. The thing you should consider is how many changes of the sample can your holographic interferometry system record. This involves two aspects: (1) how much information can the fringe pattern carry, and (2) how much can you record the fringe pattern by the camera. These depend on the holographic system you are using, you can provide some parameters of your holographic system such as the wavelength of the laser, NA of the imaging lens(if it has), and so on, for further discussion. Also, you can find further knowledge in any of the literature referring to digital holography, such as the book mentioned by Prof. Dario Ambrosini.

Regards

Thank you for all the input. The mystery is solved. The original photographers sent me a note this morning. The image was created by a one-of-a-kind special polarizing interferometer, similar in design to Differential Interference contrast (DIC) . This special Macroscope was invented by Maurice Françon at the Pierre and Marie Curie University in Paris. The instrument used a 3 inch diameter aperture utilizing a giant quartz optic.

I am still looking up the relevant articles. Thank you all for the help.

You are absolutely right. Compared to optical remote sensing where 'adjacency' is a high order effect the signal impact of 'neighbors' is much higher here. A perfect coherence estimator would include dipol distribution, local 3D geometry for ray tracing and radiosity estimation and a gaussian shaped weighting window to 'reflect' the mixing and superimposition of the representing physical process. I was often thinking to compile a paper about all this in connection with a multi stage, alternative phase unwrapping.... Hope it helps. If not you can send me an email: rogass@gfz-potsdam.de

Several

The material manufactured by laser sintering has a porosity. May be, the increase of feed improve the continuity of the machined surface and diminish the roughness.

Dear Mohammad Abdolrazzaghi,

Here are some references in the theme with other approaches.

Phase-Sensitive Surface Plasmon Resonance Sensors - NCBI

https://www.ncbi.nlm.nih.gov › articles › PMC5751602

Interferometry Using Generalized Lock-in Amplifier (G-LIA): A ...

https://www.intechopen.com › optical-interferometry

Sensitivity-based optimization for the design of a grating ... - OSA

https://www.osapublishing.org › abstract

Best regards

If the the optical path length's between sample arm and camera is not a problem, then you can try introducing a wedge (optics) in the camera leg and relocate the camera to reflected spot from the wedge. Because of wedge angle the back reflected spot can be separated considerably from the main spot. By adjusting the distance between camera and wedge can also help you in separating the beam considerably. Disadvantage of the scheme could be low intensity of spot, but i believe that can be managed by gain features available in camera or with associated electronics for the camera.

Hi;

Optical Methods of Topography Surface Measurement: Confocal microscopy, Focus variation microscopy, Coherence scanning interferometry and Chromatic confocal microscopy. For more details see the following reference: https://www.nist.gov/sites/default/files/documents/oles/3-Vorburger-Ted-Optical-Methods-of-Surface-Measurement-MSSFAA-10jul12.pdf.

With my best regards

I see, you are talking about the deviation of an aspherical wave, generated with a CGH, from a spherical wave.

There is a technical restriction for the maximum local diffraction angle. For spherical waves this means that there is a limitation for the smallest F-number or likewise for the largest possible NA.

In principle, this maximum local diffraction angle restricts the maximum deviation from a spherical wave. But the diffraction angle can change locally very sudden. For example  we are using 'Multi-zonal' CGHs. Here, the diffraction angle and thus also the radius of curvature of the generated wavefront experience discontinuous jumps at the zone edges. This is readily feasible.

So the only restriction I know is this diffraction angle.How large it can be depends on the manufacturing process of the CGHs.

Best regards, Christof.

Dear Dr. Heidi Perez,

I think you can have useful suggestion relating to your detailed question by the following paper:

Cracks, microcracks and fracture in polymer structures: Formation, detection, autonomic repair

Firas Awajaa, Shengnan Zhang, Manoj Tripathi, Anton Nikiforov, Nicola Pugno

Progress in material science 83 (2016) 536-573

Web link: http://www.ing.unitn.it/~pugno/NP_PDF/297-PMS16-fracturepolymers.pdf

Best regards, Pierluigi Traverso

When one derives the Beer's law, they start by dividing the considered medium to infinitesimal slices, each of which contribute a similar amount to the attenuation via an attenuation coefficient. Seeing that the law considers infinitesimal slices, it would suggest that it is applicable also at very short lengths. However, when we use an attenuation coefficient, we assume that the medium is completely homogeneous.

The infinitesimal slices must have differences in how the particles are distributed, and thus the amount of light each slice attenuates should be slightly different. When we have a large number of these slices there is no problem, since the random variances will average out. But for short distances, this might not be the case and the law may fail.

But this is purely speculation, since this is something that would have to be actually measured.

I have a simple package called Fran which you can use. It is old (Best paper mech end 1986!) but has a good phase unwrapper. However it has a problem with large images. (more than 2,000x2,000 pixels). Alternatively recently I completed a contract for MIT (best ASME paper 2018) using software from LuigiChen called UU. or as it now is MU3. The interferometric images were 4,000x5,000 and it worked great. It solved the problems and unwrapped them without problem.

Please contact if you want further details. Let me know if you want further details

Hi,

I know this is an old question, but I want to add something here that might be useful. The unwraping process depends on the size and the quality (coherence) of the input interferogram. For Sentinel-1 full scene, with a computer running Windows 10 (16GB ram, Core i7) it takes up to 72 hours.

Regards

Please go through this website https://vertex.daac.asf.alaska.edu/# . SAR Sensors data are available in this website.

We typically prepare gel for coupling in syringes which we vacumize and then dose the gel between US-transducer and device wall trough which we intend to measure. - This works generally well.

Dear Dr. Friedemann Heinz,

(1) Please find in your e-mail the paper of Lee W. Schumann e.a. suggested by Luis Miguel Gaspar Venancio above.

(2) Since you didn't provide the community with extra details about your application (as requested by Karsten Schuhmann earlier), I dare share only most general (and pactical) thoughts as relevant to your question:

* - the known FT-advantages may be lowered to some extent in VIS or short NIR (500-800 nm) range you've indicated - so dispersive spectrometers may look not so bad alternative here

** - Silicon CCDs perform well in the range you've indicated - especially the so called "intensified", thinned and back-illuminated ones for low-light applications (cf. e.g. Andor catalogues). Certainly, a Pelltier cooling of the CCD is the must

*** - Since we don't know about the resolution you'd like to have (but the higher is the better almost in all instances), I guess an Echelle-type spectrograph would do the job in your case. The constancy of the resolution throughout the measured wavelength range is a favour in Echelle, and the resolution of 1 cm-1 is easily realisable in this case (cf e.g. PE RamanStation 400 based on the Echelle+Andor's cooled CCD optimised for low-light applications). I don't mean that you need namely Raman spectrometer for your application, but using the PE RS400 for some time i'm highly impressed by its sensitivity, resolution and the provided possibility to analyse low-light photon fluxes for very long (many minutes) CCD exposure times.

Hope these notes would be of some help. Good Luck!

@Kassner

"A perfect conductor or perfect electric conductor (PEC) is an idealized material exhibiting infinite electrical conductivity or, equivalently, zero resistivity (cf. perfect dielectric). "

it is perfectly defined and it reflects back anything. A non ideal or non perfect conductor is influenced by its thickness . 

To answer your questions you need to first make interferograms from SAR acquisitions.

So say you have interferograms from scenes captured before and after an earthquake, and you unwrap the interferogram, you essentially have a map of surface displacement caused by the earthquake (with resolution depending on how coherent pixels on the ground are). Now, that allows you to easily invert for coseismic slip distribution on a fault in 3D. But these are only static offsets. You cannot investigate the rupture process with InSAR.

Now, the more fun parts are while dealing with other quasi-static processes like interseismic and post seismic velocity fields (and possible debris flow/landslides). If you collect enough SAR scenes over a particular frame on the ground, you can create a time series of the surface velocity field. Now you can invert that data for slip rates/locking depth of faults/frictional parameters/strain rates (for afterslip/visco-elastic relaxation studies). 

The links that have been provided by some of the other responses to this thread are excellent, and should give you a more detailed description of the possibilities with SAR interferometry.

Alexandrea, using laser source in deep UV region( <250 nm) would eliminate/isolate the fluorescence from Raman spectrum. Working on DUV region is exactly what I am trying to study. However, I would like to know what type of laser can be more suitable in DUV region for interferometry purposes. For example, hollow cathode laser vs solid state one.

Hi, Prof. Yu, I suggest you do once more phase shifting with a different fringe pitch (by varying the angle of reference beam or other means) to separate the interference components from the front and rear surfaces.  A similar problem in deflectometry has been studied by L. Huang and A. Asundi. See attachment for more details.

 I think with fast image processing techniques this work can be done.

Thank you very much, I will search the book from school library

There are problems using SAR: penetration being the primary one. A C-band SAR like Sentinel-1 can penetrate 10s of metres into dry snow. Hence the scattering phase centre is in fact more likely to be at the ground surface than the snow surface. This excludes interferometry. Passive microwave methods are a reasonable estimate: they use absorption by snow cover as a proxy for snow water equivalent but suffer from low spatial resolution and an insensitivity to deep or dense snow cover. Passive microwave methods are also ill suited to mountainous terrain as the algorithms are developed for boreal forest and tundra biomes. Modelling can provide a good complement: statistical modeling using snow covered area and historical snow depth or snow melt runoff data is a good starting point. Snow covered area can be mapped using optical data (in combination with SAR during snow melt). Sentinel-2 offers a wide swath (250km) at high spatial resolution (10-20m in Visible-NIR).

Chris, I assume you want to track phase changes in the optical path in real time. You can use a tracking beam, as your supervisor suggests but, in my opinion, the tracking beam should trace nearly the same optical path as your signal beam. Then, if you modulate your tracking beam with a sinusoidal phase (e.g., using an acousto-optic modulator) and interferometrically detect it (i.e., by mixing it with a splitted version of itself that did not go through the interferometer) the resulting signal will have the same modulation frequency and a phase shift that is time-varying and proportional to phase changes in the optical path.

Then, you can use this "error signal" to correct the path in real-time, for example using a PID-controlled piezo-electric mount that moves one of the mirrors in your interferometer.

-Paulo. 

Contrast, i.e. the visibility of fringes, which depends on your coherent length. Just make sure that they are about the same 'darkness' as they go. If you are doing off-axis, then is it possible that your last piece of work would be the correction for off-axis? 

Thank you so much Laurence  and hashaam sir for such a grate help..

I hope this time i would be able to get my expected result..

Hello, there are two important factors for Stabilisation: amplification for your Feedback loop and Phase responce (or delay of your Feedback). Your Feedback Loop should act in anti-Phase to the incoming mechanical distortion Signal, otherwise instead of damping you will get amplification. Amplification factor of the Feedback circuit should not exceed Level of mechanical distortions. So therefore you Need to characterize mechanical distortions in your Setup and found Amplitude of the Feedback Signal which fit to These distortions. You will Need also to characterize delay of the your piezo-element and Feedback circuitry in order to understand Phase shifts in your Stabilisation System. Regards.

Hi Awan,

What do you mean by Optimise in the context of 2D-arrays ? 

Best of luck.

topographic phase removal is only performed if you need to look for deformation over time (DInSAR), else, skip that step and follow the procedures in graph builder in SNAP toolbox. Given 12 days minimum interval of sentinel-1a, we have to assume that there's no deformation taking place within that period of time. If the period of your study has indeed undergo deformation, you might need to get the DEM before the deformation took place.

Else, if the time issue is important for your study, maybe you can produce both DEM and deformation, then compare their differences. Anyway, sentinel-1a dem is not easy to produce due to temporal decorrelation unless your test site has high coherency (undisturbed/permanent ground features like mountain etc.). The constellation of sentinel-1b is coming so it will probably greatly enhance the

coherency  (see link)

Slide flatness is very important parameter in automated microscopy but slide manufactures do not give the information. In light microscopy with focal depth up to 100 nm glass flatness can be measured using the microscope stages with known planar characteristics. Usually the parameter is more than 50 arc sec

Hello Dear,

I think you can find your answer there,

cheers

reda

Usually when analysing an interferogram pattern, the result will be tilted due to the presence of carrier frequency.. therefore, subtraction of the reference phase might mean removing the tilt from the result.

for Sentinel-1 TOPSAR the steps are .... RADAR----------->Unwrapping----->Export and then go to linux because SNAPHU works under linux and open your share folder includes (EXPORT UNWRAPPING) open SNAPHU.CONF and copy the script and paste it in the terminal and press Enter.....Then after this process go to Unwrapping----->Import and import the ....image file. for more information please visit

Please, read this paper http://arxiv.org/abs/gr-qc/0501041

Dear Alcides,

you can try this book - " Optical shop testing" by Malacara.

Being far beyond the length of coherence of white light, interference fringes are not observable in your device in white light. However, if you filter this light with a sufficiently narrow band filter (e.g. a monochromator), placed before or after your Fabry-Perot, it doesn't change anything, you will be able to observe the fringes. So, it is not because you can't see fringes that you don't have interferences, each monochromatic wavelength present in your white light will interfere with itself (monochromatic light has an infinite coherence length), but to see the effect of these interferences, all these effects must not be too different from one another, in order not to be blurred in the final result. This blurring can either be due to spectral width (referred to as temporal coherence of the source) or spatial width of the source (referred to as spatial coherence).

Hi Mostafa,

Thank you for taking out the time to answer my question. I think that may be a solution to the question however I can clear the question to a certain degree. What I want to do is transmit the zeroth order through the blazed grating which coincides with the other degree and acts as an interference between reference and test beam. I have already speculated the diameter of the zeroth order transmitting hole in the grating and need the angle so that the beams interfere at the sensor. This is why I need the angle of tilt of the slm... 

Thank you.

Regards,

Pratik

As previously stated, InSAR requires coherence between SAR images.  This is the same problem as another SAR exploitation technique, namely Coherent Change Detection (CCD), which after all is just the coherence map.  Relating coherence to collection requirements can be found in several reports and papers, e.g. search for "Collecting and Processing Data for High Quality CCD Images.

I am not sure I did understand the question. A lock-in amplifier should lock the reference frequency straightforwardly. The ref frequency can either be set internally or provided externally by a modulator that is also modulating the input signal. Phase locking is usually done by changing the phase until the amplified signal is minimum or even zero (that is searching the quadrature phase of the ref with respect to the input) and then adding 90° phase shift. Almost all lock-in amplifiers all have the Auto-phase option.  

Hi Xuan,

Depends on your application --> see following links for more information.

Page 12:

Page 27:

Also check:

Tobias

Dear Sebastian:

I think the scheme (in letter "Operation of an optically coherent frequency

comb outside the metrology lab") wil help you.

In our work, we are using swept frequency interferometry for high accuracy absolute distance measurment. We use a tuneable laser from New Focus which operates in the C band.

You may try http://www.mathworks.com/matlabcentral/newsreader/view_thread/281031

Good luck

Pressure changes the RI of water. For details check the IAPWS formulation. Using two step procedure one can calculate thermodynamic properties of water for defined temperature and pressure, which can be used for calculation of RI. Diluted aqueous solutions should exhibit similar behavior.

thanks Mostafa and Canek

But I want to relate the change in refractive with the collected reflected and transmitted photo diode signal during the plasma formation process. 

I think, this paper could be useful:

Improved sample characterization in terahertz reflection imaging and spectroscopy

Don't know if this is relevant but it worked well for us. https://www.researchgate.net/publication/3409359_Thermal_analysis_of_blood_undergoing_laser_photocoagulation

Digital holography or interferometry enables the access to the complex amplitude (real amplitude and phase) of a wave field. If we recorded two holograms, one for the initial state and another after applying a loadmaster, one can then reconstruct two phase distributions which correspond to the initial and deformed states. Thus, one has all information needed to produce interferometric fringes of the difference or sum of displacements.

Don't worry, this is very far from a complicated optical simulation. It's only a 2 beam interference :)

You can model your laser beam as a monochromatic spherical wave. It has 2 reflections from the 2 surfaces of a glass plate. It makes 2 spherical waves whose centers are shifted by a small d distance.

Let's say your optical axis is x, the position of the 1st center: (x1,0), for the 2nd: (x2,0), where x2=x1+d

The phase of the 1st wave in an observation point (x,y) is (2*pi/lambda)*distance between (x,y) and (x1,0) 

What you need to calculate is something like:

I(x,y) = sin(phase1)+sin(phase2)  in a set of (x,y) points.

If you use realistic values for x1, x2, d, lambda (wavelength of your laser), and (x,y) you should get what you want. :)

interferograms 

SARSCAPE is obviously not free, unfortunately.

If you consider free software, give a try GMTSAR on Ubuntu or Mac. GMTSAR use snaphu for phase unwrapping. Someone might think using LINUX is troublesome, but GMTSAR has very good trick to make it works simplest as possible,

It has a straightforward script dealing with focusing your raw data (level 1.0) to phase unwrapping...

1- For Spatial coherence length one can use double-slit experiment .

You could also do this numerically: let coherent light source is fiber coupled and S is the fiber radius,the separation distance between the fiber and theobject plane (or the plane you would like to measure the spatial coherence)  is R. Then the spatial coherence then = 1.22*lambda*R/S

2- For temporal coherence you are right you can use Michelson or numerically you can use what Vladimir said.

Consider also the use of interference microscope arrangements, if you can afford the budget. If you clarify the question we possibly can help better: seeing the interference is just about focusing onto the CCD.

There is news of the White house announcement at last month's UN Heads of State Climate Summit that the global ~30m data will be available from next year (see NASA/JPL news here:  http://www.jpl.nasa.gov/news/news.php?feature=4305 )

Of course, all depends on the detailed optical layout of your interferometer but to previous comment of Patrick Balzerowski I can recommend to r