Science topic

Interferometry - Science topic

Measurement of distances or movements by means of the phenomena caused by the interference of two rays of light (optical interferometry) or of sound (acoustic interferometry).
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Hi, I receive the results of one of my samples (fibres) using White Light Interferometry. However, I do not understand the interpretation of the results (see image), specifically the image about the distribution. Because I am trying to see if the information about those results is about the width or length of the fibres.
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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.
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I was reading a paper introducing the Delayed Self-Heterodyne Interferometry technique by Okoshi in 1980. It was aimed to measure the linewidth of lasers and the main set-up was something like a Mach-Zehnder interferometer, but one of the arms was delayed by a fiber path much longer than the laser's coherence length, and there was an AOM in the other arm [I don't know if it's important]. The interference of these two beams was claimed to indicate the linewidth of the laser. What I do not understand is that how these uncorrelated beams do interfere?
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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.
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I want to know if the number of fringes and their shape is an important factor for the accuracy of phase definition?
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hello everyone!
I hope you all are staying safe and happy!
As a keen learner in optics experimentations. I was looking forward to find the set of experiments for the interferometry. I believe those are from the Newport organization. I was not able to actually. I would like to know if you guys have user manual pdf of the interferometry experiments to be performed , so that I can start with the experiments.
Thank you
I am looking forward to hearing from you all soon.
Regards
Ketan
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Any recommendations about DINSAR (Differential Interferometry Synthetic Aperture Radar) applied to forests?
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Thanks! All the Best!
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Can someone please provide me a Phase Comparison Direction Finding or Correlative Interferometry MATLAB codes?
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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.
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Which are the main limitations of SPR comparing with BLI, especially in terms of buffer and matrix especially for liposome-protein interactions assays ?
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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
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I have studied different papers related to Direction Finding (DF). However, what is really confusing is the terminologies of methods, techniques and algorithms. For example, we have amplitude, phase and amp-phase comparison methods. Once we look at the techniques there are several such as Doppler, Watson-Watt, Correlative Interferometry, etc. Similarly, there are MUSIC, ESPRIT and MLE algorithms.
Now I have really confused, as some papers compare Watson-Watt with MLE, others compare MUSIC with Correlative Interferometry. So is there any difference between these techniques and algorithms, or all of these are just similar alternative names.
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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)
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I was checking Ag-Ab interaction using biosensor (APS)and then I got a association dissociation curve that increasing at both steps and so I need to explain that if there is available reason.
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My first thought here is a buffer mismatch. Have samples been dialyzed to the same buffer, and is the buffer consistent between wells used for different steps?
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The SAR data shows decorrelation for highly vegetated terrains. Has any of the latest software overcome this shortcoming?
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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
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Hello everyone,
Recently, I started studying SAR Multiple Aperture Interferometry (MAI) in order to produce horizontal displacement estimations. I have read some papers but I cannot find any open source code that can help me understand in depth the MAI technique.
This is a paper that i am interested in and related to my question.
If you have been working on MAI, would you please give me some recommendation?
Thanks in advance,
Kleanthis
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Hello! Have you got any recommendations since your posting? Could you share your experience with me?
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I like to do project in laser measurement system. My objective is to eliminate or reduce the cosine error, abbe error in Laser measurement system. I have Rhenishaw XL80 system.
Please tell the procedure to eliminate that particular error. And help me to complete my project.
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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.
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how to do f-2f interferometry from an octave spanning supercontinnum with frequency spacing 120MHz. Which would be the most suitable optical filter in this range for filtering f and 2f components from supercontinnum, to detect carrier envelope offset frequency of a mode-locked laser.
Thanks in advance!
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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
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Dear all, I'd like to open here a sort of forum for understanding how the geodesists community is moving in view of the X-band SAR satellite constellation. The new constellation will offer new "free, near real-time SAR data" with the "latest information about any spot on the planet within the hour". This will open completely new horizons for InSAR monitoring of ground deformation especially for rapid phenomena such as eruptions and seismic crises. The huge amount of so frequent data acquisitions will open also new needs for rapid and automatic processing. My question are: who knows more? Are you planning a routine use of these data? How?
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Wow, thank you. I'm looking for understanding their high-frequency repeated interferometry for ground deformation monitoring. Will data be open or should they be bought?
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I was trying to detect a massive Landslide using the DInSAR technique on Sentinel 1 SLC data but after running interferometry on different pair of Sentinel 1 images, I am unable to detect any deformation in the interested area.
Maybe I have lost coherence values due to Aspect, slope, vegetation, and soil moisture.
Now I am curious to know how to overcome these challenges, and what suitable technique should I adopt to get my objectives using Sentinel 1 data?
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Dear Syed Ahatsham Haider The best technique to work on the landslides or land deformation with vegetation cover is to employ Small Baseline Subset (SBAS) approach; where SBAS approaches account for signal decorrelations by partitioning the data set into several subsets with short spatial and temporal baseline possible (i.e., excluded large baseline interferograms). Within the subsets, the interferograms are spatially multilooked and unwrapped.
he SBAS analysis can be considered as a linear model inversion problem. For each pixel, based on the equation given below:
φ=Ax+Δw
Now coming to coherence, the area as you mentioned is covered with vegetation so there is high probability of decorrelation (within 30 days or less). To overcome this issues you have to use SAR stacks with minimum temporal baseline (incerease the number of SAR images)
Secondly, if your target area is within mountainous region then you have to account for errors due to topographic phase.
The residual topographic phase consists of the height-to-phase factor, elevation error; normal baseline relative to the n-th image with respect to the reference (master) image; local incidence angle; carrier wavelength; zero-Doppler distance between the target and the n-th orbit acquisition.
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An experiment that I propose contains a beam-splitter for protons. There is plenty of articles in the literature, about atoms interferometry. But, except for electron interferometry, I don't see articles on interferometry with charged particles. Whatever I need is a beam-splitter for protons, or ions - anyway, not neutral atoms. The beam-splitter I need should be imbalanced, i.e. the transmission coefficient be different from the reflection coefficient.
Can somebody help?
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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...
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I have stuck with the interferometry of Sentinel-1 data in the phase of coregistration. The SNAP gives java heap space error several times for two weeks. I am finding any freely available software that has used for Interferometric DEM generation. Please help me. Thanks in advance.
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T.T, thank you anyways
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The question has been raised for clarifying the idea of using electrostatic probes in a high dense low-pressure plasma. Primarily the probes would disturb the plasma potential and hence space charges would accumulate in the probe surface, as a result, the sheath dimension would increase. I need some idea for using other kinds of diagnostics which would be feasible for such plasma (interferometry, spectroscopy or other as such). Please recommend.
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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.
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Are there any researchers out there skilled with interferometry who would be interested in a theoretical experiment to test the validity of a certain unverified metric of general relativity? It would be hoped to evolve into an actual land based experiment, however, I am not an experimentalist so I would have more questions than answers, i.e., I would like to exchange ideas with such a person to crystallize the experiment.
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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).
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As recently concluded in a parallel discussion, see reference below, LIGO is unable to exclude that mirror displacements as observed along their interferometer arms in fact result from much larger mirror displacements of similar profile along the vertical.
This is because mirror suspensions act along the vertical which over a distance of 4 km varies by an angle of about 2 arc min (a nautic mile = 1,852 m by definition corresponds to 1 arc min of angular distance at sea level). So every vertical mirror displacement will exhibit a displacement component about three orders of magnitude smaller along the connecting interferometer tube.
As LIGO is unable to directly measure vertical mirror displacements with adequate sensitivity they cannot distinguish whether horizontal displacements such as assigned to gravitational wave interaction are due to horizontal excitation or to vertical excitation at three orders of magnitude larger amplitudes.
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I think Johan concerne about the identidade must be take into account.
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Why Biolayer interferometry (BLI) is considered as a better instrument than surface plasmon resonance spectroscopy (SPR) in measuring label-free protein-ligand interactions?
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In my impression, the major advantage of BLI is easy-to-use and a little bit higher throughput. As to the sensitivity, we have determined the binding kinetics of 124Da pyrazinoic acid on the pyrazinamide-target protein, PanD.
Sun Q, Li X, Perez LM, Shi W, Zhang Y, Sacchettini JC. The molecular basis of pyrazinamide activity on Mycobacterium tuberculosis PanD. Nat Commun. 2020 Jan;11(1):339 <doi:10.1038/s41467-019-14238-3>
I also made an R package to implement our data analysis routine. It's in the CRAN repository, and free to download and run on your dataset now.
Sun Q, Li X, Sacchettini JC (2020). smoke: Small Molecule Octet/BLI Kinetics Experiment. R package version 2.0.0. https://CRAN.R-project.org/package=smoke
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Since, Holographic Interferometry Focuses on the Formation and Interpretation of Fringe-Patterns, it should be noted that any changes experienced by the Structural-System and/or Object over a Predefined Time-Range can be detected with Wavelength Accuracy. It should further be noted, that it is the Time-Variable, that is of importance in Holographic Interferometry, which makes the Non-Destructive Testing [NDT] applications possible and interesting.
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?
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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
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A student sent me this image and asked how it was done. My background is in optics, but it has been a number of years since I worked with surface interferometry.
I am wondering if you can identify what type of surface interferometry system was used?
Description: with the image
For this image an interferometer was used to measure and photograph the interference patterns made by a group of water striders (family Gerridae) as they walk on the surface of water.
Credit: Perennou Nuridsany/Science Source
What we know so far:
Images and still photographs were done by a French team(Claude Nuridsany and Marie Perennou). They have not answered any emails about this technique.
Taken on film at least 15 years ago, but is probably older.
Color is real (not applied with computer)
The technique is described as interferometry
The insects are on water, the light could be transmitted through the container or reflected from the surface. I suspect it might be light reflected from the surface.
We found a movie at:
This question that has caused quite a debate over the last few weeks.
Thank you for the help.
The image here was found at ScienceSource a science stock image site
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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.
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When calculating interferometric coherence, why can't you do so on a pixel by pixel basis? I know the equation for estimating coherence = (|S1∙S2* |)/√(S1∙S1*∙S2∙S2*) where S1 and S2 are the two single look complexes. And I know this calculation uses a maximum likelihood estimator but why do you need to specify an estimation window and why cant the estimation window size be 1?
Thank you.
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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
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Mechanical contact stylus techniques are the traditional method of measuring the internal diameter (ID) of shafts. Bore gauge is a good example for this method. Now I am trying to use non-contact method and after researching about different non-contact techniques and the available equipment, I found confocal chromatic sensor very accurate (as low as 0.5-2 microns). I learned how to use it to find some GD&T features like run-out but I don't know how to find the bore size (internal diameter). The case study is explained below. Any suggestion is highly appreciated.
Geometry: A cylindrical shaft with internal diameter of 0.926" and length of 40"
Question: To find the size of ID by using confocal chromatic sensor.
Thank you
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Several
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While turning of titanium alloy Ti64ELI (manufactured by laser sintering ) by Single point diamond machining by very precise turning by Nanaform 200 CNC machine.It was observed that surface roughness incresed with the increase with cutting speed and surface roughness decreses with increase with feed rate. which is in clear contradiction with conventional trend . The surface roughness is recorded by correlation coherence interferometry(CCI) method. I am looking for the reasonable argument supporting the findings.
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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.
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Have you ever had challenges in measuring infinitesimal variations in the environment including 'in vivo' biological analytes? Microwave technology has proposed methodologies in the past few decades towards the compact, yet sensitive, sensors. While their relatively high-quality factor helps to resolve a wide range of variations, their sensitivity is limited by the constant presence of the host medium. The following article is laying out an interferometry approach to circumvent this issue for extremely sensitive measurements.
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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
Best regards
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I am using laser diode centered at 840 nm as the source. The experimental setup is similar to the figure shown below. The beam splitter cube splits the beam into reference and sample. The coating for all lenses and the beam splitter is for the specified wavelength. The objectives in both the arms are not coated for 840 nm wavelength but has transmission of 60 % at that wavelength.
When I image the sample on the camera, the reflection from the back surface of the beam splitter is prominent. Rotating the beam splitter deflects the beam on the objective but does not necessarily remove the back-reflection (ghost image) from the beam splitter.
How to get rid of back reflection?
Which beam splitters are generally used for Full-Field OCT or Linnik based interferometry systems? I have gone through few papers and they use the similar beam splitter as I use- Non-polarising cube beamsplitters and they don't face the ghosting problem.
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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.
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I need to study the surface topology of a specific polymer. Is there any method to study the surface properties of polymers using interferometry?
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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
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Hello,
I'm studying the CGH interferometry used on the test of large-departure asphere.
I want to make sure what is the maximum aspheric departure of the test surface that can be measured? what determines the maximum aspheric departure?Is it the CGH machining accuracy?
Does anyone know? We can have a discussion.Thank you!
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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.
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Hi,
I would like suggestions for a fast test for early detection of microcracks on an organic coating. In the past SEm was used but it is expensive and only a small area can be observed.
We are looking for a fast ( and cheaper alternative) to survey severl mm2 at a time for early detection of microcracks. Substrate is normally a metal ( steel, cast iron ) and the coating can be from 20microns to 100 microns thick.
someone suggested white light interferometry for this application, does anyone have experince with this technique? what resolution can we expect, how fast is it? ( is the equpment more accesble than SEM?
Could you suggest any other technique for this application?
Thanks in advance ,
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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
Best regards, Pierluigi Traverso
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Dear Colleagues,
Recently I had an argument with a colleague on whether the energy-transfer equations, and Beer's law specifically are applicable to smallish distances, specifically below the photone free pathlength. Both sides provided arguments, but, the discussion being during a coffee break, no citations.
Could you comment. Of special interest would be the citations on treatments of the cases when the lengths involved are much shorter than the corresponding free pathlengths.
A hundred years ago, when the difussion was a hot topic, this limit had no practical value. Now, when femtosecond pulses and low-coherence interferometry are widely used, this unresolved topic is back.
I suspect that it has been treated long time ago, probably around the time of Eistein and Smouluhovskii ... but I can't find citations.
Could you help?
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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.
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I have been using Michelson Interferometry to characterise the surface flatness of my glass cell. In the reference arm of my interferometer, I am using a mirror of surface flatness lambda/10. The wavelength I am using in this measurement is centered around 630nm.
One of fringe patterns I captured is shown in the imaged attached to this question.
I wish to reconstruct the surface of the glass cell through the interference fringes. Are there any existing computational techniques/opensource code to do so?
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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
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hello,
i am using cygwin. i have imported the snaphu in cygwin and it is running. it is showing some parameter variation like number of nodes in network, pivots, tree size. i have assured the the status of program using task manager of windows explorer. i am not getting how long it will run. it has been taken 48hrs already.
my system configuration is HP Z620, 24GB RAM, Windows8.1
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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
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I should find free SAR images ( Spaceborne or Airborne).
Especially I need complex SAR images and also StereoSAR images for same area.
So I can examine both interferometric and radargrametric algorithms' results.
Thanks.
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Please go through this website https://vertex.daac.asf.alaska.edu/# . SAR Sensors data are available in this website.
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This might sound like a simple/stupid question, but working in photoacoustics often requires substantial work in the form of choosing how to acoustically couple my acoustic sensor to my sample of interest.
Assuming I am using a transducer such as those in the link, what is my best bet for acoustic coupling to reduce bubble formation that is simple to set up, inexpensive, and repeatable?
Obviously, a lot of this depends upon the situation, but I'm interested in hearing what you use for this since I'm trying to figure out what would be easiest given my application. I've seen water coupling, gel coupling, and optical coupling (interferometry), but each of these methods has significant drawbacks (water coupling always seems to have bubbles unless I use a vacuum, gel is the same way, interferometry is expensive).
What do you use?
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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.
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Spectrometer+Si-CCD? Fourier-Transform Interferometry? Something else?
Wavelengthrange 500-800 nm, very low photon flux << 1 photon/s.
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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!
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Hi to all,
Consider the following scenario (shown in the attached file):
Two mutually coherent and collimated light beams intersect as shown, creating the depicted 'bright' and 'dark' stationary interference fringes (fig. 'A'). Suppose we insert a very thin (compared to the fringe width) and, ideally, perfectly conducting 'sheet' across, say, the central 'dark fringe'(fig. 'B').
It certainly appears as though we can "cut each of the light beams in two, across an impassable barrier", yet they will persist and continue to freely propagate! This appears to be the case both for 'classical' EM waves as well as quantum-optical wavefunctions. Of course, no infinitely thin and perfectly conducting sheet exists, but it does seem that this effect will remain sufficiently intact under realistic conditions. 
Is this possible??
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@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 . 
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It is well known that SAR (Synthetic Aperture Radar) interferometry is based on the SAR technology. How SAR can detect the deformation in three dimensions after earthquake happen? is it possible to measure the slip rate and fault parameters from SAR technology?
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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.
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Hi All,
I was wondering what laser source is suitable in deep-UV region for interferometry-based Raman spectroscopy? NeCu laser vs Argon ion? By the way, I would like to use laser source with excitation <250 nm.
Thanks
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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.
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I am doing the research work of the wavelength phase-shifting interferometry. When the plate thickness is thin, the parasitic stripes formed by the front and rear surface can not be separated, what is a good way to do?
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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.
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Relation b/w scratches and diffraction intensity and the methods to detect the scratch density?
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 I think with fast image processing techniques this work can be done.
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Recently I was reading the article"Lu B, Yang X, Abendroth H, et al. Time-average subraction method in electronic speckle pattern interferometry[J]. Optics Communications, 1989, 70(3):177-180." And I was wondering how could we get the equation(13) through the subtraction of equation(9) and (10) , and I have problem with the term of cos(2*x). Unfortunately, because of it is an article of 1989 and I could not find the author's email. I doubt there may be some mistakes in equation (13), and I don't know how to get the term of Icos[2(φor)]| ?
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Thank you very much, I will search the book from school library
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We are attempting  to estimate the Snow Depth by using Remote Sensing Methods. We found that one of the methods that is used for this purpose is Altimetry and using Passive microwave data.
Is this possible to estimate snow depth using SAR data like Sentinel-1 with the high resolution (20 meter for example)? or is there  satellite data or product that we can estimate snow depth with high spatial resolution?
Can we estimate snow depth with interferometry (by using for example different bands or images from two different dates)?
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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).
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For my masters project I need to extend an existing setup to be able to measure the phase of the recorded intensity field. My supervisor proposed to use an off-axis holographic method to obtain phase information of the field. Now my question is how do I stabilize the phase difference between the reference wave and object wave. For clarity I added a sketch of the setup
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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. 
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I'm working on a setup for digital holographic interferometry where I determine phase difference maps of objects in unloaded and loaded states.
I already applied a correction related to the sensitivity vector which originates from the difference in illumination and observation directions. The results are almost but not exactly right. Now I wonder if there's an additional correction necessary which compensates for the beam splitter cube between camera and object in lateral directions?
I'd be very grateful for any advice on this or on how to determine deformation from holographic phase differences in general.
The setup is simple: reference and object waves are combined through a beam splitter cube in front of the camera sensor. No phase shifting, just the phase difference before and after deformation.
Thanks in advance...
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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? 
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actually I am working on a project to monitor nonspecific t cell activation..
I have extracted RNA and using kit i got cDNA from last three months i am working to optimize human interferon gamma primer using conventional pcr but i fail to get any result.
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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..
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I met a problem on using the piezoelectric actuator to actively stabilize the homodyne interferometry to avoid the signal fading problem and to eliminate the experimental low frequency noises. The mirror is attached to the PZT actuator to reflect the reference beam.  A Proportional-Integral circuit  was designed , together with the PZT and homodyne interferometry, to  constitute the feedback loop. I doubt the following problems: 1.Does the hysterisis or linearity and creep effects of the PZT influence the  stabilization?  Should these effects be seperatedly compensated or not, because the PZT is part of the closed-feedback-loop. 2. Does the response time of the PZT and the circuit influence the stabilization? 3. I cannot stabilize the homdyne interferometry well, what other factors may contribute to the unlocking of stabilization ?   I do really appreciate your answers.
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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.
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How can I synthesise the Sparse antenna array using PSO, GA and DE techniques? I have to optimize the 2D Array factor.
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Hi Awan,
What do you mean by Optimise in the context of 2D-arrays ? 
Best of luck.
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I am using the SNAP processor to generate the DEM from the SENTINEL 1A SLC data. In the tutorial available (attached herewith), there comes a step called topographic phase removal (interferogram flattening). I have a doubt as this step is to be implemented only for calculation of the displacement phase as the removal of the topographic phase will remove the height from the interferogram leaving only with the displacement phase. So if I am deriving a dem I have skip this step and do it for estimating displacement (deformation) which by principle will be a two pass differential interferometry.
I would like to suggestions as to whether the interpretation I have provided above is correct and in that case what will be processing step for removing the displacement phase while generating the dem.
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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)
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I contacted Fisher Scientific about what the flatness of their fisherfinest microscope slides is, and they told me that they do not know that information.
I have deposited some nanometer films on these slides as substrates and I wanted to confirm some suspicions I had regarding these slides not being very flat, etc. based upon how they are made.
Does anyone have this information/an estimate of how flat they might be?
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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
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Which one of this level of processing for Satellite data ( COSMO SkyMed ) will be good for my study.And I am ordering STRIPMAP HIMAGE. Mostly, I will be using for DEM extraction, river cross section extraction, Landuse/landcover etc.
1. Level 0( RAW)
2. Level 1A( SCS) - Single Look Complex Slant
3. Level 1B( MDG) - Detected Ground Multi Look
4. Level 1C( GEC) - Geocoded Ellipsoid Corrected
5. Level 1D(GTC)- Geocoded Terrain Corrected
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In NEST-DORIS software
How to produce three pass interferometry "DInSAR" I need further information than existing in the software user manual 
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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.
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I am using Sentinel-1 TOPS SAR data for Himalayan Glacier. i have used Sentinel-1 Tool Box for interferogram generation. there is no step for phase unwrapping. SNAPU is the only way to unwrap the phase. but i could not understand how to unwrap using SNAPU.
Please tell me the phase unwrapping method for Sentinel-1 datasets.
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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
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I have read the recent paper from Abbott et al about the recent discovery of gravitational waves by the LIGO experience. I'm wondering: if gravitational waves are an evidence of a change in the spacetime structure, they also affect the measurement devices (I mean everything except the arms of the interferometer). In other words, would the possible impact on these devices modify the measurement results or even create false alarms? Was that taken into account in the data processing?
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Please, read this paper http://arxiv.org/abs/gr-qc/0501041
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Hello all,
I've come across a lot of information on several types of interferometers, but most of this information is quite scattered along the literature. I've been asking around if anyone knows of a good reference book on interferometry and the different types of interferometers  (such as Fabry-Pérot's, Mach's, Michelson's, Bath's).
Thank you in advance,
Alcides
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Dear Alcides,
you can try this book - " Optical shop testing" by Malacara.
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First of all I want to apologize for my english. I am not a native english speaker.
This question relates to the Fabry-Perot-Interferometer respectively the Fabry-Perot-Sensor.
In a lot of scientific papers it is mentioned that the analysis of the cavity length of the Fabry-Perot-Interferometer is accomplished with the help of white light interferometry. This mean a broadband light source with low coherence length is used. So the cavity length is much greater than the coherence length of the light. In my understanding interference and hence modulation of the light in this case is not possible because constant phase relation as a premise for interference is not given. But how is it still possible that interference occurs and the spectrum of the broadband light source is modulated?
I added a dissertation where a white light based Fabry-Perot-Sensor is used (Page 21).
Thank you in advance!
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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).
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When we use a reflective LC SLM for a self referenced interferogram, what are the parameters to determine the angle of tilt of the SLM? I read that angle of tilt also depends on the grating separation.
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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
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I want to know if we can create interferograms using two different SAR satellites? the satellites must have different orbit and phase?
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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.
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Trying to install Heterodyne Interferometry.
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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.  
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I am working on SAR interferometry with some TSX Stripmap mode images. I have some choices for "Processor Gain Attenuation" which are 0, 10 and 20dB but I totally have no idea about this value.
Could you let me know some suggestions?
Could you tell me which software is best for TSX interferometry processing? Thank you! 
Xuan
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I am looking for PM HNF fibers for a f-2f interferometer to detect the offset beat of a frequency comb oscillator (frep = 80 MHz, 1560 nm). The f-2f interferometer should be build all in fiber. Further I don't know yet how the dispersion/nonlinearity profile should look like to achieve peak powers at 1064 nm and 2128 nm within the supercontinuum.I have found companies such as Sumitomo and OFS. However, the MOQ and pricing is quite high. Are there samples or fibers from other manufacturers available which might suit this application ? Many thanks ! Sebastian
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Dear Sebastian:
I think the scheme (in letter "Operation of an optically coherent frequency
comb outside the metrology lab") wil help you.
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 I heard that the swept wavelength interferometry is used for a distributed sensing over ~km dynamic range. What kinds of tunable source is used for this kind of application? (linewidth, bandwidth, tuning rate ..etc)
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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.
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I am trying to find an implementation of the method described in: Fourier-transform method of fringe-pattern analysis for computer-based topogrphy and interferometry by Mitsuo Takeda et al ?
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Can the refractive index of the aqueous solution change with increasing pressure?
And how the pressure change may affect the behavior of the thermal gradient in the aqueous media?
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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.
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laser induced dielectric breakdown
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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. 
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looking to eliminate the etalon reflections. Need to know if there is a way to eliminate or remove the etalons in frequency domain and obtain a single pulse in the time domain?
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I think, this paper could be useful:
Improved sample characterization in terahertz reflection imaging and spectroscopy
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optical temperature measurement methods
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After forming an interferogram, phase filtering and phase unwrapping. The interferogram is geocoded. Now, how can I extract displacement information from the produced interferogram?
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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.
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when point source is placed near the surface of a glass plate of width 1.15 mm, I have got the fringes as shown in the figure attached. Rotating the glass slide to an angle of 10 through an axis perpendicular to the laser beam, the central bright fringe becomes dark due to change in its optical path length. How the central fringe is varying due to rotation is shown in the attachment.  I want to simulate how the fringe pattern is varying with the change in the phase difference between the beams on matlab, how should I proceed, please give your references/books/articles.....
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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. :)
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In geodetic applications, how can one use differential interferometry for crustal displacement monitoring?
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interferograms 
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for DInSAR processing but I encountered some problems in Phase Unwrapping of the produced interferograms.
These problems represented in installing and compiling SNAPHU "http://web.stanford.edu/group/radar/softwareandlinks/sw/snaphu/"
on Linux Ubuntu
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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...
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I know Michelson Interferometry for the  temporal and coherence length measurements and Shack-Hartmann wave front sensor for the spatial coherence detection. What else do you suggest?
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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.
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I want to record the interference pattern at the focal plane of the pre-defined field.
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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.
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Is there any news on the timeframe for a global availability of SRTM-1 (1 Arc-Second) data?
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yes! it will be released this year and will be finished next year. see her for more details: http://www.digital-geography.com/announcement-realease-worldwide-high-resultion-srtm-data-30m/#.VEgDPq0vkwc
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I use a photodiode light in my setup (FTS Spectrometer). I want to align the beam for the best visibility.
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Of course, all depends on the detailed optical layout of your interferometer but to previous comment of Patrick Balzerowski I can recommend to read about the white-light interferometers. The paper "Characteristics of synthesized light sources for white-light interferometric systems" (in Optics Letters, 1993, v 18, n 22, p 1884) could be an example.