What is Interferometry: Definition and 39 Discussions

Interferometry is a technique in which waves are superimposed to cause the phenomenon of interference, which is used to extract information. Interferometry typically uses electromagnetic waves and is an important investigative technique in the fields of astronomy, fiber optics, engineering metrology, optical metrology, oceanography, seismology, spectroscopy (and its applications to chemistry), quantum mechanics, nuclear and particle physics, plasma physics, remote sensing, biomolecular interactions, surface profiling, microfluidics, mechanical stress/strain measurement, velocimetry, optometry, and making holograms.Interferometers are devices that extract information from interference. They are widely used in science and industry for the measurement of microscopic displacements, refractive index changes and surface irregularities. In the case with most interferometers, light from a single source is split into two beams that travel in different optical paths, which are then combined again to produce interference; two incoherent sources can also be made to interfere under some circumstances though. The resulting interference fringes give information about the difference in optical path lengths. In analytical science, interferometers are used to measure lengths and the shape of optical components with nanometer precision; they are the highest precision length measuring instruments in existence. In Fourier transform spectroscopy they are used to analyze light containing features of absorption or emission associated with a substance or mixture. An astronomical interferometer consists of two or more separate telescopes that combine their signals, offering a resolution equivalent to that of a telescope of diameter equal to the largest separation between its individual elements.

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  1. S

    I Subtractive mode intensity interferometry?

    In the Hanbury-Brown and Twiss (HBT) family of experiments, they multiply the intensity signals from two detectors. Instead, what if we subract the signals? In this case, we should see the RMS type noise addition when the detectors are far apart, decreasing to a null when the detectors are...
  2. zinn

    I Separation angle between pulsars detecting Gravitational Waves

    I’m trying to understand the Hellings and Downs curve that is being used to argue for the existence of a gravitational wave background ([NANOGrav article][1]). How can it be that the angle between two pulsars is the only variable that determines if the gravitational waves will interfere...
  3. T

    New Master Student _ Interested in Optics Metrology

    Hello Physics Forums! I am a new member of our community. My background is in Mechanical Engineering, but I am currently conducting research in the field of Optics Metrology. Specifically, I am using Interferometry to measure distance and surface profiles, applying this in semiconductor...
  4. B

    B Interferometry: Photons Needed for Interference Pattern

    If you have, say, a two-mirror interferometer that is producing an interference pattern, how many photons are interfering? Two, or just one?
  5. Nijiro

    I Two-photon Stimulated Raman Transitions

    Hello everyone! I don't know much about quantum physics. I'm an amator, but I want to expand and deepen my knowledge in quantum. So, I decided on the Quantum Gravity Gradiometer to be the subject of my supervised personal initiative work. But I'm currently stuck with many things among which are...
  6. K

    I Confused about Ramsey interferometry

    Hello! Assume we have a 2 level system with the frequency between the 2 levels ##\omega_0## and ignore the lifetime of the upper state. In order to measure the transition frequency using Ramsey technique, you apply 2 ##\pi/2## pulses separated by a time ##T##. We have that the probability of...
  7. mhsjx

    I What'wrong in this argument? (Atom/Photon interferometry)

    First, we can think a MZ interferometer as a combination of two beamspliter and a phase shifter(from MIT course "Atomic and Optical Physics II", the paper is "Quantum-mechanical noise in an interferometer"), which evolution matrix is B = {{1,-i},{-i,1}},B dagger and P ={{1,0},{{0,exp{i\phi}}}...
  8. W

    I Stern-Gerlach "interferometry"

    Suppose we have a state ##|\psi\rangle \sim |\uparrow z\rangle + |\downarrow z\rangle## passing through a Stern-Gerlach magnetic field oriented in the ##\hat{z}## direction such that ##|\uparrow z\rangle##'s are pulled up and ##|\downarrow z\rangle##'s are pulled down. Then suppose we place some...
  9. D

    Interferometry (testing of optics)

    Hi all, I'm a mechanical engineer who has been dumped into optical metrology at work without anybody much more knowledgeable than myself to help me out. A previous mentor who left recently (who was our optical expert) always told me when measuring wavefront error of optics to "tilt-out the...
  10. L

    MATLAB Can I know the reconstruction of phase shift interferometry in Matlab

    I want to know the reconstruction of phase shift interferometry by angular spectrum method in matlab
  11. W

    Interferometer Considerations: Arm Lengths and Vibration Noise

    Homework Statement Hi all, I need some help regarding the following 2 problems. 1. i) Why must we ensure that interferometer arm lengths ##L_1, L_2## are approximately equal? ii) Is it also necessary for the distance from the beam-splitter to the laser, or the distance from the...
  12. B

    Relationship between interference and arm length in MZI

    A question about the Mach-Zehnder interferometer. My understanding is: If its two arms are equally long, there is destructive interference in one output and constructive interference in the other output. So, the intensity of light detected at the first output should be 0% and at the second...
  13. T

    Transmission and reflectivity in a Michelson interferometer.

    Homework Statement Sketch and explain the operation of the Michelson interferometer. How is the transmission of the interferometer modified if the amplitude transmission t and reflectivity r of the partially-reflecting beamsplitter are not equal? What happens to the fraction of light that is...
  14. A

    B How does LIGO measure gravitational waves

    I'm aware that the LIGO system uses interferometry but I'm confused how it works in this case. Do they test both beams of light? Or do they use one beam to test the wavelength of the other and see the difference? Also it is sensitive up to 10 e-18 meters, is that for the change in wavelength or...
  15. O

    Ramsey fringes - free oscillations

    i´ve got a question concerning Ramsey interferometry and fringes. Consindering the case we have 2 pi/2 pulses as usual. For this case it is easy to calculate the mean value of the Bloch component w by applying a rotation matrix, say rotating around the Bloch component v. Then applying a rotation...
  16. Charles Link

    Insights Fabry-Perot and Michelson Interferometry: A Fundamental Approach - Comments

    Charles Link submitted a new PF Insights post Fabry-Perot and Michelson Interferometry: A Fundamental Approach Continue reading the Original PF Insights Post.
  17. S

    B Interferometry on photodetector

    Hello! I am trying an interferometry experiment using the Michelson Morley experiment. I managed to obtain the interference pattern on a screen, but I want to use an photodetector and I am not sure what should I obtain. As I know, the oscilloscope shows the intensity of the light, so if I modify...
  18. L

    I Closure Phase - Interferometry - Recurrence Relation

    Hello, I'm trying to calculate a recurrence relation of the phases of 3 telescopes in a closure phase. Usually in a stellar interferometer we have 3 telescopes, located in a triangle, measuring intensity of light in 3 points on a far field plane. I found an article, describing how the phase is...
  19. naima

    Interferometry of distant sources

    When you try to get fringes, the worse is when the source is extended and the light has a large energy spectrum. With a star, the source seems pointlike. Is there another advantage as regards with bandwidth?
  20. faofao

    Difference betweend Fizeau and Wedge Interferometry

    Hey everybody, I have a question concerning the difference (if any) of the Fizeau and Wedge Interferometry. I am currently writing my thesis on a project which uses a glass wedge with air in between. This concept is fairly well discussed and background of this can be found in several textbooks...
  21. naima

    A question about interferometry (Zeilinger paper)

    Hi all, I am reading this Zeilinger http://www.univie.ac.at/qfp/publications3/pdffiles/1996-04.pdf Look at fig 1. There are four detectors D1 D2 D3 and D4. When one of these detectors click, what does it mean? what is the state it detects? The author gives a formula in the first page. P13 = (1...
  22. marcus

    Exploring Quantum Gravity Phenomenology: Experiments with Interferometry

    Sabine Hossenfelder recently wrote a blog post containing this parenthetical remark: "(I had meant to write a summary of which possible experiments for quantum gravity pheno are presently being discussed and how plausible I think they are to deliver results, but I got distracted by Dyson’s above...
  23. D

    Optical tweezers, QPD back focal plane interferometry vs imaging

    Hello, I use a 10x infinity objective as a condenser in a optical trap setup. The collimated forward scattered light is then focused with a 40mm lens onto a QPD. This is the imaging techqnique. There is also BFPI, and I am not clear on this method. My understanding is that I need to image the...
  24. R

    Ideas for Interferometry project? - Help Needed

    1. Hi! Sorry, was unsure whether this was the right place to post, new here. In any case, I need a bit of help with a project a friend and I are working on. First of all, it's a pretty large project, supposed to take us approx 100 hours. We're in the last year of Swedish high school, only...
  25. S

    Radio Astronomy. Baselines and Fringes, Interferometry

    As I understand Interferometry, a baseline does not refer to the distance between two RA scopes. It's the distance between two line of sites for each scope. They are parallel, when directed at the same object. Suppose we have two scopes at two stations that are some distance apart, say...
  26. W

    Nuetron Interferometry in Ballentine

    In chapter 5 of Ballentine, he talks about neutron interferometry performed by Zeilinger et al (page 141). I am confused by this discussion as he starts talking about the neutron beam as a wave propagating in real space, something that he himself strictly warns not to do. What is going on?
  27. S

    Remote-Sensing Quantum Hyperspace by Entangled Photon Interferometry

    http://arxiv.org/abs/1101.2223 Abstract Even though ideas of extracting future-related, or Faster-Than-Light (FTL) information from hyperspace using quantum entanglement have generally been refuted in the last ten years, in this paper we show that the original 'Delayed Choice Quantum...
  28. C

    Quantum interpretation of Ring Laser Interferometry

    I have a question about Ring Laser Interferometry. A couple of years ago I contributed some text and several pictures to the http://en.wikipedia.org/wiki/Sagnac_effect" . Ever since I have been curious about the quantum interpretation of Ring laser interferometry. The special thing about...
  29. I

    Distance measurement by means of optical interferometry

    Hi, I have been assigned to a new task in my job where I have to investigate on measuring the distance to an object by means of optical interferometry (Michelson interferometry). I have been looking for info on the subject but have not been really lucky. I have been able to obtain the...
  30. P

    Laser interferometry and the search for gravitational waves

    When viewing the light coming from distant galaxies, it is my understanding that there are 2 redshifts occurring, the doppler effect from the galaxies' peculiar motions, and the cosmological redshift from space itself expanding. For the cosmological redshift, I visualize a square of space...
  31. M

    Light interferometry as described in Thorne's black holes and time warps ?

    light interferometry as described in Thorne's "black holes and time warps"? hello, maybe someone who read the book can help me with this, but i'll give all the information so that even someone who hasn't read it can understand. At page 383 and following, and at fig. 10.6 and box 10.3, Thorne...
  32. K

    Looking for Help with Laser Interferometry and Collimating Lenses?

    Hi all Im doing work on laser interferometry for my final project,just wondering if there are any experts or experienced people in this field here,thanks much!
  33. M

    Intro Physics Lab Interferometry Question (Fabry-Perot vs. Michelson)

    Homework Statement The Michelson interferometer can be used to measure extremely small distance scales. What is the smallest distance scale that can be measured? What uncertainty is associated with this? What is the smallest scale that can be measured by the Fabry-Perot...
  34. M

    Need Help with Michelson Interferometer Setup?

    Hey there, I'm doing a Michelson Interferometer for my final Physics project, and my partner and I are having some difficulties. We have our beam splitter set up 45 degrees from the light source (a simple red laser) and 2 mirrors set up in such a way that the one directly across from the beam...
  35. M

    Polarization in Interferometry

    I'm working on a laser-based holographic interferometry system. Basically, I produce a linear fringe pattern with a Mach-Zender style interferometer setup. Then when I put a transparent sample in one of the beam pathways (cell cultures), I can determine the phase offset produced based on the...
  36. J

    Calculating Optical Interferometry Telescope Resolution

    I can't find any useful page which explains in detail how to calculate the equivalent resolution of an optical interferometric telescope. I found out, after LONG search, the formula to calculate standard-telescope resolution: Resolution (Km) = 5,5680 * 10^-4 * Distance (Km) / diameter (mm)...
  37. S

    Atom Interferometry for Nuclear Reactions

    Recently, we've heard about research into storing anti-hydrogen as a BEC. Atom lasers are touted for their potential to make ultra-precise measurements, including at the quantum scale, because of their small DeBroglie wavelengths in comparison to light. Once, I emailed Dr Wolfgang Ketterle...
  38. N

    MATLAB Phase-stepping Interferometry & MATLAB

    Homework Statement I am given 4 files containing the intensities of a fringe pattern with phase-steps of \pi/2 . I need to do a mesh plot (on MATLAB) of the intensities and phase. Homework Equations I=A+Bcos(\phi) The Attempt at a Solution I came up with the following...
  39. Hans de Vries

    Talbot Lau interferometry of carbon-70 fullerenes

    ==================================== Talbot Lau interferometry of carbon-70 fullerenes ==================================== I’ve looked at most of the documents published on these macroscopic quantum interference experiments of fundamental importance. These experiments seems to shift the...
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