Questions tagged [interferometry]

Interferometry is the name for a class of measurement techniques based on the interference of coherent optical fields or other electromagnetic radiation. Generally, Interferometric measurements are extremely accurate, but can be difficult to perform. Common uses for interferometry are optical component metrology and stellar interferometry, although there are many applications.

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How does a Michelson interferometer work?

First off, a Michelson interferometer does work. It can measure tiny length differences. Here is a video showing one in action. I must have misunderstood how it works. Here's what I think is happening:...
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Why fizeau interferometers are much more popular than point diffraction interferometers for optical metrology?

If somebody wants to measure surface error of for example concave spherical surface - in most of the optical companies around the world Fizeau interferometer will be used, with relatively large, high-...
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How is VLBI delay calculated, practically?

I’m working on a research project wherein we are trying to solve a problem very similar to VLBI delay. We have two radio receivers, and we know their locations. We also know at what time one receiver ...
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How is interferometry used to measure distances?

I understand how a basic interferometer works, and how Michaelson used an interferometer to more-or-less disprove the “luminiferous anther”, but, analytically, how would one go about using an ...
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Etalon Produces Odd Interference Pattern

The other day I created an optical cavity with a first surface mirror and a beam splitter. Here’s a pic of the interference. Has anyone seen something like this. Is it common?
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Experiment involving a homemade Michelson stellar interferometer

I am in high school and for a research essay I am thinking of writing on the topic of Radio interferometry. My school has a Newtonian telescope and I was thinking of building a Michelson stellar ...
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Phase unwrapping in interferometry

I observed that in "interferometry" is used a process called phase unwrapped. This process can be done by using complicated algorithms but I was not able to found an example more simplistic. If somone ...
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Fabry-Perot Interferometer

let's consider a Fabry-Perot interferometer: Illumination is provided by a diffuse source, and its rays are focused towards the cavity by a lens. Inside the cavity there are multiple reflections and ...
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Why is the central fringe in Fabry-Perot inteferometer dark?

We know that when the beams have phase shift due to reflection, the central fringe would be dark. But in the Fabry-Perot interferometer, except the first beam, each beam reflects 2 times (external ...
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Can someone help me understand this nested Mach-Zehnder interferometer by explicitly writing down the photon states in each steps?

The inner interferometer is balanced and it is tuned to destructive interference toward the final beam splitter of the external interferometer. The external interferometer has beam splitters with ...
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Does a Michelson pattern have a maximum radius?

I'm studying the Michelson interferometer interference pattern and we have arrived in class - using some aproximations - to some expressions which state a relationship between the radius of the ...
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Mach-Zehnder interferometer vs Michelson interferometer

I am doing a project that is based on the Mach-Zehnder interferometer, and we're asked to compare the interferometer with Michelson's interferometer. I know the geometrical differences between the two,...
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Difference between gravitational wave detectors

There are a lot of different gravitational wave detectors and they all have their own wave period and frequency they operate at. This picture shows that The last three (pulsar timing, space ...
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Does an interferometer add or multiply together signals? Is it either?

I'm studying honours physics right now and have to get an understanding of interferometers, specifically in the context of astronomy and interferometer telescope arrays. However, I'm having some ...
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Are the two interference patterns at the output of an interferometer quantum entangled?

When an interferometer creates an interference pattern a second interference pattern is always created. The two patterns are opposites of each other. Knowing one pattern lets me accurately predict the ...
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What should I look for when purchasing a Laser diode with good coherence?

I want to purchase laser diodes that will work well for interferometry. I have been using inexpensive laser diode modules that I buy from of Amazon for 2 or 3 dollars each. For the most part they ...
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On the optical equivalent of the Michelson interferometer

This page claims that the Michelson interferometer below is equivalent to the optical system bellow. How can it be? Where did the beam splitter go? And in the second system we restrict the incident ...
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Why do fringes appear, as opposed to a simple spot, in a Michelson interferometer?

A simple Michelson interferometer is generally presented like the one bellow If we observes through the telescope, we see fringes like these Is it the lens of the telescope that form theses fringes? ...
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Would relativistic LIGO hear different chirp?

Imagine a binary blackholes merger about 100 Mpc away and LIGO's relativistic twin is orbiting Earth at close to speed of light, I wonder would both LIGO and its twin show different results? For this ...
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Michelson interferometer: beam division

so I'm working on the Michelson interferometer for a presentation, and I'm having trouble understanding how does the beamsplitter splits the incoming beam. Let's consider the incoming bean as a ...
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Why is electric field Fourier transformed to produce image in radio astronomy?

In radio interferometry, to get an image, the correlation of electric field observed in different antennas are Fourier transformed. This gives the "brightness function in sky coordinates". Why do we ...
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Confusion about how differences in potential make state kets rotate at different speeds

In Sakurai's book "Modern Quantum Mechanics" (2nd ed.) on page 133 he describes gravity-induced quantum interference. A mono-energetic beam of neutrons is split in two and brought together again. One ...
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Help with calculating uncertainty of refractive index for Michelson Interferometer?

I need help with calculating the uncertainty of the refractive index of air which has been obtained by the equation in this document: $$n_{\text{air,atm}}=(\frac{N}{P/P_{\text{atm}}})(\frac{\lambda}{...
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Sidebands, cavity tuning and detection in interferometric gravitational wave detectors

I know the basics of gravitational wave detection but struggle to put things together and view the whole picture of the signal path. Most of my knowledge refers to second generation gravitational wave ...
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Measuring sound waves with lasers

I've recently been learning about recording techniques for music production, and I was surprised to learn that there are only three types of microphones in wide use (dynamic, condensor, and ribbon), ...
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What observable(s) does a mirror operate on?

I'm reading this introduction to the Mach-Zehnder interferometer, and I'm confused about what the mirrors are doing. Suppose we're describing the path (upper / lower) and polarization (vertical / ...
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Michelson interferometer phase difference when both mirrors are equidistant?

Using the following image as a reference. Source Why is there a phase difference added in the following equation? $2d \cos \theta =m \lambda + \frac{1}{2} \lambda$ I read it is because the beam ...
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What does it mean to extract phase from interferograms?

I hear a lot extract the phase from the interferograms, I need to know what does it mean? and what is the significance of that?
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How does a single satellite like the upcoming BIOMASS use interferometry?

The future satellite BIOMASS, from the ESA, will supposedly use p-band frequency interferometry to detect changes in forests. By itself? How?
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Does the spectrum of two-beam interference also show an interference pattern?

I know when you interfere two beams you get an interference pattern with a fringe pattern of λ/(2*sin(θ/2)) in physical space. It seems that there must also be modulation of the spectrum. Is this ...
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Are interference patterns the basis for all other measurements of light frequencies and wavelengths?

The wavelength or frequency of monochromatic electromagnetic radiation is determined indirectly by calculations on the interference or diffraction pattern. These patterns are generated by gratings, ...
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Why does an interferometer with mirrors even work? [duplicate]

My understanding is being thwarted by something basic I am missing. One starts with a light beam that is split into two perpendicular paths. There are two light paths that travel some distance. The ...
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How do I obtain coherence length of a monochromatic laser with data about the visibility?

I am using a Michelson interferometer and have obtained data about the visibility. However, I am now having trouble knowing what to plot in order to find the coherence lenghth of the laser. I thought ...
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A common misunderstanding regarding which path information in a double slit and Mach-Zehnder interferometer?

I just can't get my head around this. What does he mean when he says that a hit at one of the detectors doesn't imply that the particle went though a certain path? He calls this the "separation ...
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Why don't (can't) astronomers take advantage of interferometry to the extreme?

Reading and watching from various sources (e.g: APOD, ESO videos, or Wiki), whenever interferometry is mentioned, it is also usually explained like this: An astronomical interferometer consists of ...
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Cause of difference of coherence distance between different light source

I was doing my first interferometry experiment today, and we had to calculate a certain beam's coherence length (the distance in which it behaves regularly). I was explained that different beams have ...
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Does frequency of light change in the LIGO interferometer arms?

There are a number of questions on the internet and on this site asking about how the LIGO interferometer measurement works given that the gravitation wave stretches both the length of the ...
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Is Sentinel able to obtain wave spectrum by interferometric Data?

I have recently read many articles on recovering wave spectrum from the AT-INSAR image spectrum (through interferometric images). However, it is not clear to me whether Sentinel is a viable option, ...
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What do fringe patterns have to do with VLBI?

I think I have fundamental confusions with how VLBI works. I don't know why: Resolution increases when incident rays meeting to a focal point from a farther separation along an axis perpendicular to ...
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Maintaining phase relationships and other general principles of interferometry

I have a few confusions with some basic principles of interferometry. Bob Campbell's So you want to do VLBI writes: Phase relationships among all points on the wavefront will be preserved ...
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LIGO test masses in free fall

I know that the LIGO test masses are considered to be in free fall. However, they are supported by pendula. I thought that free fall means the only acting force is gravity - doesn't the tension in the ...
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Fringes of equal inclination (Haidinger fringes) Why is the interference pattern circular?

From Hecht optics 5th edition: It says 'With an extended source, the symmetry of the setup requires that the interference pattern consists of a series of concentric circular bands centered on the ...
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Could the black hole photo be a gravastar?

Mazur-Mottola gravastars would in many ways appear identical to black holes. Does the new radio-photograph of M87* taken by the Event Horizon Telescope eliminate M87* as a gravastar candidate, and ...
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Unexpected wavelength jumps in a laser observed: a fundamental noise source in VCSELs?

I observed an unexpected signal while developing an interferometric sensor using a VCSEL laser. In order to debug this noise I designed the following device that converts minute changes in the laser's ...
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If two observers look at the same quantum object, will they see the same thing?

Let's say two observers, one at the North pole and one at the South pole, both observe the Moon. Will they see the same Moon, or a subtly different Moon? Intuitively it feels like they should see a ...
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Precise Event Horizon Telescope locations?

Presumably, in order to perform their interferometry, the Event Horizon Telescope correlator needs to know (i) exactly the time of an observation, which I understand is accomplished by timestamping ...
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Direct observation of Gravitational Waves via increased resolution

First, congrats to the event horizon team for the first photograph of a black hole. Not to downplay the significance of the photo, but it is a bit blurry. Still, it got me thinking. One might expect ...
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Why is the Standard Quantum Limit (SQL) in Interferometers added as that of mass $m$ and not $2m$?

We write $$(\Delta z)^2 = (\Delta z)_{PC}^2 + (\Delta z)_{RP}^2 + (\Delta z)_{SQL}^2$$ to indicate the contributions to the total error from photon counting error, radiation pressure error and the ...
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How much more precise would LIGO have to be?

The planets and a spinning black hole both drag their local frames and thus generate gravitational waves The amplitude should be proportional to the size of the celestial body, while the frequency of ...
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What is the meaning of this operator?

In interferometry with coherent light, the final output is differenced detectors. That is, $\left<N\right> = \left<N_1\right> - \left<N_2\right>$ where $N_i$ is the number operator ...

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