What is Fabry-perot: Definition and 23 Discussions

In optics, a Fabry–Pérot interferometer (FPI) or etalon is an optical cavity made from two parallel reflecting surfaces (i.e.: thin mirrors). Optical waves can pass through the optical cavity only when they are in resonance with it. It is named after Charles Fabry and Alfred Perot, who developed the instrument in 1899. Etalon is from the French étalon, meaning "measuring gauge" or "standard".Etalons are widely used in telecommunications, lasers and spectroscopy to control and measure the wavelengths of light. Recent advances in fabrication technique allow the creation of very precise tunable Fabry–Pérot interferometers. The device is technically an interferometer when the distance between the two surfaces (and with it the resonance length) can be changed, and an etalon when the distance is fixed (however, the two terms are often used interchangeably).

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  1. Daniel Petka

    I Can a single photon of a single frequency pass through a FP cavity?

    I was watching this amazing video about FP cavities and the creator mentioned that a single photon shouldn't pass through that cavity. Only multiple photons can. This doesn't make sense to me. The cavity works thanks to interference and single photons still interfere with themselves, so...
  2. Daniel Petka

    I Does a Fabry Perot cavity charge in discrete steps?

    I'm trying to understand the Fabry Perot interferometer and came across this amazing video. Basically it all comes down to adding E-fields together with each of them being delayed by the cavity round trip time. In the extreme case, either they all interfere constructively at the second mirror...
  3. dykuma

    I Fabry-Perot Interferometer mirrors

    I am trying to build a Fabry-Perot interferometer to make some narrow band filters, and I was wondering if anyone can go into the specifics of whether there's anything special about the types of mirrors used in construction. I started by trying to see how hard it really is to make one on my...
  4. B

    Correct Angle for FSW in Fabry-Perot Interferometer

    Sorry for the lack of formatting, I'm in a rush to write this before I go pick someone up from work. My question is what is theta1? Is it 45 degrees because that's the angle the light hits the boundary of the plate to the n1 medium? Or is it 0? It seems like it should be 45 but there's an...
  5. J

    Coupling of resonant modes in a 1D Photonic Crystal

    In 1D Photonic crystals, a defect can be introduced to create a defect/resonance mode and enable transmission. At first considerations, the thickness of the single defect layer determines the transmission frequency. Moreover, if it is a half-wavelength layer it will enable a resonance condition...
  6. U

    Methods for capturing a Fabry-Perot Interference Pattern

    I'm planning on doing an (undergraduate-level) experiment to study Zeeman Splitting in Cadmium. There's no complete set of instructions for the lab, but after seeing the materials, it appears that I will attempt to use a cylindrical Fabry-Perot Etalon to resolve the wavelength differences...
  7. M

    I Gaussian beam in a Fabry-Perot interferometer

    Hello I am reading some introductory laser cavity stuff and I am a bit confused about the existence of gaussian beams in the Fabry-Perot interferometer. If you solve the stability condition for a cavity (i.e. asking for the q parameter to reproduce itself after one round trip) you get that in...
  8. Aurora_b

    Circular fringes in a Fabry-Perot Interferometer

    Fabry-Perot Interferometer contains an etalon(an optical cavity created by 2 partially reflective mirrors placed parallel to each other separated by a small distance). When light enters the etalon it gets reflected back and forth between both the mirrors, being partially reflective, every time...
  9. H

    I Understanding the transmission of an etalon

    Hi there, I have a question concerning the etalon (One would think that I find an answer for this in every standard physics textbook or this forum, but I actually did not): An etalon can be built from a solid block of glas (for example) with dielectric high reflectivity coatings (let's say R=99...
  10. 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.
  11. A

    Mutilple beam reflection question in Fabry-Perot cavity

    Homework Statement Just having some trouble with a question about Fabry-Perot intereferometers. Here's the question: a) Consider a beam of light undergoing multiple reflections in a Fabry-Perot cavity between two surfaces, both with reflectance R, and with no absorption. Homework Equations...
  12. R

    Fabry-Perot Etalon Design: Resolving 514 nm Laser Modes

    Homework Statement Design a Fabry-Perot etalon that can resolve the longitudinal modes of a 514 nm laser. The laser is 2 m long.The FWHM of the gain spectrum is 8.8 GHz. What value of d (separation) and R (reflectivity) must be chosen? Homework Equations Finesse coefficient is...
  13. S

    Fabry-Perot Cavity: Frequency Separation Explained

    As "refresher assignment" for the new semester I have been given a selection of very short questions, the only one I am having trouble with is the followng: QUESTION An air-spaced fabry perot consists of two exactly parallel reflecting surfaaces, separated by a distance of 1 cm. What is the...
  14. H

    Fabry-Perot interferometer

    Homework Statement A Fabry-Perot interferometer has spacing d = 2 cm between the glass plates, causing the direct and doubly reflected beams to interfere. As air is pumped out of the gap between the plates, the beams go through 23 cycles of constructive-destructive-constructive interference...
  15. N

    Tunable Fabry-Perot interferometer

    Hi all. I am trying to understand how a tunable Fabry-Perot interferometer works. This is what I have understood so far: An etalon is placed inside a pressure vessel, and the pressure inside this chamber is changed. Apparently, this changes the "effective optical path length" between the two...
  16. R

    Fabry-Perot Etalon Homework: Determining Wavenumber Separation

    Homework Statement A certain spectral line is known to consist of two equally intense components with a wavenumber separation less than 20 m^-1: The Fabry-Perot fringes produced by this line are photographed, using a plate separation of 25 mm. The diameters of the smallest rings are found...
  17. H

    Path difference in Fabry-Perot etalon

    Hi I'm trying to understand how the Fabry-Perot etalon works for an experiment regarding the Zeeman effect. Looking at the image could anyone tell me why the path difference in the etalon is \Delta l = 2t \cos{\theta}? In my head, the path difference is \Delta l = 2t/\cos{\theta}, in other...
  18. T

    Solving Fabry-Perot Problem: Increase L by \lambda/2 to Scan FSR

    Homework Statement Show that it is only necessary to increase the distance L between two mirrors of a Fabry-Perot cavity by a distance \lambda/2 to scan the transmission peak over a range of one FSR Homework Equations The Attempt at a Solution D=2L*sqrt(1+v^2/c^2)
  19. Math Jeans

    Fabry-Perot interferometer diffraction

    Homework Statement A Fabry-Perot interferometer consists of two parallel half-silvered mirrors separated by a small distance a. Show that when light is incident on the interferometer with an angle of incidence \theta, the transmitted light will have maximum intensity when a = (\frac{m \cdot...
  20. C

    Fabry-Perot Interferometer as Principle for Bris-Minisextant

    I recently came across the Bris-Minisextant(wwwdotcassens-plath.de/catalog_web/096e_webdothtml) while researching sextants in general. While not truly a sextant in the conventional sense the device caught my attention and I started looking into what might be its underlying physical principle...
  21. cepheid

    Fabry-Perot Cavity: Energy and Round Trip Phase Dynamics

    Hi, I know this is dumb question, and I should be able to figure it out and move past it, but I can't. The optics book I have begins its treatment of Fabry-Perot cavities by considering the case of an undamped optical resonater (perfectly reflecting mirrors). Here's a quote from it: If that...
  22. L

    About observing the mewcury spectrum with a Fabry-Perot interferometer

    [SOLVED] About observing the mewcury spectrum with a Fabry-Perot interferometer Hello! I've been trying to observe the interference fringe pattern from a mercury discharge tube, but the pattern has not already shown up. I simply don't understand what I'm doing wrong. The first thing I did...
  23. S

    Fabry-Perot Interferometer: Energy Conservation

    Homework Statement This is regarding a Fabry-Perot Interferometer with identical mirrors: If you shine a beam of light on a 99% reflecting mirror, 1% goes through and the other 99% is reflected. But if a second mirror is placed behind the first one, where there is only 1% of the light...