# Calculate Fringe Separation in Fabry-Perot Etalon

• janrain
In summary, the problem involves using a spectrometer with one half of the slit illuminated by mercury light and the other half by white light through a Fabry-Perot etalon. In the wavelength range of 4000 to 5000 angstrom, 20 fringes are observed in the continuous spectrum. The task is to calculate the plate separation of the Fabry-Perot etalon, which can be done by using the formula and information provided in the link provided.
janrain
problem:
in a spectrometer, one half of the slit is illuminated with mercury light and 2nd half illuminated with white light through a fabry-perot etalon. in the wavelength range of 4000 to 5000 angstorm , 20 fringes are observed in the continuous spectrum.
calculate the plate separation of the fabry perot etalon.

i don't know how to proceed. don't know the formula/what needs to be done to derive it.

janrain said:
i don't know how to proceed. don't know the formula/what needs to be done to derive it.

Read the section on the Fabry-Perot Etalon here

http://electron9.phys.utk.edu/optics421/modules/m5/Interferometers.htm

Save this link for a nice basic description of other interferometers.

The problem is telling you that there are 20 different wavelengths between 4000 and 5000 angstroms that will give constructive interference. It sounds like your case has and air gap between two plates, and you can assume very small angle.

thanks a lot. that helped.

## What is a Fabry-Perot Etalon?

A Fabry-Perot Etalon is an optical interferometer consisting of two parallel partially reflective surfaces, typically made of glass or other transparent materials. It is used to measure the wavelengths of light, as well as to separate and analyze different colors of light.

## How is Fringe Separation calculated in a Fabry-Perot Etalon?

The Fringe Separation in a Fabry-Perot Etalon is calculated using the formula Δλ = λ2/2d, where Δλ is the difference in wavelength between two adjacent fringes, λ is the wavelength of light, and d is the distance between the two reflective surfaces. This formula is based on the interference pattern created by the etalon.

## What factors affect the Fringe Separation in a Fabry-Perot Etalon?

The main factors that affect the Fringe Separation in a Fabry-Perot Etalon are the distance between the two reflective surfaces, the refractive index of the material used, and the wavelength of light passing through the etalon. Any changes in these factors can alter the Fringe Separation and the overall performance of the etalon.

## Why is Fringe Separation important in a Fabry-Perot Etalon?

Fringe Separation is important in a Fabry-Perot Etalon because it allows for the precise measurement of wavelengths of light. By accurately determining the Fringe Separation, scientists can analyze and identify the different colors and wavelengths present in a beam of light, which is essential in fields such as spectroscopy and telecommunications.

## Are there any limitations to using Fringe Separation in a Fabry-Perot Etalon?

Yes, there are a few limitations to using Fringe Separation in a Fabry-Perot Etalon. One limitation is that the etalon can only accurately measure wavelengths within a certain range, known as the free spectral range. Additionally, any imperfections or defects in the reflective surfaces can affect the accuracy of the Fringe Separation measurement.

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