Correct Angle for FSW in Fabry-Perot Interferometer

In summary, the question is about the value of theta1, which is the transmission angle. For normal incidence, theta1 is equal to zero as shown in the textbook example. This can be seen in the side view sketch or central black spot in the first picture.
  • #1
Blanchdog
57
22
Homework Statement
What are the free spectral range and fringe width in a Fabry-Perot Interferometer made up of two silver coated plates each with reflectance R = 0.9, transmittance T = 0.05, and Absorbance A = 0.05? The plate separation is d = 0.5cm with interior index n1 = 1. Suppose the wavelength being observed near normal incidence is 587nm.
Relevant Equations
FSR = wavelength^2/(2 n d cos (theta1))
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 example in the textbook that uses 0. Or is cos(theta1) imaginary? Thanks!
 
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  • #2
near normal incidence
For normal incidence this ##\theta## is zero. The central black spot in the first picture here . Make a side view sketch (or look further down :smile:) to see where ##\ \theta\ne 0\ ## comes in.

##\ ##
 
  • #3
BvU said:
For normal incidence this ##\theta## is zero. The central black spot in the first picture here . Make a side view sketch (or look further down :smile:) to see where ##\ \theta\ne 0\ ## comes in.

##\ ##
Ah thank you, I was getting tripped up because I knew ##\theta_1## was the transmission angle but couldn't figure out what it was, but if the light is at normal incidence then the transmission angle will be zero.
 

What is the Fabry-Perot Interferometer?

The Fabry-Perot Interferometer is a device used to measure the wavelength of light. It consists of two partially reflecting mirrors separated by a small distance, creating an optical cavity. Light enters the cavity and is reflected back and forth between the mirrors, creating an interference pattern that can be used to determine the wavelength of the light.

Why is the correct angle important in FSW in Fabry-Perot Interferometer?

The angle of incidence of the light on the mirrors in the Fabry-Perot Interferometer affects the path length of the light within the cavity. This, in turn, affects the interference pattern and the accuracy of the measurement. Therefore, it is important to have the correct angle to ensure accurate results.

What is the ideal angle for FSW in Fabry-Perot Interferometer?

The ideal angle for FSW in Fabry-Perot Interferometer is when the light is incident on the mirrors at a right angle (90 degrees). This allows for maximum path length and produces the most accurate interference pattern.

How can the correct angle be achieved in FSW in Fabry-Perot Interferometer?

The correct angle can be achieved by adjusting the position of the mirrors or using a precision angle measurement tool. It is important to ensure that the mirrors are parallel and the angle of incidence is exactly 90 degrees for accurate results.

What are the potential sources of error in FSW in Fabry-Perot Interferometer?

Potential sources of error in FSW in Fabry-Perot Interferometer include misalignment of the mirrors, imperfections in the mirrors, and fluctuations in the temperature or pressure of the environment. These factors can affect the angle of incidence and the interference pattern, leading to inaccurate measurements.

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