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Aurora_b
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- Homework Statement
- Why do we get circular fringes in Fabry-Perot Interferometer experiments?
(This is not really a homework but a doubt I am not able to find an answer to)
- Relevant Equations
- The single beam produces multiple coharent beams in the interferometer, and the emerging set of parallel rays are brought together at some point in the focal plane of the converging lens . The nature of the superposition at P is determined by the path difference between successive parallel beams; taking the refraction index for air as 1, the condition for brightness is
2t cos(theta)=m*L
where t= etalon space
m= integers: 0,1,2.....
L= wavelength
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 the beam hits the mirror, a portion of the light is transmitted. So we get a multi beam interference but I am having a difficulty understanding why the interference pattern is circular. In Newton's Rings the shape of the thin film was responsible for the circular fringes but here, the mirrors are parallel the air film is like a cuboid then what is causing the circular fringes?