A plane air-spaced Fabry-Perot cavity has mirrors of power reflectance and spacing

PHYSICS · Subjective · Fermi University Physics · Optics & Photonics · Interference and diffraction · Interference and diffraction

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Problem

A plane air-spaced Fabry-Perot cavity has mirrors of power reflectance R=0.98R = 0.98 and spacing d1=5.00 mmd_1 = 5.00\,\text{mm}. Someone argues: 'if the spacing is doubled to d2=10.0 mmd_2 = 10.0\,\text{mm} with the same mirrors, the light makes more round trips before it leaks out, so the finesse doubles as well.' Compute the finesse, free spectral range and linewidth for both spacings and use the results to say what actually changes when the spacing is doubled. Take c=3.00×108 m s−1c = 3.00\times10^8\,\text{m s}^{-1}.

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