A tunable diode laser of linewidth MHz and vacuum wavelength nm produces two closely…

PHYSICS · Multi-part · Fermi University Physics · Optics & Photonics · Interference and diffraction · Coherence and statistical optics

Optics and Photonics, Ch Multiple-beam interference: thin films, multilayers and the Fabry-Perot etalon

Problem

A tunable diode laser of linewidth Δνlaser=5.0\Delta\nu_{\rm laser} = 5.0 MHz and vacuum wavelength 780780 nm produces two closely spaced lines separated by Δνlines=400\Delta\nu_{\rm lines} = 400 MHz. They are examined with a Fabry-Perot etalon of air gap d=5.00d = 5.00 mm and mirror reflectance R=0.80R = 0.80 on each face. ((a)) Find the coefficient of finesse FF and the finesse F\mathcal{F} of the etalon. ((b)) Find the free spectral range ΔνFSR\Delta\nu_{\rm FSR} and the instrument linewidth Δν1/2\Delta\nu_{1/2}. ((c)) Using the coherence length ℓc=c/Δνlaser\ell_c = c/\Delta\nu_{\rm laser} (Chapter 10), check that the laser's own coherence does not limit the etalon's performance. ((d)) Decide whether this etalon can resolve the two lines.

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