Question

Q5) Optical cavity. Frequency spacing between succesive modes of a cavity is given by JAvl c/(2nL). a. Use c-λν to show that wave length spacing between succesive modes of a cavity is lan-R/(2n L). b. An Argon gas laser has a gain region of 1.0 m length. The light emission by Argon atoms covers a frequency range of 3.3 GHz. The index of refraction of Argon gas is 1. How many modes can lase simultaneously in this Argon laser? c. A GaAs edge-emitting laser diode has a cavity length of 400.0 um and a center operating wavelength of 860.0 nm. If the light emission spans a range of 3.2 nm, how many modes can lase simultaneously?

Answer 1

a) v = c/lambda = > Delta v = c(-1/lambda^2 Delta lambda) Vertical-bar Delta v Vertical-bar = Vertical-bar 1 - c Delta lambda/lambda^2) Vertical-bar = c Delta lambda/lambda^2 c/2 nL = c Delta lambda/2 lambda^2 = Delta lambda = lambda^2/2 nL (B) Number of modes m = Delta v times 2 nL/c m = 3.3 times 10^9 times 2 times 1 times 1 m/3 times 10^8 = 22 m = 22 (c) m = Delta lambda/lambda^2 (2 nL) = 3.2 times 10^-9/(9600 times 10^-9)^2 times 2 times 400 times 10^-6 1 m = 3