Question

A helium-neon (He-Ne) laser has a gain bandwidth (defined as the frequency interval over which the laser gain equals or exceeds the minimum threshold for gain) given by ΔνG=2.5ΔνG=2.5 GHz, centred on λ=633λ=633 nm emission wavelength.

a)

Determine the maximum length of the He-Ne resonator when only one resonant axial mode can oscillate at any given time. (cm)

b)

By what length must the resonator be changed in order to tune the frequency of this He-Ne (i.e. with one resonant axial mode) over its entire gain bandwidth? (nm)

[HINTS: the length and frequency changes are both small compared to the length and frequency respectively. Try differentiation of the standing wave condition in a resonator. Your answer should be positive]

Answer 1

(a) 316.5 * 10^(-7) cm