Influence of exterior acoustic noise on narrow linewidth laser measurements using self-homodyne optical fiber interferometer

Abstract

Spectral linewidth measurements of a HeNe laser were obtained by using a self-homodyne optical fiber Mach-Zehnder interferometer located in a vacuum controlled chamber. The data showed an apparent broadening of the highly-coherent laser linewidth from few hertz up to kilohertz with the change in the air chamber pressure, evincing an influence of external acousto-optic effects on the interferometer optical fiber. To support the results, a theoretical harmonic acoustic analysis was developed and then related to the correspondent interferometer phase noise spectrum measurements. Lorentzian approximations of the experimental laser apparent linewidth suggest that the interferometer was working in a quasi-coherent regime for all tested chamber air pressure