Genevieve Gutierrez, M.S. Candidate

Department of Physics 

A Comprehensive Study on the Use of Sub-coherent Self Heterodyne Linewidth Estimations

Advisory Committee Members: 

Yan Zhou, Ph.D., Advisory Committee Chair 

Bernard Zygelman, Ph.D., Advisory Committee Member

Joshua Island, Ph.D., Advisory Committee Member

Jan Pedersen, Ph.D., Graduate College Representative

Abstract:

The starting point for many precision spectroscopy labs is the acquisition cof a stable and narrow linewidth laser. Narrow linewidth lasers are desiredceither for high precision direct transition measurements or for their usecas a tunable frequency reference. The problem is that verifying the

linewidth is not often straight forward, especially as linewidths decrease. In the world of frequency metrology, the delay self-heterodyne technique has been one of the most reliable and accessible measuring techniques available to optical physicists, due to the low cost of equipment and reproducibility of measurements. For years, the standard ways of doing self-heterodyne measurements have been using a long delay fiber that is longer than the coherence time of the laser, and either measuring the

instantaneous power spectral density or the noise power spectral density. The problem with using a long delay fiber is that they often heavily attenuate the light out, and thus require an amplification stage, and the fiber itself can introduce Brownian noise, which artificially broadens the spectrum. This paper argues that a short delay fiber below the coherence time provides much more reliable results. The purpose of this thesis is to provide comprehensive overview of how one goes about extracting the linewidth from the power spectral density of a sub-coherent self-heterodyne signal.