Laser coherence linewidth measurement based on deterioration of coherent envelope

The laser linewidth represents a pivotal parameter for assessing laser energy concentration and coherence, thereby exerting a significant influence on aspects such as detection range, measurement resolution, and signalto-noise ratio in the domain of laser precision measurement technology. Historically, laser linewidth measurement has predominantly relied upon evaluating energy distribution width within the frequency domain. However, this approach does not provide a direct assessment of laser coherence. In the present study, we introduce the novel concept of "coherence linewidth" as a means to directly quantify laser time-frequency coherence. This concept is based on the coherent envelope generated through delayed self-heterodyne detection. In our proof-ofconcept experiment, we derive the coherence coefficient via Fourier transform of the partial coherent envelope, subsequently enabling the measurement of the coherence linewidth of the laser. Notably, the measured coherence linewidth falls between the traditional integrated linewidth and the intrinsic Lorentzian linewidth. This observation suggests that the coherence linewidth is less susceptible to the influence of low-frequency 1/f noise. The concept of coherence linewidth presented herein may serve as a promising method for the direct characterization of coherence in narrow linewidth lasers.