Systematic analysis of correlated self-heterodyne method for intrinsic linewidth measurement

The correlated self-heterodyne method demonstrates significant advantages over conventional delayed self-heterodyne beating techniques for Hz-level intrinsic linewidth measurement. This innovative approach achieves superior performance through significantly shorter delay fiber lengths while maintaining exceptional versatility in measuring lasers at specialized wavelengths. In this work, we achieve intrinsic linewidth measurement deviations better than 2.5 % from sub-Hz to sub-kHz scales at a cost of $30k when compared to a $300k commercial linewidth analyzer. Furthermore, we systematically investigate and quantify the critical parameter boundaries, including the length of delay fiber and the sampling time of oscilloscope, governed by laser coherence properties. We also apply this method to specialized wavelength, such as 510 nm, which has a wide range of applications in quantum precision applications, and the intrinsic linewidth is 14.45 Hz. Our work establishes a robust framework for narrow-linewidth laser metrology, supporting advancements in precision optics and quantum technologies.