The Everise LSR Laser Linewidth Tester HJ-LSR-1001 is a versatile instrument for measuring, analyzing and monitoring the frequency noise of lasers in real time. The laser can be accurately characterized in real time, which is used to study the cause of optical frequency fluctuation in the accurate analysis of optical frequency noise characteristics of laser source. By combining the system's unique approach with the key visual X-series signal analyzer, it is possible to capture optical frequency noise signatures as power spectral densities.