Laser Linewidth Measurement Based on Amplitude Difference Comparison of Coherent Envelope

We present an amplitude difference comparison of coherent envelope method for accurately measuring the laser linewidth. The new method of comparing the contrast difference of the second peak and trough of coherent envelope to determine the laser linewidth is proved to be stable and has little error. The feasibility and the accuracy of the method have been confirmed theoretically and experimentally. Our method based on short delayed self-heterodyne interferometer can almost ignore the influence of the broadening spectrum induced by the 1/f frequency noise. Therefore, the method has the advantage of accurate detection for narrow or ultra-narrow linewidth.