Expanding Continuous Tuning Range of a CW Single-Frequency Laser by Combining an Intracavity Etalon With a Nonlinear Loss

Combining intracavity etalon (IE) locked on a laser oscillating mode with a deliberately introduced nonlinear loss, the tuning range of a continuous-wave (CW) single-frequency laser is significantly expanded to transcend the traditional limitation of a free spectral range (FSR) of IE. Due to the action of the nonlinear loss, the frequency of laser oscillating mode can be continuously and smoothly tuned without any mode-hopping in a tuning range much larger than FSR of IE. We theoretically analyze the physical mechanism behind the influence of nonlinear loss on the tuning range expansibility of the laser and experimentally demonstrated the effectiveness of the presented method. By means of this method, the ultrawide continuous frequency scanning range of 222.4 GHz at 532 nm is implemented. The theoretical analysis and the experimental results are in good agreement.