Fig. 1. Longitudinal Zeeman dual-frequency laser

Fig. 2. Transverse Zeeman dual-frequency laser

Fig. 3. Strong mode competition curves at 20 MHz frequency difference: laser intensity versus cavity long tuning

Fig. 4. Laser with frequency splitting caused by intra-cavity stress birefringence element,and the force is applied to the window plate

Fig. 5. Laser with frequency splitting caused by intra-cavity stress birefringence cavity mirror

Fig. 6. Stress birefringence dual-frequency laser in which the spring is fixed on the stress birefringence cavity by spring-loaded barrel hoop

Fig. 7. Relationship between the width of frequency domain and laser frequency difference

Fig. 8. Internal engraving stress dual-frequency laser. (a) Laser structure; (b) cross-section of laser output mirror

Fig. 9. Kovar-glass assembly-internal sculpting stress dual-frequency laser (provided by Beijing Leice Technology Co., Ltd.)