Fig. 1. Experimental setup of the continuous wave single-frequency 1.5 μm laser based on unidirectional travelling-wave ring cavity

Fig. 2. Evolution of the pump beam. (a) Evolution of the pump beam passing through the beam coupling system and input couplers; (b) size of pump beams as a function of the position relative to the center of Er,Yb∶YAB crystal

Fig. 3. Measured thermal focal length of the sapphire-Er,Yb∶YAB-sapphire crystal as a function of the pump power

Fig. 4. Measurement results of the thermal focal length of BIG crystal. (a) 1.5 μm laser power as a function of incident pump power at different resonator lengths; (b) thermal focal length of BIG crystal as a function of the intracavity laser power

Fig. 5. Radii of laser waist as a function of the incident pump power at the center of laser crystal and in the tangential and sagittal planes, respectively. (a) L=150 mm; (b) L=170 mm; (c) L=180 mm

Fig. 6. Behaviors of the 1.5 μm laser. (a) Output power of 1.5 μm laser as a function of pump power; (b) transmitted intensity of the scanning F-P interferometer

Fig. 7. Power fluctuation of CW single-frequency 1.5 μm laser

Fig. 8. Measured intensity noise spectrum of CW single-frequency 1.5 μm laser