Fig. 1. Under varying pump powers: (a) the variation in single-pass and double-pass amplified laser energy; (b) the variation in the upper-state particle extraction efficiency of the Nd:YAG crystal for both single-pass and double-pass amplifications.

Fig. 2. Variation of the thermal focal length of the Nd:YAG crystal rod at different pump power levels.

Fig. 3. Relationship graph between the dimensionless aberration coefficient for a lens as a function of the lens-shape factor and the imaging parameter .

Fig. 4. The diagram showing the variation in the optical field diameter of the single-pass amplified laser output from amplifier.

Fig. 5. High beam quality, high-efficiency MOPA laser system.

Fig. 6. At varying pump power levels, the laser beam quality factors are assessed for single-pass amplification through the side-pump amplifier LD2, double-pass amplification with M5 positioned at location A and ordinary double-pass amplification without the 4f system.

Fig. 7. The single-pulse energy of the double-pass amplified laser, with mirror M5 positioned at location A under varying pump powers, is compared to the single-pulse energy of the ordinary double-pass amplified laser without the 4f system.

Fig. 8. At varying pump power levels, the beam quality factors for the LD2 amplified laser in single-pass configuration and for the amplified laser with M5 placed in positions A, B and C in double-pass configuration.

Fig. 9. Under a pump power of 60.7 W, when the mirror M5 is positioned at locations A, B and C, the laser undergoes double-pass amplification through the side-pumped amplifier LD2. The distribution of the optical field shape is measured at distances of 25 and 120 cm from the output aperture.

Fig. 10. When M5 is positioned at A, B and C, the amplified laser reflected by M5 reaches the focal points at SF (positions 3, 1 and 2, respectively).

Fig. 11. When the laser undergoes single-pass and double-pass amplification through the side-pumped amplifier LD2: (a) the relationship between the pump power and amplified laser energy; (b) the relationship between the pump power and optical-to-optical conversion efficiency.