Fig. 1. End-pumped two-segmented crystal.

Fig. 2. Cross-sectional temperature distributions of Nd:YVO₄ with (a) 0.2 + 0.5% (atomic fraction) Nd³⁺-doped and (b) 0.3% (atomic fraction) Nd³⁺-doped on the x–z plane, and (c) the comparison of the temperature rise of the cross-section center along the z axis.

Fig. 3. In the case of the beam filling factor ω_l/ω_p = 1, the values of the 5th to 15th Zernike coefficients of the probe laser beam at the rear end of the end-pumped single-segmented and two-segmented crystals are calculated, respectively.

Fig. 4. Experimental setup for measuring the phase of the probe laser beam at the rear end of the crystal.

Fig. 5. In the cases of the single-segmented and two-segmented crystals as gain media, with the beam filling factors ω_l/ω_p from 0.5 to 1, the (a) spherical aberration coefficient c₁₁ (theoretical and experimental) and (b) beam quality factor on x axis M_x² (theoretical and experimental) are calculated and measured.

Fig. 6. In the cases of the single-segmented and two-segmented crystals as gain media, with the beam filling factor ω_l/ω_p from 0.5 to 1, (a) the spherical aberration coefficient c₁₁ (theoretical) and (b) the beam quality factors on x axis M_x² (theoretical and experimental) of the amplified laser at the rear end of two crystals are calculated and measured.

Fig. 7. In the cases of the beam filling factor ω_l/ω_p from 0.5 to 1 with the single-segmented and two-segmented crystals as gain media, the output power P_out is measured experimentally, and the corresponding extraction efficiency η_extr is calculated.

Fig. 8. In Case 1 and Case 2, the (a) output power and (b) the corresponding extraction efficiency are calculated.

Fig. 9. Experimental setup of high-power end-pumped multistage amplifier system.

Fig. 10. Output power and extraction efficiency of experimental and theoretical results of the multistage amplifier system.

Fig. 11. The beam quality of x and y axes is measured in the four-stage amplifier system. (a) First-stage amplifier with P_out = 63.3 W; (b) second-stage amplifier with P_out = 132.3 W; (c) third-stage amplifier with P_out = 205.2 W; and (d) fourth-stage amplifier with P_out = 280.2 W.