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A low-order wavefront aberration self-compensation high power Nd:YAG slab laser module is developed and demonstrated. By numerical simulating the thermal distribution and transmission wavefront of the slab laser medium, a thermally-compensated heat removal geometry is developed to reduce the wavefront distortion. This method allows the non-uniform cooling to flatten the thermal gradient distribution in the width direction of the slab. By using the optimized gain module as an amplifier, the laser output power of 7.8 kW is achieved. Compared to the traditional module, the output power is 7.3 kW, and the peak-to-valley (PV) value of the wavefront distortion is reduced from 17.21 to $2.05~\mu \text{m}$ under full power, the beam quality factor $\beta $ is improved from 12.7 to 3.5 times diffraction limited while without additional correction system.

We report a new approach to effectively improve the optical-to-optical efficiency for quasi-continuous-wave (QCW) lasers by adjusting the pump pulse duration. During our single-slab laser test, an optical-to-optical conversion efficiency of 57% and a slope conversion of 67.8% are obtained with a maximum average output power of 7.3 kW, operating at a pulse repetition rate of 160 Hz with 470- $\mu \text{s}$ pulse duration. To the best of our knowledge, this represents the highest optical-to-optical efficiency for a QCW face-pumped Nd:YAG slab laser with such high power output ever reported.

A high-efficiency picosecond (ps) 532-nm green laser with high pulse energy and high peak power at 5-kHz repetition rate was demonstrated by second-harmonic generation (SHG) from a 1064-nm master oscillator power amplifier (MOPA). The MOPA was based on the Innoslab structure under diode directly pumping, producing 4.8-mJ, 25-ps fundamental laser at the repetition rate of 5 kHz after a three-stage Innoslab amplification system. With a pulse energy of 2.93 mJ in the fundamental and using a type I noncritically phase matched lithium triborate crystal, the pulse energy of SHG was up to 1.96 mJ per pulse with a pulse width of 18.9 ps, which corresponds to a peak power of 104 MW in the green and SH conversion efficiency as high as 67%. The SHG green beam quality factor was measured to be $M^{2} = 1.75$ .

We demonstrate an efficient high power and high brightness yellow-green 556-nm laser generated from second harmonic generation (SHG) of a master oscillator power amplifier (MOPA) laser system at 1112 nm. The oscillator was a pulsed laser diode (LD) pumped and Q-switched Nd:YAG laser at 1112 nm operated at TEM00 mode with an average output power of 35 W, providing 200-μs long macropulses and constituting 700-ns micropulses. The seed laser was amplified by two LD side-pumped Nd:YAG amplifiers and the MOPA system delivered a maximum output power of 78 W. Using a type-I phase-matching lithium triborate nonlinear crystal, the SHG maximum output power of 48 W was obtained at 556 nm with a conversion efficiency as high as 61.5%. The beam quality factor was measured to be M2 = 1.53 and the corresponding brightness was as high as 6.63 × 109 W/cm2·sr.