High peak power and high repetition rate nanosecond lasers are widely applicable and exhibit high market prospect in laser welding, laser cutting, laser cleaning, and other fields owing to their high peak power and low processing thermal effect, which can effectively solve the issues related to the precision and mechanical properties of conventional processing methods. Under high-average-power pumping, a thermal lens effect is generated, as the pump light is tightly concentrated on the laser gain medium. The processing method and quality are limited by the peak power and beam quality. To improve the peak power and beam quality of the laser, a pump-coupling structure with an adjustable pump angle and a hybrid cooling-slab module realized via a new welding process were designed in this study. A slab laser amplifier based on an angle gating structure is proposed, which offers the advantages of high peak power, high beam quality, and high conversion efficiency.

In this study, a high peak power and high repetition rate nanosecond-laser slab amplifier was investigated theoretically and experimentally. The hybrid cooling module was designed, and a new type of fusion welding technology was adopted, which effectively reduces the thermal lens effect and thermal distortion in the thickness direction of the slab crystal, realizes uniform heat dissipation, and improves the laser output power. To achieve a high power output, through efficient image transmission and by adopting aperture-filtering technology, we effectively corrected the optical aberration and reduced the free transmission of the beam, thereby improving the spot uniformity and maintaining a high beam quality. Additionally, an L-shaped optical-path pump-coupling structure with an adjustable pump light angle was designed. By designing an aspheric mirror and a trapezoidal waveguide, the pump light is uniformly pumped onto the large surface of the slab crystal, which effectively improves the pump coupling efficiency. The design of an adjustable 45° reflector frame can realize an adjustable pitch swing. This optimizes the angle and position of the pump light entering the crystal through the 45° reflector, thereby improving the beam quality. More importantly, the L-shaped optical-path pump-coupling design fully leverages the longitudinal space of the system and effectively compresses the transverse distance via the L-shaped optical-path layout, which features a short optical path, a small occupied space, and easy integration of the laser.

In this study, a nanosecond-laser slab-amplifier device with a high peak power and high repetition rate was designed. The device primarily comprises a seed source, shaping system, and slab amplifier (Fig. 5). When the pump power is 15950 W, the amplifier output power reaches 4580 W, and the change is less than ±1% within 480 min. The laser amplifier exhibits high power stability. Because the theoretical simulation does not consider the thermal effect of the laser, both the theoretical output power and growth rate are high. When the pump power is less than 11000 W, the experimental results agree well with the theoretical values, and the thermal effect is insignificant. When the pump power exceeds 11000 W, the thermal effect is improved significantly, thus resulting in an increase in the difference between the experimental and theoretical values, and the experimental output power decelerates. However, as the pump power increases, the output power does not saturate, and its center wavelength is 1064.5 nm (Fig. 7). The repetition rate of the laser is 20 kHz, the pulse width is 66.7 ns (Fig. 8), and the output pulse of the slab laser amplifier is stable without frequency drifts. The inconsistency of the pulse intensity is primarily attributed to the stability of the laser diode (LD)pump power and the thermal deformation inside the slab. Additionally, the far-field beam-intensity distribution of the laser was tested (Fig. 9). The pulse laser approximates a Gaussian beam, and the beam parameter product (BPP) is calculated to be 10 mm·mrad.

In this study, a nanosecond-laser slab amplifier with a high peak power and high repetition rate was designed. By adopting a hybrid-cooling module achieved via a new welding process and an L-shaped pump coupling structure with an adjustable pump light angle, the temperature gradient inside the crystal is effectively reduced, thereby suppressing the thermal lens effect. Additionally, the designed amplifier facilitates the integration and miniaturization of subsequent equipment. The amplifier was constructed based on the angle gating structure, and its energy-extraction efficiency was improved by establishing a three-way amplification rate equation to simulate the output characteristics. Meanwhile, the optical aberration was optimized by combining high-efficiency image transmission and aperture-filtering technology, thereby enhancing the spot uniformity. Finally, the average output power of the amplifier is 4580 W, the peak power is 3.4 MW, the pulse width is 66.7 ns, the optical-to-optical conversion efficiency is 28.7%, and the BPP is 10 mm·mrad. The amplifier exhibits application potential in steel-plate cleaning. We shall further optimize the welding technology and cooling structure, reduce the thermal effect, and improve the pump coupling efficiency to achieve higher power levels for the nanosecond-pulse laser output. Based on the requirements of different application scenarios, the pump power and shaping system can be used to adjust the power density to satisfy the application requirements of different scenarios. Additionally, the high-power pulsed laser can be extended through fiber coupling to expand its application in laser cutting and the steel-plate laser cleaning of ships.