Laser diode (LD)-pumped neodymium-doped yttrium aluminum garnet (Nd∶YAG) Q-switched laser has the advantages of small volume, lightweight, long service life, and high conversion efficiency. It is widely used in material processing, lidar, and laser ranging. Recently, the development of laser technology has necessitated an increase in the efficiency and output energy of Nd∶YAG Q-switched laser. Presently, the output optical-to-optical conversion efficiency of LD-pumped Nd∶YAG electro-optical Q-switched laser has been maintained at ~20%. Improving the optical-to-optical conversion efficiency of the laser can effectively reduce the volume and weight of the laser under the same energy output conditions. Various approaches to improve the optical-to-optical conversion efficiency have been reported. One way is to enhance the pump energy absorption. Another way is to reduce energy loss by suppressing amplified spontaneous emission (ASE) and parasitic oscillation to enhance the output optical-to-optical conversion efficiency of Q-switched laser. In this study, we propose a high-efficiency LD corner-side-pumped Nd∶YAG electro-optical Q-switched laser using a composite slab laser crystal. By improving the pump light absorption efficiency and suppressing ASE, we improve the output optical-to-optical conversion efficiency of the Nd∶YAG electro-optical Q-switched laser. We hope that our research can be helpful in improving the output energy and efficiency of Q-switched solid-state lasers.

This study is based on a composite slab laser crystal. First, the gain medium is a Nd∶YAG crystal with atomic fraction of 0.1% and cross section size of 4 mm×4 mm. Four pieces of Sm: YAG crystals with atomic fraction of 3% and thickness of 1 mm are thermally bonded around the side surfaces of the Nd∶YAG crystal to inhibit ASE and parasitic oscillation. Next, undoped YAG bulk crystals are sequentially bonded to the Sm: YAG crystal. Then, we determin the size of the composite slab laser crystal. Note that using an improved corner-side hybrid pump structure achieves a high absorption efficiency for the pump light by crossing through the active media Nd∶YAG 13 times. Next, from the ray-tracing method, we analyse the absorption efficiency and pump uniformity of the pump light using the non-sequential mode of ZEMAX simulation software. The electro-optical Q-switched system is used to study the output of the Q-switching experiment. Furthermore, the variation between free output and Q-switched output energy versus input current is studied. The optical-to-optical conversion efficiency of Q-switched output at different input currents and the dynamic-to-static ratio at the highest output efficiency are calculated. Finally, the pulse width, beam quality, and far-field spot of the laser are measured.

The free-running and Q-switched pulse outputs of the laser are measured when the pump pulse width is 230 μs and the repetition rate is 5 Hz. When the pump current is 180 A, the laser operates freely and obtains the maximum output single pulse energy of 124 mJ. With the increase in pump current, the output optical-to-optical conversion efficiency of the Q-switched pulse laser increases and then decreases. At the pump current of 170 A, we obtain the highest optical-to-optical efficiency which is 30.1%. Furthermore, the dynamic-to-static ratio is as high as 94.64% (Fig. 4). We detect the Q-switched pulse waveform using a photodetector at an output energy of 106 mJ and the detected pulse width is 15 ns [Fig. 5 (a)]. Additionally, we use a wedge prism to sample the output laser beam with repetition rate of 5 Hz and a single pulse energy of 106 mJ, and the output beam is focused by a lens with a focal length of 150 mm. Also, a charge-coupled device beam analyzer is used to measure the beam quality factor. After the measurement, the beam quality factors of Mx2=4.43 and My2=4.79 are obtained [Fig. 5 (b)].

In this paper, we investigate and experimentally design an LD corner-side-pumped Nd∶YAG electro-optical Q-switched laser, and we realize a high-efficiency 1064 nm pulse laser output. The use of a novel corner-side hybrid pump structure gives high absorption efficiency of pump light. Furthermore, four pieces of Sm: YAG crystals are bounded around the active medium Nd∶YAG to suppress parasitic oscillation and effectively reduce ASE. Finally, we obtain a single pulse energy of 106 mJ and pulse width of 15 ns in the Q-switching mode under conditions of a pulse repetition rate of 5 Hz and a pump width of 230 μs. Also, the optical-to-optical conversion efficiency is 30.1% and the dynamic-to-static ratio is 94.64%. The experimental results show that the composite slab laser crystal structure realizes high-efficiency absorption of pump light and effectively suppresses ASE and parasitic oscillation. Thus, our proposed method provides an effective method for high-efficiency 1064 nm Q-switched pulse laser output.