Photon-counting light detection and ranging (LiDAR) based on single-photon detection technology offers the advantages of high detection-signal integrity, high time resolution, high measurement accuracy, and high sensitivity, and is widely used in long-distance ranging and imaging fields. Compared with the conventional linear photoelectric detection technology, single-photon detection technology requires lower energy from the laser. However, it imposes new requirements for the laser: repetition frequencies in the kilohertz range to ensure sufficient sampling frequency, pulse widths in the nanosecond to ensure detection accuracy, high beam quality to ensure detection stability and sensitivity, low weight, and small volume. This paper focuses on the application of single-photon detection technology in LiDAR and reports a 532-nm solid-state laser with a high repetition frequency and narrow pulse width. The laser is miniature and lightweight, which can satisfy the application requirements of spaceborne photon-counting LiDAR for space light sources.

To achieve a miniaturized and lightweight laser, six single-tube 808-nm chip on submount (COS) semiconductor lasers were used as the pump source. Using an incoherent space-beam combining system that combines a step-distributed heat sink with a polarization beam combining system, a highly integrated six single-tube pump coupling system was constructed to obtain a miniaturized and high-brightness pump source. COS packaging technology offers the advantages of high integration and reliability, which can integrate the pump laser diode (LD) with the laser path structure to achieve laser integration. By selecting Nd∶YAG as the gain medium and Cr∶YAG as the passive Q-switched crystal, the gain medium and passive Q-switched crystal were bonded to achieve an integrated resonator, which can not only miniaturize the laser structure but also form a short-cavity structure to achieve a narrow-pulse-width output. The pumped LD output laser was collimated by the fast- and slow-axis collimator and then focused in the laser gain medium through the focusing mirror. Finally, potassium titanyl phosphate (KTP) crystal was used for external-cavity frequency doubling to output a 532-nm green light.

When the operating current of the LD is 6 A, the output power of the pump light is 4.4 W, the laser output repetition frequency is 1 kHz, and the single-pulse energies are 0.42 mJ and 0.24 mJ at wavelengths of 1064 nm and 532 nm, respectively. The frequency doubling efficiency is 57.1%. The obtained pulse waveforms are shown in Fig, 5, which shows a fundamental laser-beam pulse width of 1.25 ns and a frequency-doubled laser-beam pulse width of 1.17 ns. The beam qualities of the output laser are Mx2=1.43andMy2=1.46, as shown in Fig. 9. The size of the laser is 116 mm (length)×57 mm (width)×22 mm (height), and its mass is 386.7 g, as shown in Fig. 10.

Herein, a miniaturized and lightweight high-repetition-frequency narrow pulse width solid-state laser suitable for space exploration is introduced. YAG/Nd∶YAG/Cr∶YAG bonded crystal was pumped using multiple single-emitter diode lasers, and KTP crystal was used for external-cavity frequency doubling to achieve a 532 nm laser output with a single-pulse energy of 0.24 mJ and a pulse width of 1.17 ns at repetition frequency of 1 kHz. The beam quality factors areMx2=1.43andMy2=1.46. The laser head measures 116 mm (length)×57 mm (width)×22 mm (height) and weighs 386.7 g, thus achieving the development goals of miniaturization and lightweightness, and can be used as the space light source for spaceborne photon-counting LiDARs.