Development of an eye-safe solid-state tunable laser transmitter around 1.45 my m based on Cr 4+:YAG crystal for lidar applications

摘要

A gain switched tunable Cr4+:YAG laser was developed using a Q-switched flashlamp?pumped Nd:YAG pump laser at 10 Hz. A vacuum spatial filter (VSF) was designed in order to filter the ?hot spots? of the pump beam profile. As a result of applying the VSF, a nearly Gaussian-shaped beam profile was achieved which enabled safe pumping of the Cr4+:YAG crystal with pulse energies in excess of 100 mJ. An extensive experimental optimization of the efficiency of the wavelength converter was performed. A maximum output energy of ~7 mJ at 1430?1450 nm, corresponding to ~7% conversion efficiency (with regard to absorbed pump energy), and a pulse duration of 30?35 ns were obtained with a 25-cm-long stable resonator. Tunability in the range 1350?1500 nm and spectral linewidth of ~200G Hz were demonstrated using a 3-plate birefringent filter. The laser was multimode with a flat-top profile and sufficiently good M2~4.The performance and size of the laser are acceptable for use in a laboratory based non-scanning lidar system if a narrow-band birefringent filter is installed. In order to employ a scanning mobile lidar, high pulse frequency (>100 Hz) of the pump laser for the Cr4+:YAG laser is required. The tunability permits the improvement of the laser transmitter for water-vapor DIAL measurements at on-line wavelengths of approximately 1459 nm or 1484 nm if injection-seeding is applied.