Extra-cavity radiofrequency modulator for a lidar radar designed for underwater target detection

摘要

The hybrid lidar-radar technique is commonly used for shallow underwater target detection. This technique requires a powerful blue-green RF-modulated laser with stable microwave frequency. In this paper, a novel modulator design perfectly suited for this application is proposed. It consists of an extra-cavity modulator composed of two plane mirrors and a second-harmonic generator stage within the cavity to maximize the energy efficiency. This modulator is coupled with a picosecond Nd:YAG infrared laser source to insure the emission of a powerful pulse (up to 5 mJ). Results considering this architecture show stable modulation frequency and a powerful modulated beam. As the emitted signal lasts only a few nanoseconds, a range-gating method can be used for target localization. This emitted signal has experimentally proven to preserve input beam polarization, which also can be employed to enhance the target return. (C) 2017 Optical Society of America