High-Energy, High-Average-Power 1-Khz Burst-Mode Picosecond Laser System

We report a high-energy, high-average power burst-mode picosecond laser system, which is designed for space debris laser ranging. Pulses from a Nd : YVO4 mode-locked oscillator are first stretched by a piece of volume Bragg gratings (VBG) and then pass through an improved Michelson interferometer splitting system to obtain burst-mode pulses, which the relative amplitude and time-delay interval of each 4-pulse in bursts can be adjusted and controlled. A regenerative amplifier (RA), as a pre-amplifier, is adopted to decrease the repetition frequency of the seed beam from 80MHz to 1 KHz and raises the energy to millijoule-level. In order to reduce the performance requirement of the damage threshold of subsequent optical components and maximize the extraction of pulse energy, the Gaussian output beam of the RA is converted into a ring shaped pattern beam using an aspheric lenses reshaping system with the conversion efficiency of 93%. After a two-stage master oscillator power amplifier with 4f imaging systems, the pulse envelope energy is up to 100 mJ with the pulse duration of similar to 100 ps. To obtain high power green light, we compared the conversion efficiency of three crystals. When the fundamental frequency power is 80W, the second harmonic conversion efficiency of the first crystal (LBO, 6x6x10, theta=90 degrees, Phi=11.4 degrees) is only about 50%, as well as the second (GTR-KTP, 7x7x7, theta=90 degrees, Phi=23.5 degrees). But the conversion efficiency of the last crystal (LBO, 6x6x15, theta=90 degrees, Phi=0 degrees), reaches 68% and the output power of 532 nm as high as 50 W is obtained.