| Abstract [eng] |
In the past decade, there has been intensive development of sub-nanosecond passive q-switched small cavity oscillators. By pumping short-length resonators with laser diodes, it is possible to generate energy pulses of several hundred microjoules, with a duration of less than 1 ns. Short cavity oscillators are compact, air-cooled, and produce high spatial quality beams. However, in many cases, the energy of the laser pulse is not sufficient for specific applications. The aim of this work is to develop a low repetition rate, compact, air-cooled, optical system capable of generating sub-nanosecond high-energy ≈100 mJ pulses. In this work, a theoretical modeling of a picosecond pulse amplification system is described, based on the Frantz-Nodvik optical amplification equation. Using the mentioned modeling, the amplification of both single-stage and two-stage amplification systems was simulated. In this way, the threshold optical parameters—input energy and beam diameter necessary to achieve the set goal were determined. The amplification in a two-pass Nd:YAG amplification module, pumped by VCSEL diodes, was experimentally investigated. A short resonator Nd:YAG laser was used for amplification, emitting 1064 nm pulses – 2.4 mJ, 358 ps at a repetition rate of 10 Hz. In the two-pass Nd:YAG amplification module, pumped by 3.2 kW of quasi-continuous operation power with VCSEL diodes, ≈26 fold amplification was achieved. The output pulse energy exceeded 50 mJ with a beam quality factor M2 ≈ 1.2. To achieve the set goal of >100 mJ, an additional longitudinal amplification stage was implemented. Nd:YAG crystal pumped with a 225 W diode bar resulted in maximum amplified pulse energy of ≈ 16 mJ. However, to reduce amplifier feedback and preserve the Gaussian beam distribution, the additional amplification stage was optimized with lower amplification E = 10 mJ. By implementing a two-stage amplification configuration, the pulses were amplified to 104 mJ. However, due to inhomogeneous amplification and experienced distortions, the beam profile loses its Gaussian shape. The spatial quality of the amplified beam can be improved by performing spatial filtering in a vacuum cell. |
