We demonstrated a 50 mJ, 100 Hz, 355 nm UV laser. The third harmonic generated in a diode-pumped 200 mJ, 500 ps Nd:YAG laser system centered at 1064 nm, which based on a master oscillator power amplifier configuration. The pulse duration and temporal shape from oscillator could be modulated by an Arbitrary-Waveform-Generator and an amplitude modulator. Two LBO nonlinear crystals were employed to second and third harmonic generation respectively. The UV laser system featured an approximately flat-top temporal distribution and a 2.5% energy stability (RMS) within 1 hour.
We reported an active multipass stretcher which can deliver chirped pulse with high energy, adjustable duration and high beam quality. The stretcher system is based on a Martinez stretcher and a regenerative amplifier. The stretched pulse duration can be adjusted without changing the layout. With 1 ns stretched pulse output per roundtrip, chirped pulse with more than 10 ns can be obtained after several round-trips. A laser amplifier is introduced into the cavity to compensate the energy loss caused by the diffraction efficiency of gratings, and several millijoules pulse energy can be obtained after stretching and amplification. Benefit with the advantage of the regenerative structure, the stretched pulses have an excellent beam quality with M2 of 1.1. This novel stretcher is significant for high peak power laser systems.
To compensate for the gain saturation effect in the high-energy laser amplifier, a modified polarization beam combination (PBC) method is introduced to reshape temporal waveform of the injected laser pulse to obtain a controlled high-energy laser pulse shape after amplification. One linearly polarized beam is divided into two orthogonal polarized beams, which spatially recombine together collinearly after propagating different optical paths with relative time delay in PBC structure. The obtained beam with polarization direction being rotated by the following half wave plate is divided and combined again to reform a new beam in another modified polarization beam structure. The reformed beam is injected into three cascaded laser amplifiers. The amplified pulse shape can be controlled by the incident pulse shape and amplifier gain, which is agreeable to the simulation by the Frank–Nodvik equations. Based on the simple method, the various temporal waveform of output pulse with tunable 7 to 20 ns pulse duration can be obtained without interferometric fringes.
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