A laser amplifier can shape the sub-ns pulses of a microchip laser (Opt. Express 26(07), 8609 (2018) and 27(14), 19555 (2019)). In this work, by numerical calculations based on the rate equation for population inversion and photon density taking into account temporal pulse shape, we simulated propagation in the highly excited Nd:YAG-rod amplifier of sub-ns Micro-MOPA and proved amplification conditions to compress the pulse length toward under 100 ps operation.
>2 PW/sr-cm2 highly brightness Micro-MOPA was achieved. This Micro-MOPA can generate 100 mJ-class and PW/sr-cm2-class pulse with the A3 paper size footprint.100 Hz operation of the Micro-MOPA with over 2 PW/sr/cm2 was achieved. Micro-MOPA system can generate 100 mJ-class and PW/sr/cm2-class pulse with paper size footprint. However, previous repetition rate is limited to 10 Hz in spite of the oscillator and the amplifier design for 100Hz operation due to its thermal problem. However, current repetition rate is limited to 10 Hz in spite of the oscillator and amplifier design for 100Hz operation, because tThe laser diode side-pumped Nd:YAG rod of the amplifier for Micro-MOPA causes lens effect in high brightness beam operation and the focused beam from the rod causes damage to optics. We measured the thermal lens effect of the amplifier Nd:YAG rod to optimize the design of 100 Hz and PW/sr-cm2 class Micro-MOPA. Measured thermal lens focal length at 100 Hz is 0.5 m, and we found thermal lens have no significant time dependence in spite of its QCW pumping. From this result, we insert the optics with composite focal length of 0.45 m to cancel thermal focusing. On the other hand, such the optics is designed on the assumption of thermal lensing, therefore, we have to align optics with pumped amplifier. However, unaligned pumped beam already has 100mJ class energy and it is easy to break optics. To keep thermal lensing constant and to avoid this difficulty, we focused that thermal lensing have no significant time dependence and propose procedure for alignment and amplified energy control by using pumping delay timing shift between oscillator and amplifiere. From these improvements, we have demonstrated the 100 Hz operation of the Micro-MOPA with over 2 PW/sr-cm2.