Megawatt peak power, repetition rate tunable, high beam quality nanosecond QCW-LD end-pumped Nd:YVO₄ MOPA system

A megawatt (MW) peak power, tunable repetition rate nanosecond (ns) laser system based on a quasi-continuous wave (QCW) laser diode (LD) end-pumped master oscillator power amplifier (MOPA) structure was demonstrated. A 1064 nm electro-optically Q-switched Nd:YVO₄ laser was used as the seed source, generating a pulse duration of 4.6 ns, a single pulse energy of 530 μJ, a repetition rate of 1 kHz, and beam quality factors of <b><i>M_x</i></b>² = 1.38 and <b><i>M_y</i></b>² = 1.20. After the two-stage QCW end-pumped Nd:YVO₄ amplifier, the single pulse energy was boosted to 16.58 mJ, the pulse duration was shortened to 3.5 ns with a peak power of 4.73 MW, and the beam quality was improved to <b><i>M</i></b>²≤1.12. The repetition rate was adjustable by using an electro-optic pulse picker while maintaining the repetition rate of the seed laser unchanged, and thus was beneficial for improving the reliability of the output pulsed laser. Furthermore, the gain of QCW end-pumped amplifiers was theoretically estimated using a modified Frantz-Nodvik equation model, the theoretical results were great well with the experimental results.