Instability and ultra-high frequency spectrum pulse train in passively Q-switched Yb:LuAG ceramic laser

The ultra-high-frequency pulse trains in a Yb:LuAG passively Q-switched laser with a Yb ratio of 15 at. % are experimentally investigated. The pulse trains consist of a low-frequency harmonic spectrum pulse train with a fundamental frequency below 500 KHz as the source and an ultra-high-frequency harmonic spectrum pulse train with an exciting fundamental frequency above 104 KHz. The basic frequency of the low spectrum increases approximately linearly with increasing pump power. The change law of the fundamental frequency of the ultra-high frequency spectrum with the increase in pump power conforms to the frequency-doubling principle of the harmonic spectrum changing to a higher frequency, and increases exponentially with A × 2n (n is a natural number, A = 1.25 × 108, 1.552 × 108, or 1.0 × 108 Hz). In this paper, the base frequency range of the ultra-high-frequency spectrum was 0.077 73 GHz–0.66 THz. The maximum average peak power of an ultra-high-frequency pulse was 18.25 mW, and the minimum width of an ultra-high-frequency pulse was 3.2 ps.