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

Passive Q-switched pulse lasers equipped with high quality gain media are expected to be the preferred UHF pulse sources containing THz pulse train. Based on a Yb: LuAG passively Q-switched laser pumped by a laser diode with a Yb ratio of 15at.% in Yb: LuAG, stable quasi-single longitudinal mode laser pulse trains and quasi-double longitudinal mode oscillation unstable pulse trains were observed experimentally, and the ultra-high-frequency (UHF) pulses excited by the high power unstable pulse trains were studied. The spectrum of the pulse train includes the low frequency spectrum with the base frequency below 500 KHz and the ultra-high frequency spectrum with the base frequency above 10 4 KHz. The base frequency change law of UHF spectrum with the increase of pump power conforms to the frequency doubling frequency principle of spectrum changing to higher frequency. With the increase of pump power, the fundamental frequency increases by 2 n , reaching 0.32 THz in the experimental range of this paper. After the UHF pulse train is filtered at 1.25*10 5 KHz, a single UHF pulse train and its corresponding spectrum are obtained. The average peak power of UHF spectrum pulse increases with the increase of pump power.