2. The pulse width of electro-optical Q-switched lasers

Electro-optical Q-switching is a kind of fast switching technology, and its fast response speed enables it to obtain narrow pulse width laser output. According to the EO Q-switching theory of ZAYHOWSKI J J et al., the cavity length and repetition frequency will affect the pulse width of the laser. That’s to say, narrow pulse width laser output can be obtained by compressing the cavity length or reducing the repetition frequency. In order to obtain the narrow pulse output under the condition of high repetition frequency, the cavity dumping technology which is independent of the repetition frequency can be used. In the following, the development of EO Q-switched lasers with high repetition frequency and narrow pulse width is reviewed from three aspects: the fast switching capability of the Q-switch, the short-cavity method and the EO cavity dumping technology.

2.1 Fast EO Q-switching

EO Q-switch can quickly switch between very large and very small resonator losses, and complete a switching action within 10^-8 seconds. It is an effective method to generate lasers with narrow pulse widths of nanoseconds. It is easy to obtain stable pulse output shorter than 10 ns. In 2010, researchers used LD end-pumped Nd:YVO₄ (www.wisoptic.com) crystal and LGS Pockels cell to design an efficient and stable resonator, and obtained laser output with repetition frequency of 30 kHz and pulse width of 9.1 ns. In 2019, by using LD end-pumped Nd:YVO₄ crystal and RTP crystal pair as the EO Q-switching device to reduce the thermal effect and apply mode-matching technology, a stale high frequency output was obtained with pulse width of 9 ns, while the repetition frequency was su200 kHz. In 2020, people used LD to pump Nd:YVO₄ crystal, and apply an optimal voltage to drive the Pockels cell, therefore obtain a narrow pulse width laser output with repetition frequency of 1 kHz and pulse width of 0.77 ns.