A 3.6–3.9 μm Mid-IR OPO with low pulse-to-pulse fluctuation pumped by a 1064 nm pulsed laser based on pre-biased transverse voltage-boosted EO Q-switching and BC filtering

Abstract

A high peak power optical parametric oscillator (OPO) with low pulse-to-pulse fluctuation and wavelength tunable in the 3.6–3.9 μm mid-infrared (mid-IR) range was developed. OPO employed a MgO-doped periodically poled LiTaO₃ (MgO: PPLT) crystal with a poling period of 28.6 μm as a nonlinear crystal and used a 1064 nm all-solid-state pulsed laser as the laser pump source. The laser pump source used side-pumping of an Nd: YAG crystal rod by an 808 nm pulsed laser diode (LD), pre-biased transverse voltage-boosted electro-optic (PB-TBEO) Q‑switching by using an MgO-doped LiNbO₃ (MgO: LN) electro-optic crystal, and birefringent crystal (BC) filtering (hereafter referred to as the 1064 nm PB-TBEOQ‑F laser). By gradually increasing the temperature of an MgO: PPLT crystal from 40 to 200 °C, the idler light was continuously tuned across the 3908.9 nm–3642.3 nm range. In pulse repetition frequency range of 100 Hz to 1.0 kHz, both the 1064 nm PB-TBEOQ‑F laser and the pulsed idler light output from the OPO maintained high peak power and short pulse duration, exhibiting low pulse-to-pulse fluctuations in single-pulse energy and pulse duration. For the first time, a 1064 nm pulsed laser based on pre-biased transverse voltage-boosted EO Q‑switching and BC filtering was employed as the pump source to realize a 3764.1 nm pulsed idler at an optimal tuning temperature of 150 °C. At an LD pump current of 100 A and a pulse repetition rate of 100 Hz, the pulse duration and single-pulse energy of the pulsed idler light at 3764.1 nm were measured to be 5.27 ns and 8.061 mJ, respectively. The system showed excellent stability with pulse-to-pulse fluctuations of only ± 0.35% in single-pulse energy and ± 0.92% in pulse duration.