A widely tunable 4.16–7.31 μm high-resolution mid-infrared optical parametric oscillator with a type-I BaGa₄Se₇ (BGSe) crystal pumped by a 1064 nm laser was demonstrated for the first time. We have achieved a wavelength tuning accuracy of less than 5 nm through simultaneously performing temperature tuning and angular tuning on the BGSe (46°, 0°) Optical Parametric Oscillation (OPO). The wavelength resolution will be less than 1 nm when using commercial temperature control equipment.

A temperature-sensing scheme is realized by a passively mode-locked Yb-doped fiber laser based on the nonlinear optical loop mirror (NOLM). The ambient temperature can be measured by detecting the pulse repetition frequency of the mode-locked fiber laser by an oscilloscope. When the ambient temperature increases from −40 °C to 6 °C, the pulse repetition frequency decreases linearly with a temperature sensitivity of 72.548 Hz/°C. The experimental results prove the feasibility of the mode-locked laser sensor operating in a low-temperature environment.

A high-efficiency extra-cavity Raman generator is demonstrated using a potassium yttrium tungstate (KYW) crystal for the first time, achieving switchable yellow-green laser output at 556 nm and 560 nm. The KYW Raman crystal is single-pass pumped by 532 nm green light, which is obtained by the second-harmonic generation of a 1064 nm flash-lamp-pumped Nd:YAG electro-optic (EO) Q-switched laser. When the incident pump energy at 1064 nm is 156 mJ under a repetition rate of 1 Hz, the maximum output energy reaches 51.3 mJ at 532 nm with a slope efficiency of 41.5%. By adjusting the polarization direction of the 532 nm light, two characteristic Raman shifts of the KYW crystal can be selectively excited at 765 cm⁻¹ and 905 cm⁻¹. Furthermore, the 556 nm and 560 nm visible lasers are generated with the maximum output energies of 11.6 mJ and 16.2 mJ, corresponding to the slope efficiencies of 37.6% and 48.2%, respectively. Compared with the 532 nm pulse width (18.2 ns), an obvious Raman pulse width compression effect occurred (8.2 ns).

Existing long-wave infrared (LWIR) BaGa₄Se₇ optical parametric oscillators (BGSe-OPOs) adopt linear-cavity configurations yet struggle to balance high beam quality and high output energy. To overcome this limitation, we report a compact Type I phase-matched ring cavity BGSe-OPO pumped by a 1.06 μm laser. Operating at 8.5 μm, the OPO generates 1.2 mJ single pulses with a peak power of 0.25 MW and an optical-to-optical conversion efficiency of 2%. The estimated beam quality factor M² is 9, representing a threefold enhancement relative to linear-cavity under identical pump conditions. The system features a compact footprint of 400 × 200 mm² and a far-field divergence angle of 4 mrad after 6× beam expansion, enabling practical applications in far-field monitoring.