High-power and widely tunable continuous-wave optical parametric oscillators (cw OPOs), as mature radiation sources in the mid-infrared range, are limited by their frequency fluctuation. We built a cw OPO working at the near- and mid-infrared ranges and discuss the extent to which its frequency stability is affected by the mechanical temperature and the air pressure of the cavity. In addition, we artificially provoked mode hops by changing the above two factors to analyze the thermal-induced refractive index variation of the crystal. An inequality between the spacing of the hops and the free spectrum range (FSR) was observed. The wavelength stability of the cw OPO was guaranteed passively, and the longest mode-hopping-free time exceeded 13 h through sealing the cavity and thermal control. Further analysis of factors affecting frequency drift is critically essential for the reliability of cw OPO, particularly in environments outside the laboratory, and may provide a new method for high-precision tuning wavelengths.

High-power optical parametric oscillators (OPOs), as mature radiation sources in mid-infrared (MIR), degenerate gradually with wavelength increase, mainly above 3700 nm. Using a periodically poled magnesium-oxide-doped lithium niobate (MgO:PPLN) as the nonlinear crystal, we build a high-power signal-resonant OPO pumped by ytterbium-doped fiber laser (YDFL). To improve the OPO’s output power at ~3.8 μm, the parameters, such as the pump beam’s waist diameter and location, the curvature radius of the output coupler and the length of MgO:PPLN, are discussed in detail. When pump power is 79 ± 4 W with a repetition rate of 200 kHz, the OPO provides up to 8 ± 0.4 W average power in beam quality with M² factors of ~1.84 and ~1.69 in the two axes. Under the highest output power, the center wavelength of the idler beam is 3768.4 nm with a full-width at half-maximum (FWHM) bandwidth of ~18.6 nm. When the output power reaches ~6.3 W, its power stability is 1.6% root mean square (RMS) over 7 h. Further analysis of the factors affecting OPO’s performance and simple structure are critically essential for compact OPO prototypes with a capacity of high output power.

This paper introduces what we believe to be the novel use of a 405 nm laser to mitigate pyroelectric-induced photorefractive effects in MgO-doped lithium niobate (MgO:LN) and MgO-doped periodically poled LN (MgO:PPLN). The pyroelectric effects inducing light-induced variations in the space charge field resulted in beam distortion when a 1064 nm laser passed through uniformly heated MgO:LN and MgO:PPLN crystals. By co-linearly irradiating the crystals with a 405 nm laser, approximately 80% of the beam distortion was eliminated, with a comparison of the effects of varying power levels. The findings highlight the efficacy of 405 nm laser-induced photocarriers in mitigating beam distortion. This methodology extends to optical parametric oscillators, enhancing operational stability post-frequency conversion by a factor of ten. This innovative approach is poised to advance the widespread application and development of LN in laser technologies and photonic devices.

Two-dimensional TiTe₂ materials have excellent optical and electrical properties due to their unique semi-metallic properties and are widely used in detectors, photocatalysis, and field effect tubes. However, their potential in field of nonlinear optics (NLO) and ultrafast photonics has not been explored. In this paper, TiTe₂ nanosheets are prepared by liquid-phase exfoliation, and their excellent nonlinear optical properties are being demonstrated. Z-scan measurements show that their nonlinear absorption coefficients are -6.83 ± 0.52 and -15.10 ± 0.82 cm GW^-1 at 1560 and 2000nm, respectively, exhibiting saturable absorption properties. Two saturable absorbers (SA) based on TiTe₂ nanosheets are prepared, one by encapsulating TiTe₂ nanosheets in a polyvinyl alcohol (PVA) film and the other by depositing them on D-shape fiber (DSF). Finally, a Q-switched operation is achieved using TiTe₂-PVA SA, with the maximum output power of 14.2 mW, corresponding to a pulse energy of up to 212.9 nJ. Stable mode-locked operation is achieved using TiTe₂-DSF SA with a signal-to-noise ratio and pulse duration of 70 dB and 788 fs, respectively. Notably, this is the first time that TiTe₂ nanosheets have been used as SA. The results suggest that TiTe₂ nanosheets are a high-performance nonlinear material that provides a new impetus for the development of NLO and ultrafast photonics.

A continuous-wave, tandem optical parametric oscillator (TOPO) based on a MgO-doped periodically poled LiNbO₃ (MgO:PPLN) is demonstrated. Because the MgO:PPLN is tandemly pumped by the OPO’s signal beam, it outputs simultaneously two groups of signal and idler with a single pump source. The entire range spans from 1398 to 1490 nm, 1914 to 2107 nm, 3720 to 4444 nm, and 4849 to 5190 nm, which is limited by periods of the MgO:PPLN and cavity mirror coatings. The TOPO, whose oscillation threshold of pump power exceeds 7 W, can be easily triggered by marginally increasing the pump power as long as the OPO process occurs. The maximum idler powers are respectively 2.6 W (at 3896 nm) and 34 mW (at 4863 nm), and the corresponding signal powers are both nearly one hundred milliwatts.

A continuous-wave, tandem optical parametric oscillator (TOPO) based on a MgO-doped periodically poled LiNbO₃ (MgO:PPLN) is demonstrated. Because the MgO:PPLN is tandemly pumped by the OPO’s signal beam, it outputs simultaneously two groups of signal and idler with a single pump source. The entire range spans from 1398 to 1490 nm, 1914 to 2107 nm, 3720 to 4444 nm, and 4849 to 5190 nm, which is limited by periods of the MgO:PPLN and cavity mirror coatings. The TOPO, whose oscillation threshold of pump power exceeds 7 W, can be easily triggered by marginally increasing the pump power as long as the OPO process occurs. The maximum idler powers are respectively 2.6 W (at 3896 nm) and 34 mW (at 4863 nm), and the corresponding signal powers are both nearly one hundred milliwatts.