By using both electric-optic (EO) modulator and GaAs saturable absorber, a doubly actively-passively Q-switched laser is realized for the first time. Especially, the more symmetric and shorter pulse is generated in comparison to purely EOactively or GaAs-passively Q-switched laser. In addition, a symmetric factor is defined to describe the temporal symmetry of the pulses. The experimental results show that it is possible to obtain a more symmetric pulse in doubly Q-switched laser. The symmetry factor Pulse symmetric factor versus the transmission of output coupler

We demonstrate a continuous-wave single-frequency diamond Raman laser operating at 1178 nm by using a linear resonator that is stabilized using an intracavity [Formula: see text] element. Optimization of the single-frequency power was realized by tuning the phase matching in the [Formula: see text] element away from the second-harmonic peak to suppress neighboring modes via sum frequency generation but avoid large losses to the intracavity primary Stokes mode. A maximum single-longitudinal-mode power of 20 W at 1178 nm with an instrument-limited linewidth of 67 MHz was obtained using a 12 GHz multi-longitudinal-mode Yb-doped fiber pump laser at 1018 nm with power of 82 W. This work provides an interesting route for producing single-frequency high-power lasers near 1.2  μm utilizing diamond Raman conversion combined with broadband, high-power, low-cost YDF lasers.

We report an investigation into secondary mode suppression in single longitudinal mode (SLM) 1240 nm diamond Raman lasers. For a three-mirror V-shape standing-wave cavity incorporating an intra-cavity LBO crystal to suppress secondary modes, we achieved stable SLM output with a maximum output power of 11.7 W and a slope efficiency 34.9%. We quantify the level of χ(2) coupling necessary to suppress secondary modes including those generated by stimulated Brillouin scattering (SBS). It is found that SBS-generated modes often coincide with higher-order spatial modes in the beam profile and can be suppressed using an intracavity aperture. Using numerical calculations, it is shown that the probability for such higher-order spatial modes is higher for an apertureless V-cavity than in two-mirror cavities due its contrasting longitudinal mode-structure.

Based on a specially designed optical structure, an efficient cascaded third-harmonic-generation (THG) output of a 1064-nm, pico-seconds pulse laser is successively realized by using an NH 4 H 2 PO 4 (ADP) crystal that acts as the secondharmonic-generation component and sum-frequency-generation component. The maximum THG output is 1.61 mJ, and the highest conversion efficiency from 1064 nm to 355 nm reaches 35%, which are obviously superior to the results obtained using a KDP crystal under the same circumstance. The further phase-matching analysis indicates that this THG configuration of ADP crystal can be applied to various fundamental wavelengths in a range of 1 µm-1.1 µm. Compared with the previously reported KDP THG converter, which is based on a similar principle, the present ADP THG converter is favorable for large-energy, high-efficiency operation because of the larger effective nonlinear optical coefficient d eff and higher laser damage threshold.

We demonstrate a high-efficiency continuous-wave (CW) diamond Raman laser operating at 1178 nm with enhanced stability by using a V-cavity design. A maximum Stokes power of 39 W with a conversion efficiency of 45% was achieved using a linearly-polarized 1018 nm Yb-doped fiber pump laser. The Stokes CW power stability showed superior stability over a linear cavity when characterized over periods up to 15 min. The Stokes output was found to switch between linear, elliptical, and random polarization with varying pump polarization. The results represent a major step towards stable, efficient and high-power CW lasers at 1178 nm and at wavelengths outside the main Yb, and Nd emission bands.