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Cherenkov-type monochromatic terahertz (THz) generation via difference frequency generation in a general asymmetric sandwich-like waveguide is investigated theoretically. An efficient geometry-conversion from a transverse electric (TE) pump mode to a TE THz mode is mainly considered. The general expression for a Cherenkov THz field is obtained by solving the nonlinear wave equation analytically. Numerical simulation is performed on specific devices with three typical substrate materials: 1) nondoped LiNbO3; 2) BK7 glass; and 3) quartz. Characteristics of this type of THz source and parametric dependence of conversion efficiency are discussed. It is predicted that the conversion efficiency would be increased by one order by optimizing the waveguide structure.

We report an efficient continuous-wave (CW) yellow beam based on a Nd:YVO4 laser with a dual-wavelength wave plate, which is a full-wave plate at 1342 nm and a quarter-wave plate at 1064 nm. By inserting the dual-wavelength wave plate into the laser cavity and tuning the fast axis angle, based on the polarized property emission of Nd:YVO4, two simultaneous wavelengths of 1064 nm and 1342 nm were achieved. A LiB3O5 (LBO) crystal that is cut for critical type I phase matching at room temperature is used for summing frequency generation (SFG) of the laser. At an incident pump power of 5 W, a maximum CW output of 224 mW was obtained for a yellow laser with a wavelength of 593.5 nm and an optical-to-optical efficiency of 4.48%. To the best of our knowledge, this is the first time that a dual-wavelength wave plate has been used to realize a Nd:YVO4 yellow laser output.

We report herein a continuous-wave mid-infrared intra-cavity singly resonant optical parametric oscillator (ICSRO) which is the first example of ICSRO that utilize in-band pumped Nd-doped vanadate laser as pump source. A 1064 nm Nd:YVO₄ laser in-band pumped by 880 nm LD and a periodically poled lithium niobate (PPLN) crystal are employed as the parent pump laser and the nonlinear medium, respectively. The idler output wavelength tuning range is 3.66-4.22 µm. A maximum output power of 1.54 W at 3.66 µm is obtained at absorbed pump power of 21.9 W, with corresponding optical efficiency being 7.0%. The control experiment of ICSRO under 808 nm traditional pumping is also carried out. The results show that in-band pumped ICSRO has better performance in terms of threshold, power scaling, efficiency and power stability than ICSRO traditionally pumped at 808 nm.

To overcome the main drawback of poor pump absorption of Nd : YVO4 lasers in-band pumped at 914 nm, three possible methods of higher temperature, longer crystal length and higher doping concentration were experimentally studied. A Nd : YVO4 laser operating at 914 nm was used as high beam quality, narrow line-width pump source to make the measurement of pump absorption accurate. Four different Nd : YVO4 crystals were used as gain mediums to investigate the effects of crystal parameters. We found that heating the crystal effects differently on output power and overall efficiency when crystal doping concentration changed. To improve the pump absorption and meanwhile achieve high efficiency, longer crystal with proper doping concentration and pump feedback should be adopted instead of highly doped crystal.

We report a widely tunable, narrow linewidth, pulsed Ti:sapphire laser pumped by an all-solid-state Q-switched intra-cavity frequency-doubled Nd:YAG laser. By using four dense flint glass prisms as intra-cavity dispersive elements, the output wavelength can be continuously tuned over 675–970 nm and the spectral linewidth is shortened to 0.5nm. The maximum output power of 6.65 W at 780nm is obtained under 23.4 W pump power with repetition rate of 5.5kHz; corresponding to an conversion efficiency of 28.4%. Due to the gain-switching characteristics of the Ti:sapphire laser, the output pulse duration is as short as 17.6 ns.

This work demonstrates a tunable continuous-wave (CW) all-solid-state orange-red source based on sum-frequency generation (SFG), using a tunable 1.4?1.5??m signal and a 1064?nm pump of an intra-cavity periodically poled LiNbO3 optical parametric oscillator in a BBO (?-BaB2O4) crystal. Elaborate intra-cavity design ensured efficient CW singly resonant optical parametric oscillator (SRO) operation. Intra-cavity SFG made full use of the high circulating pump and signal power of the SRO under an external laser diode (LD) pump power that was ten times higher than the SRO threshold. The output wavelength tuning range was 605?623?nm. The maximum output power was 370?mW at 622.8?nm with 17.1?W LD pump power, corresponding to an overall conversion efficiency of 2.2%.

A high-efficiency 1342 nm Nd:YVO4 laser in-band pumped at 914 nm is demonstrated for the first time. Using an all-solid-state Nd:YVO4 laser operating at 914 nm as pump source, 0.86 W output was obtained with 1.82 W absorbed pump power. Corresponding slope efficiency of 65.4% was the highest of Nd:YVO4 lasers operating at 1342 nm to the best of our knowledge. Effects of crystal's doping concentration and temperature on laser power and conversion efficiency were also investigated.