Wang Yuye

Low Threshold and High Conversion Efficiency Nanosecond Mid-Infrared KTA OPO

Based on a Type II non-critically phase-matched KTA crystal, a low-threshold and high conversion efficiency mid-infrared optical parametric oscillator (OPO) pumped by a diode-end-pumped Nd:YVO4 laser is demonstrated. The OPO threshold is only 0.825 W. The maximum output power of 435mW at 3.47 μm is achieved with the repetition rate of 30 kHz, corresponding to an optical-to-optical conversion efficiency of 4.4%. The photon conversion efficiency is as high as about 64%. The pulse width is 3.5 ns with a peak power of 4kW for the maximum output power.

Efficient Compound-Cavity Eye-Safe KTP OPO at 1.57 μm Pumped by an Electro-Optic Q-Switched Nd:YAG Laser

An efficient high-energy eye-safe optical parametric oscillator (OPO) based on a type-II non-critically phase-matched KTP crystal is demonstrated. The KTP OPO is pumped by a quasi-cw diode side-pumped electro-optic Q-switched Nd:YAG laser in a compound-cavity configuration. The maximum output energy of the signal wavelength at 1.57 μm is 66.5 mJ, corresponding to an electrical-to-optical conversion efficiency of 4.47% and an optical-to-optical conversion efficiency of 12.1%. The pulse width (FWHM) is about 3.6ns with a peak power of 18.5 MW. The output energy is insensitive to repetition rate and demonstrates good stability.

Numerical Modelling of QCW-Pumped Passively Q-Switched Nd:YAG Lasers with Cr4+:YAG as Saturable Absorber

Passively Q-switched quasi-continuous-wave (QCW) diode-pumped Nd:YAG laser with Cr4+:YAG as saturable absorber is numerically investigated by solving the coupled rate equations. The threshold pump rate for passively Q-switched QCW-pumped laser is derived. The effects of the pump rate and pump-pulse duration on the laser operation characteristics are studied theoretically. The pump power range can be estimated according to the number of output pulses. The numerical simulation results are in good agreement with the experimental results.

Low-loss terahertz waveguide with InAs-graphene-SiC structure

We demonstrate a low-loss terahertz waveguide based on the InAs-graphene-SiC structure. By analyzing the terahertz waveguide proposed in this paper, we can obtain that it is the characteristic of a low transmission loss coefficient (αloss ≈ 0.55 dB/m) for fundamental mode (LP01) when the incident frequency is larger than 3.0 THz. The critical radii of the inside and outside cylinders have been found for the high-quality transmission. The large inside radius and the high transmission frequency result in a flat transmission loss coefficient curve. As a strictly two-dimensional material, the double graphene surface rings perform better to improve the quality of transmission mode. These results provide a new idea for the research of the long-distance THz waveguide.

Experimental 511 W Composite Nd:YAG Ceramic Laser

We demonstrate a 511 W laser diode pumped composite Nd:YAG ceramic laser. The optical pumping system is consisted of five laser diode stacked arrays arranged in a pentagonal shape around the ceramic rod whose size is Φ6.35×144 mm. When the pumping power is 1600 W, the cw laser output up to 511 W at 1064 nm can be obtained with a linear plano–plano cavity, and the optical-to-optical efficiency is 31.9%. To our knowledge, this is the highest value of laser output by using a newly invented composite Nd:YAG ceramic rod as the gain medium.

High Energy Terahertz Parametric Oscillator Based on Surface-Emitted Configuration

We experimentally demonstrate a high power nanosecond pulsed terahertz (THz)-wave parametric oscillator (TPO) by using a wide pump beam. A surface emitted cavity configuration is employed to reduce the THz absorption in MgO:LiNbO3 crystal. The THz wave can be tuned from 1 THz to 3 THz. A maximum THz output energy of 438 nJ/pulse is achieved at 1.56 Hz using a 4.5-mm-diameter pump beam with a pulse energy of 226 mJ pump energy with the repetition of 10 Hz, corresponding to the energy conversion efficiency of 1.94 × 10−6.

A high-power high-stability Q-switched green laser with intracavity frequency doubling using a diode-pumped composite ceramic Nd:YAG laser

We successfully obtain a high-average-power high-stability Q-switched green laser based on diode-side-pumped composite ceramic Nd:YAG in a straight plano-concave cavity. The temperature distribution in composite ceramic Nd:YAG crystal is numerically analyzed and compared with that of conventional Nd:YAG crystal. By using a composite ceramic Nd:YAG rod and a type-II high gray track resistance KTP (HGTR-KTP) crystal, a green laser with an average output power of 165 W is obtained at a repetition rate of 25 kHz, with a diode-to-green optical conversion of 14.68%, and a pulse width of 162 ns. To the best of our knowledge, both the output power and optical-to-optical efficiency are the highest values for green laser systems with intracavity frequency doubling of this novel composite ceramic Nd:YAG laser to date. The power fluctuation at around 160 W is lower than 0.3% in 2.5 hours.

Intersubband absorption with difference-frequency generation in GaAs asymmetric quantum wells

An asymmetric quantum well (AQW) is designed to emit terahertz (THz) waves by using difference frequency generation (DFG) with the structure of GaAs/Al0.2Ga0.8As/Al0.5Ga0.5As. The characteristics of absorption coefficients are analysed under the parabolic and non-parabolic energy-band conditions in detail. We find that the absorption coefficients vary with the two pump optical intensities, and they reach the maxima when the pump wavelengths are given as ?p1 = 9.70 ?m and ?p2 = 10.64 ?m, respectively. Compared with non-parabolic conditions, the total absorption coefficient under parabolic conditions shows a blue shift, which is due to the increase in the energy difference between the ground and excited states. By adjusting the two pump optical intensities, the wave vector phase-matching condition inside the AQW is satisfied.

Threshold Analysis of a THz-Wave Parametric Oscillator

The parametric gain of a terahertz wave parametric oscillator (TPO) is analyzed. Meanwhile the expression of TPO threshold pump intensity is derived and theoretically analyzed with different factors. The effective interaction length between the pump wave and Stokes wave is calculated, and particular attention is paid to the coupling efficiency of the pump wave and Stokes wave. Such an analysis is useful for the experiments of TPO.

Passively Q-Switched Quasi-Continuous-Wave Diode-Pumped Intracavity Optical Parametric Oscillator at 1.57 μm

We report on a passively Q-switched quasi-cw diode-pumped Nd:YAG including an intracavity optical parametric oscillator. The dynamics of this system is described by solving the coupled equations. The effect of the initial transmission of Cr4+:YAG saturable absorber on the signal wave operation is studied. Under optimum conditions, we achieve 2.3 m J energy at 1.57μm wavelength for 40 Hz repetition rate. The peak power of the pulses amounts to 0.88MW with the pulse width of 2.6ns. When the Fresnel reflection losses of the filters are taken into account, the pulse energy would be higher than 2.3 m J. To the best of our knowledge, this is the highest pulse energy and peak power for such a type of single resonant quasi-cw diode pumped Nd:YAG/Cr4+ :YAG IOPO laser.