Zhang Xingyu

Inflection point of the spectral shifts of the random lasing in dye solution with TiO2 nanoscatterers

We report the inflection point of the spectral shift of random lasing, from blue shift to red shift, in Rhodamine 6G dye solution with TiO2 nanoscatterers under picosecond pulses pumping, on increasing the scatterer density for certain dye concentrations. The red shift, resulting from the re-absorption and re-emission of the dye, indicates a longer optical path length of the emitted laser travelling inside the media. The diffusion theory is provided to show the discrepancy in the theory and the experimental results, which show that the light stays in the medium longer than the theory predicts. So this inflection point shows that the system changes from a diffusion system to a weakly localized one. The spectral width shows similar behaviour, for a longer optical path length results in a broader spectral width.

Low Threshold and High Efficiency Nd:S-VAP Laser

The absorption spectrum of a new sort of crystal Nd:S-VAP was measured, which showed that Nd:S-VAP can be appropriately pumped at 583.0 and 809.0 nm. By using tunable dye-laser (570.0-600.0 nm) as pumping light, the performance of low threshold and high efficiency Nd:S-VAP laser has been realized. The characteristics of the output laser, such as 1.5 nm linewidth, 5 ns pulse width, almost total polarity, up to 50% conversion efficiency, down to 2 mJ threshold energy and so on, were presented. Meanwhile, the prospect of Nd:S-VAP crystal for low threshold, high efficiency miniature laser was discussed.

Modelling of passively Q-switched lasers with intracavity Raman conversion

We present a model of passively Q-switched Raman lasers by utilizing the rate equations. The intracavity fundamental photon density, Raman photon density and the initial population-inversion density of the gain medium are assumed to be of Gaussian spatial distributions. These rate equations are normalized by introducing some synthetic parameters and solved numerically, and a group of general curves are generated. From these curves we can understand the dependence of the Raman laser pulse characteristics on the parameters about the pumping, the gain medium, the Raman medium and the resonator. An illustrative calculation for a passively Q-switched Nd3+:GdVO4 self-Raman laser is presented to demonstrate the usage of the curves and related formulas.

Theory of intracavity-frequency-doubled quasi-three-level cw lasers

The rate equations for the intracavity-frequency-doubled quasi-three-level lasers are developed. By normalizing the related parameters, it is shown that the general solution to the rate equations is dependent upon four dimensionless parameters: the normalized reabsorption loss, the pump to laser-mode size ratio, the normalized pump level, and a parameter written as ηshg, which is related to the ability of the nonlinear crystal to convert the fundamental to the second harmonic. By numerically solving these rate equations, a group of general curves are obtained to express the relations between the solution and the four dimensionless parameters.

Xenon Flash Lamp Pumped Self-Frequency Doubling NYAB Q-Switched Laser

By using xenon flash lamp as pumping light source and BDN dye film as passive Q-switch or KD* P crystal as active Q-switch, we have, for the first time, realized Q-switching run from 1.06 μm to 0.53 μm in the NdxY1-xAl3(BO3)4 (NYAB) self-frequency doubling laser and obtained MW/cm2 giant pulse output at 0.53 μm wave length. Meanwhile, the green light output energy and pulse duration were measured under the conditions of different resonator lengths and pumpings. The experimental results are in agreement with the numerical solutions of the Q-switching coupling wave rate equations. Moreover, the ways of improving the green laser output peak power are proposed.

Diode-pumped Passively Q-switched Nd:YAG/BaWO4/KTP Yellow Laser

A diode-pumped passively Q-switched Nd:YAG/BaWO4/KTP yellow laser is presented for the first time. The obtained maximum average output power, conversion efficiency, pulse energy were 1.21 W, 9.06%, and 68.5 μJ, respectively.

Modeling laser-diode-pumped Tm3+-doped fiber amplifiers

A theoretical model is developed for the laser-diode-pumped Tm3+-doped fiber amplifier, and a set of ordinary differential equations (ODEs) governing the dynamics of dual-wavelength pumping scheme (1.4μ+1.56μ) based on the rate equations and propagation equations was established. The relationship between the spectra gain and pump power was described and analyzed by numerically solving the ODEs. Spectral gain as a function of longitudinal position along the fiber was given to optimize the fiber length; spectral gain per unit length, and fractional inversion were used to explain the gain shift property of TDFA. The theoretical results agree well with the experimental data.