Guiqiu Li

A new model of laser-diode end-pumped actively Q-switched intracavity frequency doubling laser

The intracavity photon density and the initial population-inversion density are assumed to be Gaussian spatial distributions in the rate equations of a laser-diode end-pumped actively Q-switched intracavity-frequency-doubling laser. In addition, the influence of the pump rate, the thermal effect in the gain medium and the change of the photon density along the cavity axis have been taken into account. These coupled rate equations are solved numerically, and the dependences of pulse width, single-pulse energy and peak power on incident pump power are obtained for the generated-green-laser pulses. In the experiment, a laser-diode end-pumped actively Q-switched Nd:YVO/sub 4//KTP laser with acoustic-optic-modulator is realized and the experimental results agree with the numerical solutions.

Dual-loss-modulated Q-switched and mode-locked YVO 4 /Nd:YVO 4 /KTP green laser with EO and Cr 4+ :YAG saturable absorber

By simultaneously employing the electro-optic (EO) modulator and Cr(4+):YAG saturable absorber, a diode-pumped dual-loss-modulated Q-switched and mode-locked (QML) YVO(4)/NdYVO(4)/KTP green laser is presented. In comparison with the singly passively QML green laser with Cr(4+):YAG, the dual-loss-modulated QML green laser with EO and Cr(4+):YAG can generate more stable pulse train with deeper modulation depth, shorter pulse width, greater pulse energy and higher peak power. For the dual-loss-modulated QML green laser, at a pump power of 18 W and a repetition rate of 1 kHz, the pulse width and the pulse energy of the Q-switch envelope as well as the peak power of QML green laser are 42.1 ns, 360 microJ and 382 kW, respectively, corresponding to the pulse width compression 62%, the pulse energy improvement 10 times and the QML peak power increase 40 times when compared with that of the singly passively QML green laser.

Diode-pumped passively Q-switched and mode-locked Nd:GdVO 4 laser at 1.34 µm with V:YAG saturable absorber

Using V:YAG as the saturable absorber, a diode-pumped passively Q-switched and mode-locked Nd:GdVO4 laser at 1.34µm is realized. Nearly 100% modulation depth of mode-locking has been achieved. The width of the mode-locked pulse is estimated to be less than 460ps with 125MHz repetition rate within an about 1µs-long Q-switched pulse envelope. A maximum output power of 220mW and Q-switched pulse energy of 10.5µJ is obtained. Using the hyperbolic secant function methods, a fluctuation rate equation model considering the Gaussian distribution of the intracavity photon density and the population inversion in the gain medium as well as the ground-state population intensity of the saturable absorber has been proposed to describe the mode-locking process of diode-pumped Nd:GdVO4/V3+:YAG laser. With the space-dependent rate equations solved numerically, the theoretical calculations reproduce the laser characteristics well.

Watt-level passively Q-switched Er:Lu₂O₃ laser at 2.84 μm using MoS₂.

Efficient diode-pumped passively Q-switched Er:Lu2O3 laser operation at 2.84 μm was realized. A few-layer MoS2 nanosheet film on a YAG substrate, was fabricated and employed as saturable absorber (SA) in a short plane-plane cavity. Under an absorbed diode laser pump power of 7.61 W, an average output power of 1.03 W was generated with a pulse duration of 335 ns and a repetition rate of 121 kHz, resulting in a pulse energy of 8.5 μJ.

Diode-pumped passively Q-switched mode-locked c-cut Nd:GdVO/sub 4//KTP Green laser with a GaAs wafer

A diode-pumped passively Q-switched mode-locked (QML) intracavity frequency-doubled c-cut Nd:GdVO4/KTP green laser with a GaAs saturable absorber is presented. Nearly 100% modulation depth for the mode-locked green pulses has been achieved. By using the hyperbolic secant function methods and considering the influences of continuous pump rate and the stimulated radiation lifetime of the active medium, a modified rate equation model for Q-switched and mode-locked lasers was proposed. With this modified model, the theoretical calculations are in good agreement with the experimental results, and the width of the mode-locked green pulse was estimated to be about 300 ps

First Principles Study on Electronic Structure and Optical Properties of Ternary GaAs:Bi Alloy

The electronic structure and optical properties of ternary GaAs:Bi alloy are investigated by first principles calculations. It is found that the band gap of GaAs1-xBix decreases monotonously with the increasing of Bi concentration, resulting in the fundamental absorption edge and main absorption peaks of GaAs1-xBix shifting toward lower energy with the increase of the Bi content. The optical constants of GaAs1-xBix, such as the optical absorption coefficient, refractive index, extinction coefficient and optical conductivity, are greater than those of pure GaAs when x > 3.1%, but less than those of pure GaAs when x < 3.1%, which is primarily decided by the intraband level repulsions between Bi-induced states and host states on the valence bands; the contribution of Bi-6s, Bi-6p orbitals and Ga-4p, Ga-4s orbitals on conduction bands is also crucial. Bi doping plays an important role in the modulation of the static dielectric constant and the static refractive index. These results suggest a promising application of GaAs1-xBix alloy as a semiconductor saturable absorber.

Pulse Width Reduction in Diode-Pumped Nd:GdVO4 Laser with AO and GaAs Double Q-Switches

By considering the Gaussian spatial distribution of the intracavity photon density, we introduce the rate equations of a diode-pumped Nd:GdVO4 laser doubly Q-switched by acoustic-optic (AO) modulator and GaAs saturable absorber. These rate equations are solved numerically, and the dependence of pulse width on incident pump power is obtained. Meanwhile, a diode-pumped doubly Q-switched Nd:GdVO4 laser with AO and GaAs is realized. This laser can generate a shorter and more symmetric pulse when compared with purely AO and passive Q-switching. The experimental results are in agreement with the theoretical calculations.

Passive Q-Switching of a Laser-Diode End-Pumped Nd:GdVO4 Laser with a GaAs Output Coupler in a Short Cavity

By using GaAs as both an output coupler and a saturable absorber, we demonstrate a laser-diode end-pumped passively Q-switched Nd:GdVO4 laser for the first time to our knowledge. Pulses with widths ranging from 22.8 ns to 119.2 ns and repetition rates ranging from 333 kHZ to 761 kHZ are generated. At the maximum incident pump power of 4.77 W, the maximum average output power of 1.23 W is obtained, corresponding to an optical conversion efficiency of 25.7% and an average slope efficiency of 37.9%. A rate equation model is introduced to theoretically analyze the results obtained in the experiment, in which the Gaussian spatial distribution of the intracavity photon density and the longitudinal distribution of the photon density along the cavity axis are taken into account. The results of numerical calculations of the rate equations are consistent with the experimental results. A further discussion on the pulse repetition rates is presented.

The role of male chromosomal polymorphism played in spermatogenesis and the outcome of IVF/ICSI-ET treatment

Chromosomal polymorphism has been reported to be associated with infertility, but its effect on IVF/ICSI-ET outcome is still controversial. To evaluate whether or not chromosomal polymorphism in men plays a role in spermatogenesis and the outcome of IVF/ICSI-ET, we retrospectively analysed 281 infertile couples. Measures included fertilization rate, implantation rate, pregnancy rate, clinical pregnancy rate, ongoing pregnancy rate, early miscarriage rate and preterm rate. Men with chromosomal polymorphism had significantly higher frequencies of severe oligozoospermia and azoospermia than those without (37.12% vs. 16.11%, p < 0.001; 27.27% vs. 10.74%, p < 0.001; respectively). Significantly, lower fertilization rate (68.02% vs. 78.00%, p < 0.001) and clinical pregnancy rate (45.00% vs. 66.67%, p = 0.031) were observed in polymorphism-carrying men with severe oligozoospermia compared with non-carriers with severe oligozoospermia. This suggests that chromosomal polymorphism has adverse effects on spermatogenesis, negatively influencing the outcome of IVF/ICSI-ET treatment. Polymorphic variations on the Y chromosome have been found to be the most prevalent polymorphism in infertile men, most frequently occurring in patients with severe oligozoospermia.

Diode-pumped doubly passively Q-switched Nd:GdVO 4 1.34μm laser with V 3+ :YAG and Co:LMA saturable absorbers

By simultaneously using V3+:YAG and Co:LMA saturable absorbers in the cavity, a diode-pumped doubly passively Q-switched a-cut Nd:GdVO4 laser at 1.34μm is demonstrated for the first time. The experimental results show that this doubly passively Q-switched laser can generate a shorter pulse width and a higher peak power compared to the singly passively Q-switched laser only with V3+:YAG or Co:LMA saturable absorbers. By considering the thermal lens effect of the laser gain medium, the coupled rate equations for the doubly passively Q-switched laser at 1.34μm under Gaussian approximation are given, and the simulation solutions of the equations are basically identical to the experimental results. The simulation results also show that a doubly passively Q-switched laser can generate a shorter pulse width than a singly passively Q-switched laser even though they have the same initial signal transmissions.