Kejian Yang

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.

Diode-pumped continuous wave tunable and graphene Q-switched Tm:LSO lasers

We have investigated the lasing characteristics of Tm:LSO crystal in three operation regimes: continuous wave (CW), wavelength tunable and passive Q-switching based on graphene. In CW regime, a maximum output power of 0.65 W at 2054.9 nm with a slope efficiency of 21% was achieved. With a quartz plate, a broad wavelength tunable range of 145 nm was obtained, corresponding to a FWHM of 100 nm. By using a graphene saturable absorber mirror, the passively Q-switched Tm:LSO laser produced pulses with duration of 7.8 μs at 2030.8 nm under a repetition rate of 7.6 kHz, corresponding to pulse energy of 14.0 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

12-W red light generation by frequency-doubling Q-switched Nd:YAG laser

By using a 15 mm-long type I phase-matching LBO crystal, a maximum quasi-continuous wave red laser output power of 12 W has been obtained by intra-cavity second-harmonic generation (SHG) in a compact acousto-optically Q-switched diode-side-pumped Nd:YAG laser. The corresponding optical-optical conversion efficiency is 6.6%. The power instability at the maximum output power is observed to be less than 4.62% during half an hour. The beam quality factor M2 is measured to be 9.9 ± 1.0 by the knife-edge method. The spectrum of the red radiation is also measured and discussed.

A diode-pumped passively Q-switched Tm,Ho:YAP laser with a single-walled carbon nanotube

In this letter we present diode-pumped continuous wave (CW) and passively Q-switched a-cut and b-cut Tm,Ho:YAP lasers with a single-walled carbon nanotube saturable absorber (SWCNT-SA). In the CW regime, a maximum output power of 1.61 W at 2118.3 nm corresponding to a slope efficiency of 33.7% and a maximum output power of 1.23 W with a slope efficiency of 28.7% at 2129.6 nm were achieved from the a- and b-cut Tm,Ho:YAP lasers, respectively. With a SWCNT employed as the saturable absorber, passively Q-switched a- and b-cut Tm,Ho:YAP lasers were both realized. The a-cut Tm,Ho:YAP laser generated a 245 ns pulse at 2128.3 nm with a repetition rate of 400 kHz, while the b-cut Tm,Ho:YAP laser produced a 135 ns pulse at 2130 nm with a repetition rate of 245 kHz.

Passively Q-switched laser performance of a diode-pump mixed Nd:Lu0.15Y0.85VO4 crystal

A diode-pumped passively Q-switched Nd:Lu0.15Y0.85VO4 laser with a GaAs output coupler is demonstrated. By using a mixed crystal Nd:Lu0.15Y0.85VO4 as laser medium, the passively Q-switched laser can generate shorter pulse width with higher peak power in comparison with the passively Q-switched Nd:LuVO4 or Nd:YVO4 lasers under the same laser cavity. At the incident pump power 11.9 W, the minimum pulse width of 3.23 ns and the maximum peak power 1.67 kW can be obtained. The average output power and the pulse repetition rate of the laser are also measured. The experimental results show that the mixed crystal is a promising laser medium for shorter Q-switched pulse with higher peak power.

Investigation of a diode-pumped double passively Q-switched Nd:GdVO4 laser with a Cr4+: YAG saturable absorber and a GaAs coupler

A diode-pumped double passively Q-switched Nd:GdVO4 laser with a Cr4+:YAG saturable absorber and a GaAs coupler is realized for the first time to our knowledge. This laser can generate symmetric pulse temporal profiles and shorter pulses with higher peak powers when compared with the single passively Q-switched laser. To understand the results obtained in the experiment, we introduce a rate equation model in which the spatial distributions of the intracavity photon density, the pump beam and the population-inversion density are taken into account. The numerical solutions of the rate equations are consistent with the experimental results.

Simultaneous mode locking in an acousto-optic Q-switched Nd:LuVO4 laser

Simultaneous mode locking had been obtained in acousto-optic Q-switched Nd:LuVO4 laser by using a Z-type cavity. Pulses with great average output power and narrow pulse width were observed in our experiment. The modulation depth is nearly 90% and the width of Q-switched envelope is about 70 ns, and both maintained constant with the increase of pump power. The maximum average output power of 1.83 W was obtained when the incident pump power was 6.78 W and the Q-switched envelop repetition frequency was 30 kHz. Also the average pulse width of the mode locking among the Q-switched envelope is estimated to be about 200 ps.

Optimization of peak power of doubly Q-switched lasers with both an acousto-optic modulator and a Cr4+-doped saturable absorber

A doubly Q-switched laser can obtain a shorter pulse with a stable repetition rate and high pulse peak power, which has been experimentally proved. By taking into account the Gaussian spatial distributions of the intracavity photon density and the initial population-inversion density as well as the influence of the acousto-optic (AO) Q switch, we introduce the coupled rate equations for a doubly Q-switched laser with both an AO modulator and a Cr(4+)-doped saturable absorber. These coupled rate equations are solved numerically. The key parameters of an optimally coupled doubly Q-switched laser are determined based on maximizing the peak power, which include the optimal normalized coupling parameter, the optimal normalized saturable absorber parameters, and the normalized parameters of the AO Q switch. The optimal normalized peak power, the corresponding normalized energy, and the normalized pulse width are also given, and a group of general curves are generated for the first time to our knowledge. The curves can give us a good understanding of the dependence of the optimal key parameters on the parameters of the gain medium, the saturable absorber, the AO Q switch, the resonator, and the spatial distributions of the intracavity photon density. The optimal calculations for a diode-pumped Nd(3+):YVO(4) laser with both an AO modulator and a Cr(4+):YAG saturable absorber are presented to demonstrate the use of the curves and the related formulas.

Compression of pulse duration in a laser-diode, end-pumped, double Q-switched laser.

By considering the Guassian transversal distribution of intracavity photon density and the longitudinal distribution of photon density along the cavity axis as well as the influence of the turn-off time of the acousto-optic Q switch, we introduce the coupled rate equations of a laser-diode, end-pumped, double Q-switched laser with an acousto-optic modulator and GaAs saturable absorber. In addition the thermal effect of the gain medium is taken into account. These coupled rate equations are solved numerically, and the dependence of pulse width on incident pump power at different pulse repetition rates is obtained for the generated output pulses. It is shown that the pulse duration is obviously shorter in contrast to the actively Q-switched Nd:YVO4 laser with an acoustic-optic modulator, and the maximum compression ratio of the pulse width is more than 60%. In the experiment a laser-diode, end-pumped, double Q-switched Nd:YVO4 laser with both an acousto-optic modulator and GaAs is realized, and the experimental results agree with the numerical solutions.