Dongsheng Wang

183 WTEM00 mode acoustic-optic Q-switched MOPA laser at 850 kHz.

We report a high-power, high-repetition-rate TEM00 mode MOPA laser using acoustic-optic Q-switching. Seed laser from the dual-end- pumped Nd:YVO4 oscillator was scaled up to 183.5 W average power at 850 kHz after behind amplified by the four-stage power amplifiers. The stable Q-switching operation worked at different pulse repetition rate from 60 kHz to 850 kHz while the pulse duration increased from 12.8 ns to 72 ns. The beam quality was near diffraction-limit with M2 factors measured as M2x = 1.28 and M2y = 1.21. In CW operation, 195 W TEM00 mode output was achieved corresponding to the total optical-optical efficiency of 44.7% and the absorbed pump power to output power efficiency of 53.3% respectively.

A 108W, 500 kHz Q-switching Nd:YVO 4 laser with the MOPA configuration

A high power, dual-end-pumped Nd:YVO(4) laser with a MOPA configuration was stably Q-switched at repetition rate up to 500 kHz. The thermally bonded Nd:YVO(4) crystal was used in our experiment. In acousto-optically Q-switching operation at repetition rate of 500 kHz, 35 W average power was produced by the oscillator, with optical-optical efficiency of 41.7%. 108 W average power was obtained by a master oscillator power amplifier (MOPA) configuration including two amplifier stages, corresponding to the total optical-optical efficiency of 42.2%. The pulse duration was 48 ns, with a stability of pulse peak value < 2.5%. The beam quality was better than two-times diffraction-limit (M(x)(2) = 1.99, M(y)(2) = 1.76).

103 W high beam quality green laser with an extra- cavity second harmonic generation.

We demonstrated a 103.5 W green laser with an extra-cavity second harmonic generation. The IR source was a high power Q-switched Nd:YVO(4) MOPA laser. The type I phase-matching LiB(3)O(5) was used as the nonlinear crystal in the second harmonic generation. The 103.5 W average power of 532 nm green laser was obtained at a repetition rate of 60 kHz with the beam quality factors of M2x <1.44 and M2y <1.23 in the orthogonal directions, corresponding to a peak power as high as 1.5 MW with the instability of pulse energy less than +/-4%. The optical frequency conversion efficiency from IR to green laser was up to 67%.

Comparative investigation on performance of acousto-optically Q-switched dual-rod Nd:YAG-Nd:YVO(4) laser and dual-rod Nd:YVO(4)-Nd:YVO(4) laser.

We demonstrated an acousto-optically (AO) Q-switched dual-rod laser with different gain crystals in the cavity, the combination of Nd:YAG crystal and Nd:YVO(4) crystal. An AO Q-switched dual-rod Nd:YVO(4)-Nd:YVO(4) laser was also configured for comparative investigation. A 69 and 75?W near diffraction-limited laser in CW operation was obtained for the dual-rod Nd:YAG-Nd:YVO(4) laser and dual-rod Nd:YVO(4)-Nd:YVO(4) laser, respectively. In the Q-switched operation, 500?kHz output with 64.2?W average power and 650?kHz laser with 73.2?W average power was achieved for the Nd:YAG-Nd:YVO(4) laser and Nd:YVO(4)-Nd:YVO(4) laser, respectively. The detailed comparison on the performance of pulse duration, pulse repetition rate, output power, and optical spectrum was also investigated and discussed.

High repetition rate dual-rod acousto-optics Q-switched composite Nd:YVO4 laser.

We demonstrate the high-repetition rate acousto-optic Q-switching of a dual-rod Nd:YVO4 laser. Two thermally bonded composite YVO4-Nd:YVO4-YVO4 rod crystals were used as the gain medium to reduce the serious thermal effect. The pump mode and its influence on the laser mode were analyzed, and the effective pump radius was controlled by tuning the spectrum of laser diodes with adjustment on the temperature of laser diodes. Three different configurations of cavity optics were designed and the output performance using these cavities was investigated. In Q-switching operation, 73.2 W TEM00 mode average power at 650 kHz was obtained. The stable Q-switching range was from 80 kHz to 650 kHz with the pulse duration increasing from 17.5 ns to 80 ns. In CW operation, 78 W TEM00 mode and 93 W multi-mode output power was achieved with different cavity designs, corresponding to the optical-optical efficiency of 46.5% and 52.2% respectively.

2 MHz AO

We present a detailed experimental and theoretical study of the ultrahigh repetition rate AO Q -switched TEM00 grazing incidence laser. Up to 2.1 MHz Q-switching with TEM00 output of 8.6 W and 2.2 MHz Q -switching with multimode output of 10 W were achieved by using an acousto-optics Q -switched grazing-incidence laser with optimum grazing-incidence angle and cavity configuration. The crystal was 3 at.% neodymium doped Nd:YVO4 slab. The pulse duration at 2 MHz repetition rate was about 31 ns. The instabilities of pulse energy at 2 MHz repetition rate were less than plusmn6.7% with TEM00 operation and plusmn3.3% with multimode operation respectively. The modeling of high repetition rate Q-switched operation is presented based on the rate equation, and with the solution of the modeling, higher pump power, smaller section area of laser mode, and larger stimulated emission cross section of the gain medium are beneficial to the Q-switched operation with ultrahigh repetition rate, which is in consistent with the experimental results.

Q

A master oscillator power amplifier (MOPA) Nd:YVO4 laser with a controllable gain distribution was built up in our experiment. With the gain guiding effects, the final beam quality of the MOPA system with two amplification stages was near-diffraction-limited (M2≈1.2) compared with M2≈2.5 in the master oscillator, and the total extraction efficiency of amplifier stages was up to 44% corresponding to a 107 W laser output. The enhancement of the beam quality during the amplifying process was also observed in the other two MOPA lasers with the optimal gain adjusting, a MOPA laser containing a Nd:YVO4 seed laser and four Nd:YVO4 amplifier stages, and another MOPA laser containing a Nd:yttrium aluminum garnet acoustic-optic cavity dump pulsed seed laser and four Nd:YVO4 amplifier stages. It has been shown for the first time to our knowledge that not only the power scaling can be realized in the MOPA configuration, but the beam quality can be enhanced as well because of the gain guiding effects.

-switched

A theoretical model as well as the experimental verification of the combined guiding mechanism for the transverse mode formation in the end-pumped laser resonator are investigated. The nonlinear Schrödinger-type wave equation in the gain medium is derived, in which the combined guiding mechanism: the thermal induced refractive index guiding effect as well as the gain guiding effect, is taken into account. The gain saturation and spatial hole burning are considered. The split step Fourier method is used to solve the nonlinear wave equation. A high power end-pumped Nd:YVO4 laser resonator is built up. After establishing the pump absorption model of our laser resonator, the temperature distribution in the gain medium is obtained by the numerical solving of the heat diffusion equation. The combined guiding effect is first observed in the end-pumped Nd:YVO4 laser resonator, and the experimental transverse mode profiles well agree with the theoretical prediction from the derived nonlinear Schrödinger-type wave equation. The geometric design criterion of the TEM00 mode laser is compared with our wave theory. The experimental- and theoretical- results show that our wave theory with the combined guiding mechanism dominates the transverse mode formation in high power end-pumped laser resonator.

{\rm TEM}_{00}

Abstract This study demonstrates a diode side-pumped Yb:YAG laser operated under free-run and passively GaAs Q-switched conditions. The maximal output energy was 10 mJ at a 25 Hz pulse repetition frequency (PRF) with a 1ms pump pulse duration when free-running condition. The GaAs wafer was used both as a passive Q-switch and a Brewster plate. Pumped by 175 mJ of 1 ms pulse duration at 941 nm, the laser outputted 13 pulses at 1.03 μm when under the Q-switched. The first pulse was 120 ns with a peak power of 83 W. Rate equations were calculated and the passive Q-switching theory was analyzed. The equations’ numerical solutions were in good agreement with the experimental results.

Grazing Incidence Laser With 3 at.% Neodymium Doped Nd:YVO

Walk-off compensation using wedged cut type-II LBO was investigated theoretically and experimentally. An algorithm is proposed to find the optimized wedged cut angle to compensate the walk-off effect completely. Using a pulsed Nd:Y V O4 MOPA laser as the fundamental frequency infrared (IR) source, 36.3xa0W 355xa0nm frequency converted ultraviolet (UV) light was obtained using an optimized wedged cut type-II LBO for walk-off compensated third-harmonic generation (THG), giving a conversion efficiency of 37.1% from IR to UV. A comparative experiment using a conventional cut type-II LBO was also implemented. The results indicate that optimized wedged cutting of type-II LBO is an effective approach for walk-off compensation in efficient THG. The output performance of angle and temperature tuning for wedged cut type-II LBO was also investigated.