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A compact diode-side-pumped Tm:YAG laser is presented, which can output 51 W of cw power at 2.02μm. The Tm:YAG rod is side pumped by nine diode arrays with the central wavelength of 783nm and the with bandwidth of about 2.5 nm at 25° C. To decrease the thermal effect on the both ends and dissipate the heat effectively, one composite Tm:YAG rod with the undoped YAG end caps and the screw threads on the side surface of the rod is used as the laser crystal. The maximum optical-to-optical conversion efficiency of the 2.02-μm laser output is 14.2%, with a slope efficiency of 26.8%.

The 1319 nm lasers have important applications in the fields of optical fiber communication, laser medical treatment and laser color display. The Nd:YAG laser pumped by 808 nm laser diode is an efficient alternative to achieving 1319 nm laser output. In recent years, direct pump technology using 885 nm laser diodes has become more promising due to the dramatically reduced thermal effect and improved optical conversion efficiency. Quasi-continuous sodium beacon laser with microsecond pulse duration generated by the sum-frequency of 1319 nm and 1064 nm lasers can provide a gatable pulse format to eliminate the interference of atmospheric Rayleigh scattering and mitigate the spot elongation of sodium guide star to improve imaging accuracy. However, relaxation oscillation in the microsecond pulse could cause the damage to the nonlinear crystal and reduce the efficiency of sum-frequency generation. It is effective to suppress the relaxation by taking advantage of second harmonic generation, in which a nonlinear crystal is utilized to reduce the pulse peaks with higher intensity. In this paper, we demonstrate a high-power relaxation-oscillation-free quasi-continuous microsecond pulse 1319 nm laser by using the dual-end 885 nmdiode-pumped three-mirror ring-cavity. Intra-cavity etalon and customized mirror coating are employed to prevent the 1064 nmand 1338 nmline of Nd:YAG laser crystal from oscillating. A power tuning device, including a thin-film polarizer and a halfwave plate is implemented as the output mirror of ring cavity, which enables continuous adjustment of the out coupling ratio. The output power of the 1319 nm polarized laser is 22.5 W pumped by 150 W 885 nm laser diode. The repetition rate is 800 Hz and pulse width is 150 s. The corresponding optical conversion efficiency is 15%. The beam quality factor M2 is measured to be Mx2= 1.35 and My2=1.24. By precisely adjusting the temperature of etalon viz. adjusting refractive index as well as thickness of the etalon material, laser wavelength is tuned from 1318.888 nm to 1319.358 nm, corresponding to a tunable range of 470 pm and tuning accuracy of 0.7 pm. A 1319 nm frequency doubling crystal KTiOPO4 (5 mm5 mm15 mm, = 59:8 and ϕ = 0) is inserted into the cavity to suppress the relaxation oscillation. The pulse waveform quickly reaches a smooth regime, followed by a pulse spike at the initial stage and the loss of laser output power is only 1%. It is proved that it can be efficiently suppressed by inserting a frequency doubling crystal with negligible power loss. In conclusion, this paper provides a practical and effective technical means for achieving the high-power relaxation-oscillation-free quasi-continuous 1319 nm laser with microsecond pulse duration.

Continuous-wave single-frequency 589 nm yellow laser can be used in laser cooling of sodium atoms. Besides, the interaction between 589 nm laser and sodium atoms can be studied by resonance fluorescence, which provides an important basis for the sodium guide star in the adaptive optics. In this paper, single frequency 589 nm yellow light is generated by sum frequency of single-block non-planar ring cavity 1064 nm and 1319 nm laser in periodically poled KTiOPO4 crystal. The geometric parameters of single-block non-planar Nd:YAG crystal and magnetic field intensity are optimally designed by simulation calculation through using Jones matrix. The output powers 1080 mW and 580 mW are obtained for continuous-wave single-frequency 1064 nm and 1319 nm laser in the experiment, respectively The two fundamental beams are expanded to be the same as perfectly as possible in size and are focused into a spot with a size of about 60 m by an achromatic lens. The sum-frequency generation takes place in a 1 mm2 mm20 mm phase-matched type-I periodically poled KTiOPO4 crystal with a matching temperature of 55℃ and polarization period of 12.35 m The crystal is anti-reflection coated for all three wavelengths (1064 nm, 1319 nm and 589 nm). A 14.8 mW output of 589 nm laser is obtained with beam quality factor M2=1.14 and the corresponding sum-frequency efficiency is 0.9%. The influence of periodically poled KTiOPO4 temperature on the sum-frequency efficiency is studied and the temperature acceptance bandwidth is measured to be 1.5 degrees The wavelength of 589 nm yellow light can be tuned to the sodium atom D2a absorption line by changing the temperature of 1064 nm Nd:YAG crystal and 0.164 pm of tuning accuracy is reached. The whole laser system is stable and reliable, so it provides a practical and effective technical means to obtain the continuous-wave single-frequency 589 nm laser, for it is relatively simple and easy to implement.

Ultraviolet laser operating at 355 nm has been found to have wide applications in scientific and industrial fields of laser radar, biological fluorescence medicine, micro processing, laser marking and laser ablation, owing to its superior properties of short wavelength, high single-photon energy, and high resolution. In addition, 355 nm laser plays a vital role in promoting the development of RGB full color display because it can be used as an excitation source for investigating the blue light emitting materials. LiB3O5 (LBO) crystal possesses relatively high nonlinear coefficient and high optical damage threshold. Therefore, it is generally employed to generate 355 nm light through the third harmonic generation (THG) of the Nd:YAG laser (1064 nm). However, the CsB3O5(CBO) crystal, which also belongs to B3O7 group has attracted more attention for its larger nonlinear coefficient. The temperature sensitivity is another important characteristic of the nonlinear crystal. Temperature fluctuation can cause the variation of refractive index of nonlinear optical crystal, which leads to phase mismatch and thus affects the nonlinear conversion efficiency. The principal refractive index of CBO crystal was accurately measured using the auto-collimation method in a temperature range from 40 to 190 ℃ for the first time by Zhang et al. in 2013 [Zhang G C, et al. 2013 Opt. Lett. 38 1594], while the temperature bandwidth of CBO for 355 nm THG has not been reported. In the present paper, a high-power 355 nm laser is produced by efficient THG of an acousto-optic Q-switched quasicontinuous wave 1064 nm laser in CBO crystal. The master-oscillation power-amplification (MOPA) system with Nd:YAG crystal which is side pumped by high-power pulsed laser diode (LD) array delivers 210 W of a quasi-continuous Q-switched 1064 nm laser power. The laser operates at a 1 kHz repetition rate, and each pulse train contains five Q-switched pulses each with a duration of 40 ns. The 98 W of 532 nm green light is produced by second-harmonic generated in type-I LBO crystal. The 28.3 W ultraviolet laser is achieved by a 30-mm type-II CBO crystal through the sum frequency of 1064 nm and 532 nm light. The conversion efficiency from the fundamental light to the third harmonic reaches 13.5%, which is 28.6% higher than that obtained with a type-II LBO crystal under the same experimental conditions. The temperature sensitivity of CBO crystal in the 355 nm THG process is studied. Its temperature bandwidth is 25, which is much broader than that of LBO crystal. The experimental results show that the CBO crystal is superior to LBO crystal in the sense of conversion efficiency and temperature sensitivity for THG of 355 nm.

A high-efficiency high-power Nd:YAG laser under 885nm laser diode (LD) pumping is demonstrated. The laser crystal is carefully designed, and the overlapping between the pump modes and the laser modes is optimized. The maximum output power at 1064 nm is 87W under the absorbed pump power 127.7W, corresponding to a slope efficiency of 72.4% and an optical-optical efficiency of 68.1%. The optical-optical efficiency is 58.4% for the pump power emitted directly from the LD. To our best knowledge, this is the maximal optical-optical conversion efficiency obtained for the LD end-pumped Nd:YAG lasers so far.

Laser performance of 1064 nm domestic Nd:YAG ceramic lasers for 885 nm direct pumping and 808 nm traditional pumping are compared. Higher slope efficiency of 34% and maximum output power of 16.5 W are obtained for the 885 nm pump with a 6 mm length 1 at.% Nd:YAG ceramic. The advantages for 885 nm direct pumping are discussed in detail. This pumping scheme for highly doping a Nd:YAG ceramic laser is considered as an available way to generate high power and good beam quality simultaneously.