Research On Laser Characteristics Of Yb³⁺-doped Sodium Yttrium Tungstate Crystals

In recent years, with the rapid development of high-brightness and high-power In Ga As laser diode(LD), many researchers are gradually interested in the laser crystal doped by ytterbium(Yb3+), which adopted to generate ultrashort laser pulse. The Yb3+doped high power ultrafast solid-state lasers have the advantages of high conversion efficiency, reliable performance, good noise characteristics, high frequency stability, high output power, easily integrated and compact structures. It is widely used in many areas including industrial cutting,laser weapons, laser communications and scientific research.In this paper, solid-state laser performance of Yb:Na Y(WO4)2(Yb:Na YW) crystal was studied comprehensively. Fiber-coupled semiconductor laser was used as pump source and Yb3+-doped Na Y(WO4)2 laser crystal as gain medium. The Yb:Na YW laser performances of continuous, Q-switched, the chamber emptied, Q-switched and mode-locked, continuous mode-locked were investigated.1. Firstly, the advantages and applications of solid-state lasers were summarized, and the characteristics and advantages of the Yb3+and Yb3+doped laser crystals were introduced,and the research status and progress of Yb3+-doped solid-state lasers were reviewed.2. The Yb:Na YW crystal structure and laser characteristic were studied systematically:The crystal growth,crystal properties and the progress of Yb:Na YW solid-state lasers were summaried. Then Yb:Na YW crystal laser characteristics in 1μm band was studied, the power and spectral characteristics were analyzed. The maximum output power of 1.1W was obtained when the pump power was 6.23 W and the output coupler was 5%. The corresponding slope efficiency and the optical-to-optical efficiency were determined to be34.5% and 17.7%. The output beam was linearly polarized. There were as many as five obvious emission branches located from 1044 nm to 1051 nm for T=5%, or from 1054 nm to1060nm for T=1%.3. The dynamic influence of the different modulation devices on the building of the Q-switched pulses had been investigated. Acousto-optic modulator was used to achieve the active Q-switched of Yb:Na YW laser. At the repetition rate of 10 k Hz, when the pump power was 8.6W, laser average output power was 180 m W, the pulse width was 398 ns. So the single pulse energy and peak power were calculated to be 18μJ and 0.044 k W. The RTP electro-optical modulator was used to achieve cavity-dumped Yb:Na YW crystal laser. The obtained average output power was 42.1m W. When pump power and repetition rate increased, the pulses width were unchanged, the stable pulses were 5.3±0.4ns. By inserting the Mo S2 saturable absorber into a plano-concave cavity of Yb:Na YW laser, stable passively Q-switched laser operation was obtained. In passively Q-switched case, at the absorbed pump power of 10.37 W,the maximum average output power was 70 m W,the shortest pulse width was 426 ns and the pulse repetition rate was 135 k Hz, so the maximum pulse energy was 0.52μJ with the peak power of 1.2W.4. In the Z-folded cavity, by using Yb:Na YW as the laser medium, a diode-pumped active Q-switch mode-locked laser with an AO modulator was realized.In the acousto-optic(AO)QML, a maximum average output power of 203 m W was obtained under an absorbed pump power of 8.6W, corresponding to a slope efficiency of 6.5%.5. With optimum resonator design, the stable SESAM continuous-wave mode-locked Yb:Na YW laser had been realized. Transmissive SESAM was used to achieve the Yb:Na YW mode-locked laser operation. In the CW mode-locked mode, a maximum average power of 164 m W was obtained under the incident pump power of 8.6W. The pulse duration was measured to be 246 fs with a repetition rate of 35 MHz. The mode-locked pulse energy was 4.7n J with the peak power of 19.1k W. Reflective SESAM was used to achieve femtosecond mode-locked Yb:Na YW laser. A maximum average power of 780 m W was obtained under the incident pump power of 7.83 W. The pulse duration was measured to be524 fs with a repetition rate of 92.5MHz. The mode-locked pulse energy was 8.4n J with the peak power of 16 k W.