Study On The Characteristics Of Continuous Wave And Passive Q-switched Laser Of Disordered Garnet Crystal Yb:CNGG

Solid-state laser plays a very crucial role in many application fields. Gain medium is one of the central elements of laser. And laser crystal, the gain medium of solid laser, has been the focus of the studies. The garnet crystal YAG is the most widely used and matures middleware. Nowadays, Yb-doped disordered garnet crystal, such as Yb:CNGG, is arousing the concern of researchers. This kind of laser crystals has high thermal conductivity, which is three times as high as glass and is one-third of YAG crystal. Besides, because of its disordered structure, Yb:CNGG has a considerable inhomogeneous broadening and splitting of energy level, which results in broad absorption and emission bands. The research on the laser property of Yb:CNGG crystal is significant in the development of solid-state laser. In this paper, a simple planoconcave cavity resonator and high-brightness fiber-coupled diode laser were used, we get both continuous wave(CW) and Q-switched pulse laser oscillation with GaAs crystal in the Yb:CNGG disordered garnet crystal with systematic analysis.Under 935 nm diode pumping, an efficient CW laser operation can be demonstrated in the laser experiment with Yb:CNGG crystal. When the cavity length is 3 mm longer than the radius of curvature of the output coupler, we can get the most efficient laser output, which shows the serious thermal effects of Yb:CNGG crystal. In the experiment with different transmissions of output couplers, we find the best transmission is T=5%. The laser efficiency under 975 nm pumping is higher than that under 935 nm pumping. One of the reasons is that the absorption of Yb:CNGG in 975 nm is better than that in 935 nm. And the 975 nm pump wavelength is closed with the 1030 nm output wavelength, which leads to less heat loss according to the quantum defect theory.Efficient laser oscillation in passively Q-switched with GaAs crystal was achieved with Yb:CNGG crystal and the research was analyzed systematically and comprehensively. By comparing the CW and Q-switched laser operation under different transmittance, the efficiency of laser with low transmittance in the case of CW is higher, while the higher transmittance will achieve the better efficient laser in the case of Q-switched. Comparing the laser operation under different cavity lengths, we find that the efficiency of laser with l = 103 mm is better than that with l = 53 mm in the case of CW, but in the case of Q-switched the more stable pulse trains and the larger pulse power were achieved with l = 53 mm. Besides, we also analyzed the process of Yb:CNGG with GaAs systematically and comprehensively. An average output power of 1.76 W is produced at a pulse repetition rate of as high as 166.7 kHz, with optical-to-optical and slope efficiencies of 11.73% and 20%, respectively. The shortest pulse duration achieved was 99.5 ns. We solved the rate equations with Matlab software and the theoretical analysis coincide with the experiment results.