Characteristics Of LD–pumped Yb:YAG Thin Disk Laser

LD-pumped thin disk lasers have many merits compared with traditional solid lasers,such as compactness,light weight,good beam quality,steady output characteristics,low cost and long lifetime.They are of great interest in the field of optical communications,micro material processing,holographic technique,nonlinear frequency conversion,and military.Yb:YAG crystal has wide absorption band,long fluorescence lifetime and high quantum efficiency,which makes Yb:YAG become the first choice for the thin disk laser.Cr⁴⁺:YAG passively Q-switching can achieve high repetition rate,short pulse width and high peak power,which has been widely used in passively Q-switched thin disk lasers.Therefore,LD-pumped Cr⁴⁺:YAG passively Q-switched thin disk laser is the focus of laser research.This paper reports the output characteristics of LD–pumped continuous wave and Cr⁴⁺:YAG passively Q-switched Yb:YAG thin disk laser.Firstly,using ANSYS simulates the distribution of temperature in Yb:YAG with direct water cooling,TEC cooling,diamond cooling with different thickness and SiC cooling with different thickness,respectively.Based on the theoretical results,the output characteristics of continuous-wave laser with direct water cooling,TEC cooling and SiC cooling are investigated,the maximum output power up to 2.8 W is obtained with 800 ?m SiC cooling.To further optimize the output characteristics,using different coupling lens and output coupling rates,the experimental results show that when the focal lengths of collimating lens and focus lens is 30 mm and 50 mm,the Yb:YAG thin disk laser can obtain higher power with the output coupling rate of 5%.In the light of the rate equations for Cr⁴⁺:YAG passively Q-switched laser,pulse energy,peak power and pulse width are defined.The initial transmission of Cr⁴⁺:YAG crystal and the reflectivity of output mirror are optimized in theory,using the initial transmission of Cr⁴⁺:YAG crystal of 93% and the reflectivity of output mirror of 90%,a stable pulse train of 1.95 W averaged output power with pulse width of 74 ns and a pulse energy of 1.2 mJ are obtained.The repetition rate is 1.6 kHz,and the beam quality M_x²=1.622,M_y²=1.616.Finnaly,a new method of Q-switching is investigated.Using an electro-optic deflector as a Q-switch,a Nd:YVO₄ laser has been realized.An output pulse train of 1.22 W averaged output power with pulse width of 1.0 ns and peak power of 224 kW is obtained at the repetition rate of 5 kHz.An averaged output power of 2.67 W with pulse width of 2.2 ns and peak power of 60.7 kW is obtained when the repetition rate is 20 kHz.