低阈值宽调谐的内腔调QNd∶YVO_4/PPLN光学参量产生

将多周期极化铌酸锂(PPLN)晶体置于激光二极管(LD)端面抽运的声光调QNd∶YVO4激光器谐振腔内,实现了准相位匹配内腔光学参量直接产生(QPM-IOPG)。PPLN晶体长20 mm,利用外加电场极化法制作,极化沿晶体的z向进行。设定声光Q开关重复频率为19 kHz,通过温度调谐和周期调谐,获得了信号光在1384~1541 nm范围内的连续输出,脉冲宽度约为80 ns。在PPLN晶体温度为140℃,极化周期为29μm时,内腔光参量产生的阈值仅为0.93 W,在3 W激光二极管抽运功率下,获得了140 mW的信号光输出;在极化周期为26.5μm时,内腔光参量产生的阈值增大到1.36 W,在3 W激光二极管抽运功率下,获得了105 mW的信号光输出。分析了不同极化周期下阈值和转换效率存在差异的原因,对内腔光学参量产生的阈值进行了理论分析和计算。

Low-Threshold Widely-Tunable Intracavity Q-Switched Nd∶YVO4/PPLN Optical Parametric Generator

A quasi-phase-matched intracavity optical parametric generator (QPM-IOPG) is demonstrated based on multi-grating periodically poled lithium niobate (PPLN) internal to an acousto-optically Q-switched Nd∶YVO4 laser. The PPLN crystal is 20 mm long and periodically poled along the z-axis by using external electric poling technique. While the Q-switch repetition rate is set at 19 kHz, the signal wavelength can be continuously tuned from 1384 nm to 1541 nm by combining temperature tuning and grating tuning. The measured signal pulse width is approximately 80 ns. While the PPLN crystal temperature is 140 ℃, the QPM-IOPG threshold is just 0.93 W with the 29 μm grating period and 3 W of laser diode (LD) pump power produces 140 mW signal output. With the 26.5 μm grating period, the QPM-IOPG threshold is increased to 1.36 W and at an incident LD pump of 3 W, 105 mW signal is obtained. The reason of the different thresholds and conversion efficiencies for various grating periods is analyzed and the theoretical calculation of the QPM-IOPG threshold is also presented.