Research On Continuous-wave Tunable Intra-cavity Ppln-opo Operating At Mid And Near Infrared

Radiation in 1.4~1.6μm near-infrared eye-safe region and 3~5μm mid-infrared region have important application background in spectroscopy, medical treatment, instance remote sensing and Doppler lidar systems. In recent years, driven by improvements in fabricating of periodically poled lithium niobate (PPLN) crystal and all-solid-state laser technology, quasi-phase-matching optical parametric oscillator (QPM-OPO) became efficient method to obtain output in these two regions.This dissertation is concentrated in research of an all-solid-state continuous-wave (CW) intra-cavity singly resonate oscillator (ICSRO) which utilized 808nm laser diode end pumped Nd:YVO4 laser operating at 1064nm as pump source and PPLN as nonlinear medium. Efficient, low threshold CW operation of the SRO was realized though intra-cavity pump scheme and carefully cavity design. Tunable near-infrared signal output in eye-safe region with 2.21W maximum power and mid-infrared idle output with 960mW maximum power were obtained. The main contents and key innovative points are as follows:1. Based on analysis of the dynamics model of multi-modes pumped ICSRO, the methods to optimize power performance of signal and idle output were given through mathematics analysis, which are theoretical basis for high efficiency, low threshold CW operation of the SRO.2. To overcome thermal lens effect's affection on the transmission of pump beam thus realize efficient, stable operating of the SRO and obtain output with high beam-quality, the pump laser cavity was designed in detail as a thermal-insensitive resonator based on graphic analysis and design method of optical resonator and measured thermal focal length.3. The transmissions of pump and signal beams in the cavity were simulated and the cavities were designed for well mode matching in the two conversion processes of lasing and OPO. This helps decrease diffraction loss, low down the threshold and increases the efficiency.4. Temperature and grating period turning curves of PPLN-OPO were calculated. Experimental tuning range were 1401~1513nm for near infrared eye-safe signal output and 3.66~4.22μm for mid-infrared idle output, which matched theoretical curves well. When the LD pump power was 17.1W, the maximum signal output power was 2.21W at 1500nm, with a conversion efficiency of 12.9%. For the idle output, it was 960mW at 3.66μm, the conversion efficiency was 5.6%; 25.4% of incident 808nm pump photonics finally converted to mid-infrared output.