| 1.4~1.6μm near-infrared radiation and 3~5μm middle-infrared radiation are widely applied in many fields, such as medical treatment, spectroscopy, military and so on. Optical parametric oscillator (OPO) is considered as an efficient method in wavelength extension through non-linear optical frequency conversion. Due to its small scale, high efficiency and tunable output wavelength, QPM-OPO is utilized to emit laser at 1.4~1.6μm and 3~5μm. Intra-cavity singly resonate oscillator (ICSRO) is famous for its continuous-wave (CW) operation and high efficiency, while there are some problems such as instability. In-band pumping can reduce the quantum defect and improve the output characters of ICSRO.This thesis is a study of an all-solid-state CW ICSRO first pumped by a Nd:YVO4 laser at 1064nm under 880nm laser diode (LD) in-band end pumping. A periodically poled lithium niobate (PPLN) was used as the nonlinear medium. A well design of intra-cavity pump scheme and OPO cavity structure made the SRO work with a high efficiency and stable CW operation. Tunable 1.4~1.6μm near-infrared signal output and 3~5μm middle-infrared idle output were obtained with the maximum power of 3.20W and 1.39W respectively. The main contents and innovations are listed as follows:1. Constructed a dynamics model of the multi-modes pumped ICSRO. Through mathematics analysis, an optimization for power performance of signal and idle output was proposed to make a theoretical foundation for ICSRO operation with high efficiency and stable CW.2. Designed the pump laser cavity and OPO cavity. To reduce the affection from thermal lens effects within Nd:YVO4 crystal, and to obtain a stable CW operation and a high beam-quality output, the pump laser cavity and SRO cavity were well designed through a graphic analysis and classic theory of optical resonator design. A lens, which was used as the optical ballast, was applied into the cavity to stabilize the model characters of pump beam in the cavity and make a better mode-volume matching between the LD pump and 1064nm radiation of laser cavity, as well as between the pump and resonating signal of SRO.3. Research on the characters and advantages of 880nm and 885nm in-band pumping. Absorption curve and slope efficiency curve of three Nd:YVO4 crystals with different doped rates were tested under 880nm in-band pumping and 808nm classic pumping respectively. Compared and analyzed their strength and weakness from the output performance based on the two pumping systems, an optimal crystal with doping concentration of 0.5% and length of 10mm was chosen for the next experiment. Output characters of Nd:YAG laser under 885nm in-band pumping and 880nm pumping were also compared.4. Research on the characters of temperature turning and grating period turning of PPLN-OPO under in-band pumping. By changing grating period and temperature of PPLN, tuning range of 1.4~1.5μm in near-infrared eye-safe signal output and 3~5μm in middle-infrared idle output were achieved respectively, well matching the theoretical curves. With 21.9W absorbed pump power and 29μm grating period of PPLN, 3.2W maximum output power at 1.5μm was abtained, correspongding conversion efficiency was 14.6%. Moreover, 1.39W maximum output power at 3.66μm was obtained, corresponding conversion efficiency was 6.3%. Fluctuation of idle output power in an hour is about 1.1% of 880nm in-band pumped ICSRO. |
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