Research Of Fiber Laser Pumped Continuous-wave Optical Parametric Oscillator

Optical parametric oscillator(OPO) is one of the most important ways to get widely continuous-tunable lasers. It has important applications in infrared countermeasures, optical communications systems, remote sensing and spectroscopy, and other research fields. Diode-pumped solid-state lasers are the most common OPO pump source. When operating at high power, such lasers with complex heat sink, in order to reduce the thermal effect. This is not conducive to the practical use of the OPO in compact structure, system complexity and other requirements. Conversion efficiency of the fiber laser is higher than diode-pumped solid-state laser. This makes it significantly reduces cooling demand with other solid-state lasers in the same output power conditions. This makes the use of fiber laser pumped OPO system can be reduced in size under the premise get a higher conversion efficiency of the laser output.The periodically poled technology matures makes the QPM continuous wave optical parametric oscillator realized the magnitude of watt infrared output. Using cascaded parametric oscillation, we obtained the terahertz wave output. The major research problem is to use the advantage of the fiber laser as the pump source to a continuous wave optical parametric oscillator, by adjusting the output power of high-performance pump source, the temperature of the crystal polarization, period, cavity length and other parameters, to obtain high output power, tunable wavelength range, and compact tunable light source. In this paper, through theoretical analysis, numerical simulation and experimental research and other means, a continuous wave optical parametric oscillator pumped by fiber laser was carried out related research of wide-tunable high-power continuous-wave mid-infrared OPO and cascade terahertz parametric oscillator. The study has important theoretical significance and reference value for the engineering application of high-power solid-state mid-infrared and terahertz radiation source and its application technology development. The main contents of this dissertation are listed as follows:Firstly, continuous wave parametric oscillator characteristics were analyzed through numerical simulation method. Analyzed the two major thermal effects among high power continuous wave OPO used Mg O: PPLN crystal by the finite element analysis method: thermal lensing and thermally induced phase mismatch effects. The results showed that: On Mg O: PPLN crystal and two mirrors linear cavity, working at room temperature, the pump wavelength of 1.064 μm, the signal light output range of 3.3 ~ 3.4 μm, thermal lens effect is relatively small when the pump power is less than 50 W. The greater the signal light output coupling, thermal induced phase mismatch effects have become smaller. By the pump power of 100 W, the relative conversion efficiency under full phase-matched reduced by nearly 10%.Next, the output power characteristics of two mirrors linear cavity structure for mid-infrared optical parametric oscillator were studied comprehensivly. We got the output wavelength of 3.414 μm idler by 49 W linearly polarized pump powers. Its maximum output power was 12.09 W with the quantum conversion efficiency of 79.2%. And we also obtained the output wavelength of 3.81μm with the maximum idler power of 4.25 W and 31.1% of the quantum conversion efficiency. We also achieved a continuously tunable output in 3248 ~ 3820 nm wavelength range. Based on the above study, we further developed the four-mirror linear cavity and the ring cavity structure OPO experimental study. We presented the experimental design and analysis process and accessed to the relevant characteristics of the power output.Then, we derived the cascade process of continuous wave parametric oscillation plane wave analysis model. The calculated threshold of backward parametric process by the model was consistent with the reverse experimental reports. The results showed that: for the crystal period between 24 um to 30 um, the threshold of forward parametric process was 2.2 ~ 2.4 times of the backward parametric process. When the cascade of parametric frequency conversion process was less than 6, the energy conversion efficiencies was the order of 10-4 to 10-5 range. The energy conversion efficiency of the high order cascade parametric process was greater than non-cascaded nonlinear parametric process limited by Manley-Rowe relationship.Finally, we carried out relevant experimental studies of cascaded parametric process produced a continuous cascade terahertz by two mirrors line cavity OPO. We obtained the frequency shift with respect to the original signal light, respectively 47,94, and 104 cm-1, corresponding to the center frequency of the signal light, respectively: 1487.0 nm, 1497.5 nm and 1499.7 nm. By combining theoretical analysis of experimental data, we obtained the output of the THz wave around 1.4 THz and 3.1 THz. Studies have shown that effective control of the pump linewidth optical parametric oscillator for the cascade effect is the key factor to increase the number of cascaded parametric oscillation.