Research Of Fiber Laser Pumped Picosecond Optical Parametric Oscillators

Optical parametric oscillators (OPOs), as important devices for nonlinear optical frequency conversion, are widely used tunable coherent light sources. Especially in the mid-infrared spectral region, optical parametric oscillators are the most promising solid state devices for high power output. Synchronously pumped picosecond OPOs can balance between short pulse duration and narrow spectral linewidth, and have the potential for high average power output. In recent years, with the accelerating development of high power fiber lasers based on large-mode-area double-clad gain fibers, more and more OPOs utilize fiber lasers as the pump source, to obtain improved performance and to meet the requirement of more compact and stable configuration. This thesis presents systematically studies on fiber laser pumped picosecond optical parametric oscillators. Based on the system design, the analysis of output characteristics and the discussion on specific effects and influence factors, we have realized high power widely-tunable mid-infrared OPO, dual-wavelength signal wave OPO and cascaded synchronous terahertz parametric oscillation. The results and conclusions provide useful reference for developing high power all-solid-state mid-infrared lasers and their application. The main contents of this dissertation are listed as follows:Firstly, we design and construct a picosecond optical parametric oscillator pumped by an all fiber master-oscillator power amplifier (MOPA) structured fiber laser. Based on the quasi-phase matching (QPM) technique and the characteristics of PPMgLN crystal, mid-infrared parametric radiation within the spectral range covering 3.15~4.2μm is obtained by temperature tuning and crystal poled period tuning.Influence factors of OPO output characteristics are experimentally investigated and analyzed. Considering the serious broadening of output spectrum from the fiber laser at high power levels, we adopt an approach of multiplying the pulse repetition rate to suppress the nonlinear effects in fiber amplifiers, and eventually achieve output average power as high as 2.64W at 3.42μm, with 11% of the mid-infrared optical-to-optical conversion efficiency.Then, the spectral characteristics of the fiber laser pumped picosecond OPO are investigated comprehensively, based on which the dual-wavelength signal wave is acquired. Because of the broad spectral bandwidth of ultrafast fiber laser, we analyze the parametric gain characteristics under broadband pumping, and numerically simulate the particular case of double-peak spectrum pumping. The condition for dual-wavelength operating is summarized. Experimentally, dual-wavelength signal output is realized and the temperature tuning and output switching methods are studied.Furthermore, cascaded synchronous terahertz optical parametric oscillation in the PPMgLN based OPO is explored. Based on the principle of cascaded parametric processes, cascaded optical parametric oscillation delivering terahertz wave is realized in our picosecond OPO system. We investigate the spectral properties in detail, and the results reveal that this method can be used for the generation of high-repetition-rate ultrafast terahertz wave and has great potential for application.