Research On PPLN Quasi-Phase-Matched Mid-infrared External-Cavity Optical Parametric Oscillator

Mid-infrared laser has been widely used in both civilian areas such as spectroscopy, soil testing and military fields such as laser radar and laser guidance due to its good coherence and high resolution. Optical parametric oscillation is an effective method to obtain the mid-infrared laser output, and the development of quasi-phase match technology and periodically poled crystal preparation technology make it easier to achieve high-power and high-efficiency output by the means of optical parametric oscillation. First, in this paper we conduct a research on wavelength-locked laser pumped Nd:YVO4 laser with an output wavelength of 1064 nm,on the basis of which, we conducted the PPLN external cavity optical parametric oscillator experiment.The main content of this paper is introduced as follows:1? A summary of methods to produce the mid-infrared laser and comparison of characters of several nonlinear crystals valid in the mid-infrared laser are demonstrated. The basic principle of quasi-phase match technology is explained. The research progress of the application of mostly used crystals PPLN and PPLT on mid-infrared output is introduced.2? The characters of SRO such as threshold, gain characteristic and conversion efficiency are derived on the foundation of the classic Maxwell's equations with the combination of the theory of oscillation. The tuning curves of PPLN and PPLT are obtained according to corresponding dispersion equations after the deduction of basic principle of quasi-phase match.3? Output power of 28.2W at 1064 nm is obtained by wavelength-locked 878.6nm laser pumping two pieces of concatenated Nd: YVO4 crystal with an efficiency of 70.5%. The disadvantage of low pump absorption of in-band pump is overcome with excellent output power stability.4? Experiment of OPO is conducted using optimized external two-mirror flat-concave resonator with the utility of PPLN crystals working at 140oC. Signal output power of 3.55 W and the corresponding conversion efficiency of 28.4% at 1422 nm are obtained at the grating period of 27.5?m.Idler output power of 1.6W and the corresponding conversion efficiency of 13.2% at 3664 nm are obtained at the grating period of 29?m.