Research On Amplitude And Amplitude Amplification Technology Of Mid - Infrared Optical Parameters With Narrow Line Width And High Power

Mid-infrared band of3-5μm is widely used in fields of optoelectronic confrontation, atmospheric monitoring, terahertz field generating, free-space optical communications, laser and medical defense, scientific research and civilian. Spectral linewidth narrowing and power enhancing are two vital and promising prospects of mid-infrared lasers driven by application requirements. PPMgLN-OPO based on quasi-phase-matched are significantly favored in high power mid-infrared OPO researches. Limited by the linewidth of pump laser and the high gain under strong pump power, the linewidth of output laser of OPO is relatively wide, typically several nanometers. On the other hand, ulteriorly improving the output power of OPO is astricted by the presumable damage of the nonelinear crystal and mid-infrared film under strong pump power. This particle aims at breaking the bottle-neck on the linewidth narrowing and power scaling.This particle offers theoretical oscillation threshold of single resonance PPMgLN-OPO and its conversion efficiency under different pumping power densities, providing a theoretical basis for the experimental design of high-power PPMgLN-OPO. It includes the theoretical temperature tuning curve of PPMgLN crystal based on energy and momentum conservation equations in three-wave mixing. The analysis of factors causing the central wavelength shifting of parametric light and linewidth broadening is given. And the amount of linewidth broadening is calculated theoretically at experimental wavelength, providing guidance for stabilizing center wavelength and controlling linewidth in experimental researches. By optimizing the parameters of PPMgLN-OPO, we obtained the parametric light output with a high conversion efficiency, verifying the theoretical calculations. When PPMgLN crystal works at105℃, with pumping power of173W, OPO obtained93.6W parametric light output, with a slope efficiency of53.8%. The signal (1.679μm) and idler (2.907μm) output power were respectively65.7W and27.9W.Volμme Bragg gratings are chosen as the key component of narrowing lineidth in OPO. The spectral diffraction efficiency fomula of RBG, derived from Kogelink coupled wave theory, is used to analyze the main factors affecting RBG diffraction efficiency and their correlation. The affections on diffraction efficiency that incident monochromatic wave causes when there lies shift amount of wavelength and incident angle are discussed under gratings’different thickness, spatial frequency and modulation amplitude of the refractive index. A high spectral selectivity RBG produced by OptiGrate is chosen and purchased based on theoretical derivation and calculation to apply parametric light linewidth narrowing experiments on. The pumping source of VBG-OPO is a Q-switch1.064μm Nd:YAG laser. We obtained64.2W parametric light with slope efficiency of37.1%at173W pumping power. The signal(1.679μm) and idler(2.907μm) output power were respectively35.1W and29.1W. The signal linewidth was lnm in free running and was narrowed beneath O.lnm in VBG-OPO. The theoretical idler linewidth is lesser than1.1nm. By adjusting the temperature of VBG and PPMgLN,1.68μm and2.95μm optical parameters can obtained wavelength tuning ranges of3nm and9nm.PPMgLN crystal based OPA technology is analyzed theoretically and experimentally. The variation curve of average power to crystal length in PPMgLN-OPA is calculated. The factors affecting optimum crystal length are analyzed. The results show that when pump and idler wavelength are constant, the greater pumping power and initial idler power are, the shorter optimμm crystal length is. When using44W,1.064μm laser pumped OPA, the4W,2.907μm laser was scaling amplified to12.9W, with a conversion efficiency of20.3%.1W,2.907μm laser was scaling amplified to8.8W with a conversion efficiency of17.1%. When the temperature of PPMgLN crystal in OPA was reduced from the105℃100℃, the conversion efficiency was not significantly changed. The conversion efficiency declined greatly when the temperature of the PPMgLN crystal was further reduced due to the mismatch of temperature.