The Research Of Thermal Insensitive Broadband Optical Parametric Amplification Technology For High Power Laser

The generation of high power laser pulse has always been one of the goals pursued by the development of laser technology.In the past two decades,high power lasers have achieved rapid development.High power laser has very important applications in basic scientific research in various interdisciplinary fields such as industrial processing,national security,controlled nuclear fusion,and biochemistry and strong field physics.Optical parametric amplifiers are optical devices based on optical parametric amplification technology to obtain high power laser pulse,which can amplify power of any wavelength laser.Optical parametric amplification is a typical second-order nonlinear optical process and is a basic technology in laser technology.It can expand the working wavelength of the laser and achieve further amplification of the laser output power.It is an important method for generating high power laser pulses.However,in high power optical parametric amplifiers,the unavoidable thermal effect due to the absorption of laser energy by the crystal will greatly reduce the power output of the optical parametric amplification.The laser system that achieves stable high power and ultra-short pulse cannot be separated from the most basic research on optical parameter amplification technology.This article takes optical parametric amplification in high power lasers as the research object and aiming at the existed thermal effect problem in high power optical parametric amplifiers,in order to solve the purpose of thermally induced phase mismatch in the process of high power optical parametric amplification.In terms of improving the conversion efficiency,output power,the gain spectrum thermal stability,broadband characteristics,and spot quality of signal in the process of optical parametric amplification,some related research work has been carried out.The article adopts the research methods of close combination of theoretical calculation analysis and full-dimensional numerical simulation.The main research contents are as follows:1.The optical parametric amplification theory is studied in detail,based on the optical parametric amplification theory,a technical scheme of temperature-insensitive optical parameter amplification based on noncollinear phase matching is proposed.After theoreticalderivation,noncollinear condition for temperature-insensitive phase matching is obtained and the feasibility analysis is verified.Using this condition,the first-order temperature derivatives of three light wave vectors can be eliminated from each other in the specific noncollinear structure of practical application,and the phase matching condition is insensitive to temperature.Therefore,it is convenient to determine the noncollinear angle or suitable nonlinear medium required for temperature-insensitive optical parametric amplification.2.Verify the application prospect of the proposed temperature-insensitive optical parameter amplification technology scheme based on noncollinear phase matching in high power condition.Aiming at two different cases of collinear phase matching and noncollinear temperature-insensitive phase matching schemes,the temperature bandwidth analysis in the cases of small signal and high power condition is studied,and the full-dimensional numerical simulation of the optical parameter amplification process of high power laser is performed.Taking the LBO-based near-infrared optical parameter amplifier at 1030 nm signal and800 nm pump as an example,when the incident pump power is ~120 W,the results show that the conversion efficiency of the temperature-insensitive phase matching scheme can still be maintained at ~35%,which is nearly twice of the collinear phase matching scheme,and a good spot quality output is obtained.From the results,it is realized that the optical parametric amplification process is insensitive to temperature changes.3.Based on the above noncollinear temperature-insensitive phase matching technology,combined with quasi-phase matching(QPM)and noncollinear broadband phase matching,a novel QPM technical scheme of temperature-insensitive broadband optical parametric chirped pulse amplification(OPCPA)based on tilted period polarized crystals is creatively.The design of tilted periodic polarization crystal,feasibility verification and thermal stability analysis of gain spectrum was performed on a typical OPCPA process of 1064 nm pumped 3.4 ?m broadband signal in 5% MgO doped periodically polarized crystal MgO:PPLN.The results show that only satisfy broadband QPM and only satisfy temperature-insensitive QPM can be realized simultaneously in the specific noncollinear structure of noncollinear angle ? = 1.5° and the MgO:PPLN crystal of polarization period ? =3.6 ?m and domain inversion angle ? =79.7 °.And the proposed technical solution has an ultra-broadband gain bandwidth of ~520 nm and excellent gain spectrum thermal stability.4.To verify the application prospect of the proposed general temperature-insensitive wideband optical parametric chirped pulse amplification based on tilted periodic polarized crystal under high power condition,the full-dimensional simulation process was performed.Respectively compared and studied with only satisfy broadband QPM and only satisfy temperature-insensitive QPM schemes,the simulation results show that the proposed scheme can achieve good broadband gain spectrum output of ~380 nm while achieving high conversion efficiency of ~35%.Finally,considering the possible grating errors in practical applications,the effects of grating polarization period deviations in the gain spectrum stability are studied.