Study On Narrow Linewidth Dual-wavelength Mid-infrared Laser Based On Intracavity Pump MgO:APLN

In recent years,mid-infrared dual-wavelength laser technology has been widely used in various fields,such as biomedical detection,chemical sensors,terahertz wave emitters and differential absorption lidar.At present,there are many ways to obtain mid-infrared dual-wavelength laser,and the multi-optical parametric oscillator(MOPO)using a single aperiodically polarized lithium niobate(MgO:APLN)crystal has attracted wide attention because of its high integration and controllable gain.However,due to the limitation of the bandwidth of the crystal gain spectrum and the width of the pumping light,the linewidth of the mid-infrared dual-wavelength laser output by MOPO is wide without using the linewidth compression device,so it is difficult to meet the requirements of high-precision application.This paper will focus on the key problem of further narrowing the linewidth of infrared dual-wavelength laser in MgO:APLN multi-optical parametric oscillator,and carry out related theoretical and experimental research.Theoretical aspects:firstly,according to the phase matching principle of three-wave mixing,the reasons of phase mismatch and linewidth broadening caused by parametric light passing through nonlinear crystal once are analyzed,and a scheme of using F-P etalon to narrow the signal light width and indirectly solve the problem of linewidth broadening of two idle light beams is proposed.Then,according to the law of conservation of energy,the relationship between a single set of signal light and idle light is analyzed theoretically,and based on the five-wave coupling equation,the relationship between two sets of parametric light is analyzed theoretically,and then the theoretical optimal compression value of F-P etalon to narrow the width of two signal lights is obtained.Finally,according to the frequency selection principle of F-P etalon,the optimal parameters of F-P etalon for narrowing the linewidth of mid-infrared dual-wavelength laser are determined,and the cavity structure parameters of narrow linewidth multi-optical parametric oscillator are optimized by combining the cavity structure design theory.Experimental aspects:firstly,the experimental study of mid-infrared dual-wavelength multi-optical parametric oscillator based on intracavity pumped MgO:APLN is carried out,and the linewidths of 3.30μm and 3.84μm lasers are 2.98 nm and 3.15 nm respectively.Then,through the linewidth narrowing experiment of single F-P etalon,the linewidths of3.30μm and 3.84μm laser after narrowing are 0.73 nm and 0.81 nm respectively.In order to further suppress adjacent modes,the linewidth narrowing experiment of combined F-P etalon is carried out,and the linewidths of 3.30μm and 3.84μm lasers without adjacent modes are 0.71 nm and 0.79 nm respectively.The maximum total output power is 2.87 W,in which the maximum output power of 3.30μm and 3.84μm is 0.98 W and 1.89 W respectively,and the corresponding conversion efficiency is 2.24%and 4.31%respectively.The beam quality factors M~2 in the x and y directions of 3.30μm are 1.43 and 1.47,and M~2in the x and y directions of 3.84μm are 1.45 and 1.46,respectively.