Study On Ho:YLF Laser And Its Frequency Conversion

The 3?5mm mid-infrared laser is in the atmospheric window and plays an important role in laser communications,laser medical treatment,environmental monitoring,remote sensing,and optoelectronic countermeasures.At present,the mid-infrared technology produced by the optical parametric oscillator(OPO)has the advantages of wide tuning range,high output power,narrow laser line width,and small volume.In this paper,two schemes was mainly used to generate mid-infrared lasers.One is to generate a 2050 nm laser by a 1940 nm laser pumping the Ho:YLF solid-state Q-switched laser,and this laser is used to pump ZGP-OPO to produce mid-infrared.The other is to amplify 1064 nm seed light by optical fiber master oscillator power-amplifier(MOPA),and use this amplified seed light to pump MgO:PPLN-OPO after collimate and focus to generate mid-infrared laser.In theoretical research,the three-wave coupling equation in the nonlinear medium in the OPO cavity was introduced.The principle of angle phase matching and quasi-phase matching was analyzed.The theoretical basis of Ho laser was studied,and the wavelength tuning of ZGP crystal and MgO:PPLN crystal was studied.The effects of single-resonance OPO thresholds,conversion efficiencies,and different polarization couplings on conversion efficiency was studied.The basic concepts and principles of MOPA were briefly introduced,and the effect of reverse Brillouin scattering on the output laser in an optical fiber was studied.The principle of propagation of a Gaussian beam in an OPO resonator was analyzed.In the experimental study,the line polarization light of 30 W was obtained through the optical fiber MOPA experiment,and its slope efficiency was 45%.Using this line polarized light to pump MgO:PPLN-OPO,a final output of 3.8 W of 3860 nm mid-infrared idle light was obtained.The optical-optical conversion efficiency was about 13.7%,and the temperature tuning of the MgO:PPLN crystal was achieved by changing the temperature.The wavelength range of the temperature variation range from 40°C to 200°C was 3944-3746 nm.