Research On Orthogonally Polarized Dual-wavelength Solid-state Raman Laser

In recent years,research focus on laser has shifted to dual-wavelength laser output,with the widespread application of dual-wavelength laser in precision metrology,information technology,medical diagnosis,and spectral.Orthogonally polarized dual-wavelength Raman laser can be separated easily,and compared to the fundamental laser,it possesses the advantages of better beam quality,narrower pulse width and spectral linewidth.Nd:YLF crystal has two orthogonally-polarized emission peaks with comparable emission cross sections,high-energy storage capability and relatively weak thermal lens effect.Owing to these properties,it has been recognized as a suitable gain medium for generating orthogonally-polarized dual-wavelength laser.In this paper,Nd:YLF crystal is used as the laser gain medium to produce 1047.4 nm and 1053.4 nm dual-wavelength fundamental lasers with orthogonal polarizations,and the risk of thermal cracking of Nd:YLF crystal is reduced by appropriately increasing the pump spot.By using the intracavity Raman frequency shift in BaWO4 crystal,orthogonally-polarized dual-wavelength Raman lasers at 1159.9 nm and 1167.1 nm are achieved with high peak power,and the output characteristics of dual-wavelength Raman laser are studied in detail.The specific research contents are as follows:1.Firstly,the laser characteristics of Nd:YLF crystals are studied theoretically in detail.Secondly,the focal length of thermal lens in Nd:YLF crystal is calculated,and the influence of pump spot size on thermal lens effect is analyzed.Finally,the design principle of Raman laser resonator is studied theoretically.The results show that increasing the pump spot can effectively alleviate the thermal lens effect of the crystal and reduce the risk of thermal fracture.2.By using Nd:YLF crystal as laser medium and acousto-optic Q-switching technology,orthogonally-polarized dual-wavelength fundamental lasers at 1047.4 nm and 1053.4 nm are obtained.The effects of repetition frequency,curvature radius of output mirror,crystal specifications and pump wavelength on the output performance of dual-wavelength fundamental lasers are systematically studied.Under the total incident pump power of 32.7 W and the pulse repetition rate of 30 kHz,a maximum dual-wavelength fundamental output power of 13.4 W is obtained.The corresponding total optical conversion efficiency is 41%.For 1047.4 nm and 1053.4 nm fundamental lasers,the maximum average output powers are 7.6 W and 5.8 W,respectively.The pulse widths are 119.5 ns and 187.0 ns,and the corresponding peak powers are 2.12 kW and 1.03 kW,respectively.3.Using Nd:YLF crystal as the laser medium and BaWO4 crystal as the Raman medium,orthogonally polarized dual-wavelength Raman lasers at 1159.9 nm and 1167.1 nm are realized.The effects of repetition frequency,curvature radius of output mirror and pump spot size on the output performance of dual-wavelength Raman laser are systematically studied.Under the total incident pump power of 40 W and the pulse repetition rate of 5 kHz,a maximum dual-wavelength Raman output power of 2.67 W is obtained.The corresponding total optical conversion efficiency is 6.7%.For 1159.9 nm and 1167.1 nm Raman lasers,the maximum average output powers are 1.31 W and 1.36 W,respectively.The narrowest pulse widths are 1.43 ns and 1.45 ns,and the corresponding peak powers are as high as 183.2 kW and 187.6 kW,respectively.The results show that Nd:YLF/BaWO4 is a promising crystal combination for realizing orthogonally-polarized dual-wavelength Raman laser.