Investigation On Orthogonally Polarized Dual-wavelength Raman Laser

Orthogonally polarized dual-wavelength laser have significant application in precision measurement,laser interference,holographic technology,differential absorption lidar and coherent terahertz(THz)generation.At present,there are two main ways to generate orthogonally polarized dual-wavelength lasers: one is to use the multiple fluorescent emission lines of the rare-earth-doped anisotropic laser materials.but due to the limitation of the laser medium,the spectral range is mainly focus on the 0.9 ?m,1.0 ?m,1.3 ?m and2.0 ?m spectral regions.Another way is optical parametric oscillation(OPO),but optical parametric oscillation requires strict phase matching,and most nonlinear media work near the damage threshold.Compared with stimulated radiation,stimulated Raman scattering has the advantage of pulse duration shortening and beam clean-up;compared with OPO,it has the advantages of not requiring phase matching and more stable performance.The article is mainly based on Nd:YLF laser crystal and KGW Raman crystal to carry out a series of orthogonal Raman dual-wavelength laser experiments.1.It is the first time to expand the frequency range of orthogonally polarized dualwavelength lasers through cascade stimulated Raman scattering.(1)In order to avoid gain competition,13.7 W@5 k Hz 1047 nm and 1053 nm orthogonally polarized dual-wavelength fundamental lasers were obtained through two separate Nd:YLF crystals,which is nearly 3times higher than similar international lasers.(2)Based on the characteristics of the KGW crystal with different maximum Raman frequency shifts in the orthogonal direction,first,by selecting the Raman crystal to obtain two sets of first-Stokes lasers of 1139 nm,1164 nm and 1156 nm,1146 nm.The average output power is approximately 3.1 W,and the total peak power is approximately 240 k W.(3)By replacing the Raman coupler,two sets of secondorder Stokes lasers of 1248 nm,1300 nm,1291 nm,and 1256 nm were obtained,and the average output powers were 1.9 W and 2.1 W,respectively.The peak powers are 220 k W and 290 k W,which are more than twenty times higher than the previous study.2.The first report of 1.3 ?m band orthogonally polarized dual-wavelength Nd:YLF laser output.(1)Reasonably design the cavity to ensure that the laser output of the two polarization directions work in the thermally stable region.Utilize the characteristics of the similar stimulated emission cross section of the Nd:YLF crystal at the 1.3 ?m band,and adjust the cavity mirror to ensure the power of the two polarization directions is balanced;(2)On this basis,the continuous-wave(CW)output power is 9.2 W and the slope efficiency is 33%.At a pulse repetition frequency(PRF)of 20 k Hz,an average output power of 6.5 W is obtained,which is the highest average output power currently obtained in the 1.3 ?m band for continuous and Q-switched;(3)At the PRF of 1 k Hz.The peak power of 72 k W is obtained.Which is two orders of magnitude higher than similar lasers.3.For the first time,the eye-safe orthogonally polarized dual-wavelength Raman laser is realized.(1)Combined with low quantum depletion pumping technology,the fundamental laser output of the 1.3 ?m band with an average power of 5.1 W was obtained,and its repetition frequency was 5 k Hz;(2)Using the biaxial characteristics of the KGW crystal,the two sets of orthogonally polarized laser outputs at 1470 and 1490 nm,1461 and 1499 nm was obtained.With the average output powers of 2.6 and 2.4 W,respectively,which are close to the current highest average output power.The pulse widths are 5.8 ns and 6.3 ns,and the corresponding peak powers are 89.7 k W and 76.5 k W,which are more than three times higher than similar lasers.