报道了一种基于空芯光纤的光泵浦中红外HBr气体激光器。用一台可调谐的窄线宽2 μm连续波掺铥光纤放大器泵浦一段充低压HBr气体的4.4 m反共振空芯光纤,通过将种子激光的波长精确调谐到HBr(同位素H ⁷⁹Br)气体R(2)吸收线1971.7 nm附近,使得处于振动基态 v0的H ⁷⁹Br分子跃迁至振动激发态v₂,并在振动态v₂与v₁之间形成粒子数反转,通过跃迁选择定律同时激射出两条谱线R(2)和P(4),波长分别为3977.2 nm和4165.3 nm。当HBr气压为6.2 mbar时,4 μm激光最大输出功率为125 mW,相对于耦合进空芯光纤的泵浦光功率转换效率约为10%。通过进一步改善空芯光纤的传输损耗谱,提高泵浦光耦合效率,可大幅提升激光效率和输出功率,并且利用HBr分子的能级特性,将来有望实现大范围调谐的中红外激光输出。

An optically pumped mid-infrared HBr gas laser based on hollow-core fiber (HCF) is reported. A tunable narrow linewidth 2 μm continuous-wave thulium-doped fiber amplifier is used to pump a 4.4 m anti-resonance hollow-core fiber filled with low-pressure HBr gas. When the seed wavelength is precisely tuned to the R(2) absorption line near 1971.7 nm of hydrogen bromide isotope H ⁷⁹Br, the H ⁷⁹Br molecules in the vibrational ground state v₀ will transit to the vibrational excited-state v₂, then a population inversion will be formed between the vibrational excited states v₂ and v₁. Due to the transition selection rules, two transitions will simultaneously occur by the spectral lines R(2) and P(4), whose wavelengths are 3977.2 nm and 4165.3 nm, respectively. When the HBr pressure is 6.2 mbar, the maximum output power of 4 μm laser is 125 mW, and the optic-to-optic conversion efficiency is about 10% in terms of the pump light coupled into the HCF. By further improving the transmission loss spectrum of the HCF and increasing the coupling efficiency of the pump light, the laser efficiency and output power can be greatly improved, and a wide-range tunable mid-infrared laser emission could be obtained owing to the energy level characteristics of HBr molecules in the future.