4.5W中红外3.1μm光纤气体激光器

4.5 W 3.1 μm Mid-Infrared Fiber Gas Laser

在突破了高功率泵浦激光高效稳定耦合关键技术的基础上,利用~30 W的窄线宽1.5μm光纤激光放大器泵浦一段~8 m长、充有300 Pa乙炔的空芯光纤,实现了4.5 W的3.1μm波段中红外激光输出,这是目前中红外光纤气体激光器的最高输出功率,对应的光光转换效率(相对于泵浦源功率)约为14%。实验结果表明,光纤气体激光器具备输出高功率中红外激光的潜力。

Objective Fiber gas lasers combine the advantages of fiber lasers and gas lasers,which are potential and effective means to achieve a mid-infrared laser output.The hollow-core fiber(HCF)confines a high-energy-density laser to transmit long distances in the hollow core,which can enhance the laser-gas interaction and reduce the threshold of agas laser.A reasonable design of microstructures makes the silica-based HCF support mid-infrared laser transmission.By filling different kinds of gases as gain media,a3-5μm mid-infrared narrow linewidth fiber laser can be realized in the HCF,based on intrinsic absorption or stimulated Raman scattering of the gas medium.In2011,acetylene was filled into an HCF for the first time to achieve a mid-infrared laser output in the 3.1μm band.Since then,with the development of HCFs,related research has continued to deepen.So far,the highest output power of fiber acetylene lasers is only 1.2 W.Recently,the National University of Defense Technology has made an important progress in the key technology of efficient and stable coupling under high pump power and low gas pressure airtight conditions.By improving the sealing technology,we realize a 4.5 W mid-infrared fiber laser at 3.1μm in an acetylene-filled HCF,corresponding to an optical-to-optical conversion efficiency of 14%,which is the highest output power of such lasers reported at home and abroad.Methods Figure 1 shows the experimental setup of the single-pass fiber acetylene gas laser without a cavity.Thepump source is a tunable narrow linewidth continuous-wave fiber amplifier with a power of up to 50 W,and the tuning band covers the absorption spectrum of acetylene gas.The pump laser is coupled into the HCF through two planoconvex lenses.Both ends of the HCF are hermetically sealed in the gas cells,through which the HCF can be filled into acetylenes and the pressure can be controlled.By improving the sealing technology,the incident power can be effectively increased from ~10 Wto~30 W.The windows placed in the gas cells incline at an angle of 8°to prevent the reflection of back light from destroying the pump source.After the acetylene gas filled in the HCF absorbs the pump laser,the population inversion occurs,and a 3.1μm signal laser is generated.The generated signal laser and the residual pump laser in the HCF propagate through the output window and are separated by a dichroic mirror.The fiber used in the system is a nodeless anti-resonant HCF,and its cross section is shown in the inset in Fig.1.Results and Discussions Pumped by a 1535.39 nm high power fiber amplifier,~3106 nm [P(17)]and~3182 nm [R(15)]signal lasers are realized in the HCF filled with ~300 Pa acetylene [Fig.2(a)].Due to the single-pass structure without a cavity,the signal laser is amplified spontaneous emission.But because the absorption and emission line widths of acetylene molecules are extremely small(on the order of hundreds of MHz),the fiber acetylene gas laser has the characteristic of narrow line width.The P(17)spectral line is generated first.With the increase of pump power,the intensity of R(15)spectral line gradually approaches and slightly exceeds that of the P(17)spectral line.The relative gain relationship of two spectral lines determines the difference in threshold,and the gain saturation characteristic determines that these two spectral lines are equivalent in intensity at high power.Figure 2(b)plots the curve of the signal laser power versus pump power when the output gas cell is filled with 300 Pa acetylene pressure.The maximum power of ~4.5 W at 3.1μm is achieved in the HCF filled with 300 Pa acetylene with a slope efficiency of 14.3%.The inclined windows lead to the output laser to be split into two beams,which can be modified by window coating.The original output of the HCF has good fundamental mode characteristics.Conclusions In summary,we have achieved a 4.5 W mid-infrared laser output at 3.1μm in an acetylene-filled HCF,corresponding to an optical-to-optical conversion efficiency of 14%,which is the currently the maximum power of a fiber gas laser in the mid-infrared region.The experimental results show that fiber gas lasers have the potential to achieve high-power mid-infrared fiber laser outputs.