Research On Tunable Mid-infrared Acetylene Gas Laser Based On Hollow Core Fiber

The wavelengths of mid-infrared lasers coincide with fundamental rotational-vibrational transitions in many molecules,which play a significant role in a variety of potential applications such as defense,medicine and atmosphere communications.At present,fibers doped with rare earth ions are mainly used to generate mid-infrared lasers by the energy level transition of rare earth ions,but the output power is limited by the nonlinear and thermal effects.Mid-infrared fiber gas lasers based on hollow-core fibers combine the advantages of both fiber lasers and gas lasers,which have attained enormous attentions in recent years.When pumped by a modulated,tunable,narrow-linewidth,3.1-3.2 ?m tunable diode laser,laser emission is generated in negative curvature hollow-core fibers filled with low pressure acetylene.The primary contents and results are listed as follows:1.The research background of mid-infrared fiber lasers is demonstrated.The development history and current research states of hollow-core fibers and mid-infrared fiber gas lasers are introduced.The emergence of hollow-core fibers provides a solution to various limitations in the development of mid-infrared fiber lasers.2.Theoretical analysis of acetylene gas laser based on hollow-core fiber is carried out.The theory of vibrational-rotational energy level transition of acetylene molecules is introduced.The absorption characteristics of acetylene molecules,such as absorption intensity distribution,absorption line type and broadening,are expounded.Specifically,the energy level transition process of tunable acetylene-filled fiber gas laser is introduced.On this basis,a four-level system is established and the rate equation is given.3.The tunable 3 ?m acetylene-filled fiber gas laser source is experimentally studied.A tunable narrow-linewidth 1.5 ?m pump source was built and the spectrum,linewidth,pulse and spot characteristics of the pump source are analyzed.The mid-infrared laser with tuning range from 3090 to 3203 nm is obtained and the power,spectrum and spot characteristics of the output laser are analyzed.We get a maximum CW laser power of ?0.77 W by P(15)pump transition at 1.5 mbar gas pressure with a power conversion efficiency of ?13%,and a maximum laser pulse average power of ?0.3 W(?0.6 ?J pulse energy)by P(9)pump transition at 0.9 mbar gas pressure with a power conversion efficiency of ?16%.4.The preliminary experimental research of tunable 3 ?m acetylene-filled fiber gas laser source based on all-fiber structure is carried out.The single mode fiber is tapered,then inserted into the core of hollow-core fiber to form all-fiber structure.We get a maximum laser pulse average power of 125 m W(250 nJ pulse energy)by P(11)and P(13)pump transitions with a stable slope efficiency of ?21%,and a maximum CW laser power of 185 mW by P(15)and P(17)pump transitions with a power conversion efficiency of ?14%.