Research On Compact Optically-pumped Gas Terahertz Laser And Negative-curvature Hollow-core Fiber

Optically-pumped gas terahertz laser(OPTL)is one of the major methods to obtain terahertz(THz)radiation,which has great applications in biomedical,security check,THz radar and other fields.Based on the design of gold-coated quartz waveguide,combined with the designs of pump laser and the THz laser cavity,a compact and high power OPTL is achieved.Meanwhile,THz fiber laser technology is studied,including THz transmission fiber based on negative-curvature hollow-core fiber and optically pumped gas THz fiber laser(OPTFL).The research contents are as follows:1.Using the rate equation theory and a simplified three-level model to anylize the kinetics process of optically-pumped methanol gas THz laser.Meanwhile,A tunable high-performance CW CO₂ laser is built as the pump laser for OPTL,which can provide82 spectral lines and the maximum output power at 9.69?m wavelength is 80 W.A gold-coated quartz waveguide for OPTL oscillator is designed,combining the designs of the input and output coupling mirrors,a compact OPTL system is built.When the pump power is 40 W,the OPTL realizes a maximum output power of 110 m W and the5-minute power stability is within 5%at 2.5 THz frequency.2.To realize the high-performance THz transmission,a negative-curvature hollow-core fiber with elliptical cladding tubes is designed.By investigating the transmission characteristics of hollow-core fiber,a low-loss single-mode THz fiber is proposed.The loss of fundamental mode is 0.45 dB/m and loss of high order mode is 1.88 dB/m.3.In order to compact the OPTL,the OPTFL technology is studied.Combining rate equation theory with the transmission theory of hollow-core fiber,a long-cavity OPTFL based on negative-curvature hollow-core is presented and the factors affecting the energy conversion efficiency of OPTFL are studied.Theoretical calculations show that when the negative-curvature hollow-core fiber with a bending radius of 30 cm,a length of 10 m,a pressure of 250 m Torr,and a pump power of 10 W,the output power of the OPTFL can reach the magnitude of 100 milliwatts.