Liang Miao

Tunable high-efficient pulsed NH3 terahertz lasers

Experimental studies on a tunable efficient high-efficient pulsed NH3 terahertz (THz) lasers pumped by TEA CO2 lasers are presented. When NH3 is pumped by the different lines with the CO2 lasers, the generation of different terahertz radiations is discussed. The lines of the CO2 lasers are 9R(08), 9P(20), 10R(14), 10R(08), and 10R(06). To improve THz laser energy and photon conversion efficiency, different higher power of the CO2 laser can effectively improve THz laser energy and photon conversion efficiency. When the 9P(20) CO2 lasers with 9.68 J and 4.12 J pump NH3, the corresponding energy conversion efficiencies are 0.28% and 0.19%, increasing by a factor of about 1.5. The generation of terahertz radiations with energy as high as 27.29 mJ and 7.73 mJ are obtained, respectively, increasing by a factor of about 3.5. Meanwhile, for 10R(14) line, the energy conversion efficiencies increase to 8.5 times and the energy of THz lasers increase to 32 times.

An efficient optically pumped terahertz laser without metal-mesh mirrors

The efficiency of a simply designed optically pumped terahertz laser is studied experimentally. The terahertz laser cavity only consists of a quartz glass tube, an antireflection-coated Ge window and a SiO2 window. The Ge crystal acts as the high-reflectivity mirror of terahertz radiation and the input coupler of pump laser instead of complicated metal-mesh mirrors. The Ge crystal is near 3 mm thick, whose exact thickness is designed according to etalon effects to maximize terahertz reflectivity. NH3 gas is filled in the cavity as the active medium and pumped by a TEA CO2 laser. As high as 25.9 mJ terahertz radiation at the wavelength of 151.5 μm is extracted from 1.76 J pump energy. The corresponding photon conversion efficiency of this terahertz laser reaches 41.5%. A 4.7-mm-thick GaAs crystal and a 6-mm-thick ZnSe crystal are also chosen to be the input coupler. The experimental results show that the efficiency of the Ge window is 54% and 66% higher than that of the GaAs and ZnSe windows, respectively. The reason of the higher efficiency of the Ge window is demonstrated experimentally and theoretically in this paper.

Evolution of Shock Wave in TEA gas laser

The evolution of shock wave generated by discharge in laser chamber is one of the key factors which affect laser beam quality, discharge stability, and repetition rate of TEA gas laser. In this paper, Mach-Zehnder interferometer is applied to observe both the longitudinal and transversal shock waves between electrodes as well as the acoustic waves originated by preionization in the discharge pumping zone of TEA gas laser. By changing the discharge voltage, gas pressure and gas composition concentration, the developing processes in different conditions are compared and analyzed. It is observed that the shock waves originating from cathode is different from the anodes ones even in the symmetric electrode construction. And the carbon dioxide concentration in helium-buffered working gas can affect the speed of the wave obviously. However, the increasing trend of shock wave speed, when increasing discharge voltage or reducing discharge gas pressure, is inconspicuous.