Improvement to beam quality of optically pumped terahertz gas lasers with hole-coupling resonators

摘要

The hole-coupling method, which is commonly used in the optically pumped THz gas laser, will reduce the beam quality due to the hard-edge diffraction. It is shown that by optimizing the parameters of the resonator a diffraction-limited output beam can be obtained. A method is proposed for the selection of a higher order waveguide mode, whose first zero point along the radial direction coincides with the edge of the output hole coupler and the effect of hard edge diffraction is depressed. Measurements of beam quality are taken on an experimental prototype whose optical setup is designed by this method. A quasi-Gaussian beam output is obtained, and the beam quality M2 factor is about 1.15