Enhanced single transverse mode oscillation by an intracavity circular hollow glass waveguide

Abstract

We present in this paper a theoretical and experimental investigation of laser transverse mode control in a stable resonator using a circular hollow glass waveguide (i.e. a capillary) as mode control element. The resonator round trip losses for linearly polarized hybrid hollow glass waveguide eigenmodes, EH 1 m , are calculated and they are compared with those of eigenmodes, TEM 0 m , of a laser resonator using an intracavity circular aperture. Theoretical analysis shows that a capillary resonator has the following two advantages over an aperture adapted resonator: (a) low loss for fundamental transverse mode and at the same time, (b) high degree of mode selection. Thus the use of a capillary in a resonator is expected to enhance the oscillation of the fundamental transverse mode and to quench higher-order modes. The theoretical results are supported by the experiment performed both with a pulsed dye laser and with a Q-switched Nd: YAG laser, as the output powers of the fundamental transverse mode for the liquid and solid lasers are all enhanced due to the replacement of an intracavity pinhole with an intracavity capillary. The experimentally determined optimal waveguide parameters are also in good agreement with our theory.