Wavelength stabilisation for high power CO2 slab waveguide lasers using waveguide surface patterning

Abstract

RF excited CO2 slab waveguide lasers are now developed as compact, highly efficient, cost-effective high power laser sources, suitable for a large number of uses. However a major problem remains in that the output power, wavelength and beam shape are unstable in time, leading to restrictions in their use in high precision and wavelength dependent work. A new method of wavelength control has been explored, using 2-D periodic patterns machined directly onto the waveguide surface of one of these lasers. These grating structures have been produced using a laser micro-machining technique which has been developed to allow for accurate and repeatable feature periodicity, along with fast prototyping. Several geometries of gratings, both one and two dimensional, have been machined from a number of materials compatible with IR hollow waveguide use, with feature spacings ranging from 80-150 um. Sensitive techniques developed to measure the wavelength dependent transmission of these waveguides out with a laser cavity, have shown a 2-3% loss selectivity using 50mm long patterns. The inclusion of the two dimensional grating in the unstable resonator of an industrial slab laser device is shown to stabilise the output wavelength to the 10.59 um transition and maintain a constant spatial mode.