Recently we published a paper in Applied Physics B describing our research into the propagation of mid-infrared laser light through hollow silica waveguides. The laser that we were using is a mid-infrared (7.8 μm) quantum cascade laser that is housed in a research platform based on a Cascade Technologies laser spectroscopy system. Hollow silica waveguides are narrow tubes made of silica which are internally coated with silver to allow infrared light to be guided along them. Their typical inner bore diameters range from about 300 μm to 1 mm and have lengths of up to 5 m. They are typically used for accurate guiding very high powered infrared laser beams, such as from CO2 lasers, for precise cutting applications, e.g. in surgery or in industrial machining. Our interest in them lies in the development of spectroscopic gas cells with very low volume and fast response times.
The paper featured in the Applied Physics B special issue covering the FLAIR 2014 conference. It modelling of the coupling coefficients using the overlap integral and validation of the modelling through the use of a thermal imaging camera to monitor the laser output from the waveguide. The results were quantitatively compared by using Fourier transform techniques to analyse the spatial frequency content of the observed speckle patterns. This was done to determine the most effective launch characteristics for different waveguides using our laser.
The paper is open access and can be freely downloaded -
Quantum cascade laser light propagation through hollow silica waveguides
D Francis, J Hodgkinson, B Livingstone* and R P Tatam
Applied Physics B 119(1), 75-86 (2015) - Open Access
*Cascade Technologies Ltd, Stirling, UK,