The application of the mid-infrared spectral region in medical surgery: Chalcogenide glass optical fibre for 10.6 μm laser transmission

Infrared-transmitting glass optical fibres are being developed for intended applications in medicine and industry as part of a laser delivery system, giving more flexibility and accuracy of positioning of the laser beam for the User. Chalcogenide glass optical fibre is being designed to transmit light at 10.6 µm, to coincide with the wavelength of the output light from the CO ₂ laser. In medicine, ablative surgery performed using the CO ₂ laser causes less damage to surrounding tissue than when using shorter wavelength laser sources. The effect of composition of chalcogenide glasses on optical absorption, across the wavelength range 3 µm to > 15 µm, has been investigated using Fourier transform infrared (FTIR) spectroscopy, for a range of binary, ternary and quaternary glasses, in the form of small bulk glass specimens. Glasses containing germanium tended to exhibit higher glass transformation temperatures but a shorter wavelength multiphonon edge. The optical loss of fibre samples has been measured at 10.6 µm using a high power CO₂ laser source and employing the fibre cut-back method. As₂Se and Te₃₀As₂₀Se₅₀ fibres (both unclad) exhibited 7.2, and 2.3, dBm^-1, respectively. Ge ₁₇As₁₈Se₆₅ / Ge₁₇As ₁₈Se₆₂S₃ core/clad. fibre exhibited an optical loss of 10.3 dBm^-1. After the optical loss measurements, fibres were imaged using scanning electron microscopy and it was found that the high power CO₂ laser caused damage to the launch end of some fibres. In particular, at the launch-end of Te-As-Se fibres the glass appeared to have undergone partial melting and possibly also suffered some vaporisation.