Mid-infrared laser-induced superheating of water and is quantification by an optical temperature probe

Free-running thulium laser pulses (Cr:Tm:YAG, λ = 2.01 μm, t_p = 300 μs) were applied to a purified, degassed water sample and the resulting temperature rise was investigated by an optical temperature probe. The probe detected water reflectance index changes with temperature and also the onset of vaporization, which was found to occur in a superheat regime, at approximately 230°C. The experimental data were compared with theoretical temperature calculations, and deviations of less than 20°C were stated. The best agreement between theory and experiment was found for temperatures below 180°C, defining by this the method's high accuracy limit. In conclusion, both the optical temperature probe and the presented calculations can help to improve dosimetry in pulsed IR laser applications by precise temperature measurement and prediction.