Corneal damage thresholds for multiple-pulse exposures to 2.02 μm radiation from a Tm:YAG laser

Corneal epithelial damage thresholds were determined for exposures to sequences of pulses from a Tm:YAG laser (wavelength 2.02 μm). Pulse repetition frequencies were 1, 10, 20, and 100 Hz and individual pulse durations were 0.300 sec at 1 Hz, 0.025 sec at 10 and 20 Hz, and 0.005 sec at 100 Hz. Threshold damage is correlated by an empirical power law of the from I_th = CN^-α in which I_th is the threshold irradiance and N is the number of pulses. The constant C differs depending on the pulse repetition frequency and individual pulse duration. The exponent α varies between 0.22 and 0.29. For some exposure conditions the empirical power law underestimates the damage threshold for small numbers of pulses.