Time-resolved observation of thermal and mechanical effects in tissue models induced by short laser pulses from an optical parametric oscillator

摘要

Heat and stress generation in water are investigated after irradiation with single, short pulses (5 ns duration) from an optical parametric oscillator (OPO), using piezoelectric stress detection, an optical pump-probe technique and laser-flash photography. The wavelength dependence of these effects is studied in the near infrared by choosing some wavelengths at the absorption peak between 1900 nm and 2050 nm from the wide tuning range of the OPO (400 nm - 2500 nm). Time-resolved temperature profiles show the relatively slow decay of the heat generated by absorption of a pulse, leading to the possibility of heat accumulation by successive pulses. Relaxation of the thermoelastic stress near a free surface causes cavitation and liquid ejection. This effect can be intensified by vaporization. The observation that the ablative effects of heat and stress are maximized at the absorption peak demonstrates the applicability of the OPO for optimized tissue ablation.