Temperature dependence of melanosome microcavitation thresholds produced by single nanosecond laser pulses

Thresholds for microcavitation of isolated bovine retinal melanosomes were determined as a function of temperature using single nanosecond laser pulses at 532 nm and 1064 nm. Melanosomes were irradiated using a 1064-nm Qswitched Nd:YAG (doubled for 532-nm irradiation). Time-resolved microscopy was accomplished by varying the delay between the irradiation beam and an illumination beam allowing stroboscopic imaging of microcavitation events. Results indicated a decrease in microcavitation fluence threshold with increasing sample temperature for both 532-nm and 1064-nm single pulse exposures. The nucleation temperature at both wavelengths was extrapolated through the linear relationship between the temperature increases and the decrease in fluence threshold. In addition, absorption coefficients of melanosomes for visible and near-infrared wavelengths were estimated using the calculated nucleation temperatures.