HEATING BY ABSORPTION IN THE FOCUS OF AN OBJECTIVE LENS

We derive an integral solution for the local heating of a linearly abs orbing, uniform medium exposed to strongly focused light. Numerical re sults for local heating under typical multiphoton microscopy and optic al trapping conditions are presented for various aperture angles. In c ontrast with common Gaussian beam approximations, our model employs th e focal-intensity distribution as described by the point spread functi on of the lens. In this way, the model also accounts for axial heat tr ansportation, which results in a lower prediction for the temperature increase. For an aperture of 1.2 (water immersion), irradiation with 1 00 mW of 850-nm light for 1 a increases the local temperature of water by 0.2 K. Heating of water by linear absorption can be ruled out as a limiting factor in standard multiphoton-excitation microscopy. (C) 19 98 Optical Society of America.