Photothermal microscopy of nano-objects

The further development of a time-resolved photothermal (PT) method for sensing nano-scale absorbing targets is presented. This method is based on irradiation of nano-targets with a short laser pulse and time-resolved PT visualization of laser-induced thermal effects around targets. It is accomplished with a second probe beam that senses the target with an adjustable time delay after the pump laser pulse. The practical capability of this new approach is demonstrated for visualization of nano-scale gold particles (2-250 rim), liposomes (30-90 nm), Neutral Red (NR) particles (30-500 nm), and polystyrene beads as a calibration tool, with a tunable parametric pulse laser-OPO (420-570 nm, 0.1-300 muJ, 8-ns width) as a pump laser and Raman-Shifter (639 nm, 13 ns width, 10 nJ) as a probe laser with a tunable delay of the probe pulse relative to the pump pulse in the range of 0-5000 ns. The further development of our PT technique is discussed with a focus on visualization of nano-scale absorbing zones during laser-cell interaction.