Photothermal sensing of nanoscale targets

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Abstract
The further development of a photothermal (PT) method for the sensing of nanoscale absorbing targets is presented. This method is based on the irradiation of nanotargets with a short laser pulse and time-resolved PT visualization of laser-induced thermal effects around targets. It is accomplished with second probe beam that senses the target with adjustable time delay after the pump laser pulse. It is shown that an analysis of diffraction limited PT images at a different time delay after a laser pulse can yield information on target size. The practical capability of this approach is demonstrated for visualization of nanoscale gold particles with a tunable parametric pulse laser-OPO (420–570 nm, 0.1–100 μJ, 8 ns width), as a pump laser and Raman-shifter (639 nm, 13 ns width), as a probe laser with a tunable delay of the probe pulse relative to the pump pulse in the range of 0–5000 ns.