Photothermal heterodyne holography of gold nanoparticles.

We report a method based on heterodyne numerical holography associated to photothermal excitation for full field and three-dimensional localisation of metallic nanoparticles. A modulated pump laser (lambda = 532 nm) heats several particles, creating local refractive index changes. This modulation is detected using a probe and a local oscillator beam (lambda = 785 nm), frequency-shifted to create a hologram beating at low frequency. Tens of particles, down to diameters of 10 nm, can be localised simultaneously and selectively in three dimensions with near- diffraction resolution by a numerical reconstruction of a single hologram acquired in 5 s.