Photothermal heterodyne imaging of individual metallic nanoparticles: Theory versus experiment

We present the theoretical and detailed experimental characterizations of photothermal heterodyne imaging. An analytical expression of the photothermal heterodyne signal is derived using the theory of light scattering from a fluctuating medium. The amplitudes of the signals detected in the backward and forward configurations are compared and their frequency dependences are studied. The application of the photothermal heterodyne detection technique to the absorption spectroscopy of individual gold nanoparticles is discussed and the detection of small individual silver nanoparticles is demonstrated.