Listening to nanostructures’ absorption with many degrees of freedom: widely tunable photo-acoustic characterization

Photo-acoustic technique is a promising tool for studying materials’ absorption, having applications from characterization of novel nano-devices to biomedical imaging. We show how a photo-acoustic spectroscopy (PAS) set-up can be boosted with new degrees of freedom, overcoming previous limitations such as low power and inability to precisely tune the polarization. We use a widely tunable laser and modulate its output with a tunable mechanical chopper. The input polarization is controlled by a linear polarizer and a quarter-wave plate, and the laser can be focused before impinging on the sample in a closed photo-acoustic cell. We further enrich the set-up with rotational and translational stages. We show the possibility to map the absorption of commercial nanostructured samples both spectrally and spatially, and we comment on PAS limitations. We strongly believe that such PAS set-up can be conventionally used to map absorption of nanostructured materials in a broad wavelength range, with additional control of the polarization, angle of incidence, modulation frequency and beam diameter properties