Visible and near-infrared nanoscale spectroscopy with photo-induced force microscopy

Photo-induced force microscopy (PiFM) uses laser modulation at the atomic force microscope cantilever's typical mechanical resonance frequency, to encode the material near-field response in the probes nanomechanics. While this technique offers the simplicity gained by mechanical detection, it can be challenging for hyperspectral measurements. Modulation in the visible and near-infrared ranges, often involves using acousto-optic modulators that introduce a wavelength-dependent laser steering, detrimental for spectroscopic purposes. Here, we introduce an innovative strategy, based on an electro-optic modulator (EOM), which eliminates the need for realignment, making PiFM a valuable tool for nanoscale spectroscopy in the visible and near-infrared spectra. We test the new EOM-based setup on a WSe₂ sample where we visualize the propagation of polaritonic waveguide modes, which hybridize with the material exciton to form exciton-polaritons. Finally, we extend this EOM-based PiFM setup from standard amplitude-modulation PiFM to polarization-modulation PiFM, paving the way for investigations, at the nanoscale, of linear birefringence and dichroism in the visible and near-infrared ranges.