Laser self-detection operation of a mid-IR near-field microscope

Self-detection is demonstrated as a simplifying new operation mode of scattering-type near-field optical microscopy (s-SNOM) in the mid infrared (6.2 μm wavelength). The back-scattered light from a tapping AFM tip is fed back into the quantum cascade laser used as illumination source such that recording of the laser voltage, at harmonics of the tapping frequency, generates amplitude and phase near-field images. This method is validated in a dual setup that simultaneously allows the usual homodyne operation mode which requires a detector and an asymmetric Michelson interferometer. [1] Detector-less self-detection-mode s-SNOMs should work also with semiconductor lasers in the visible and near-infrared, and most importantly, also in the THz region[2] which lacks fast, sensitive detectors.