Terahertz and mid-infrared photoexpansion nanospectroscopy

Abstract

We report a method of taking mid-infrared and terahertz spectra on nanoscale using compact mW-level sources, such as quantum cascade lasers, and a standard atomic force microscope (AFM). Light absorption is detected via deflection of an AFM cantilever due to local sample thermal expansion. The spatial resolution is principally determined by the diameter of the high-intensity spot in the vicinity of a sharp metalized AFM tip, and is below 50nm. To enable detection of minute sample expansion, the repetition rate of the laser pulses is moved in resonance with the cantilever mechanical frequency. The technique requires no optical detectors.