Optical nanoscopy of transient states in condensed matter

TL;DR

This paper introduces a novel nano-probe technique using scattering-type scanning near-field optical microscopy (s-SNOM) with sideband-demodulation to track transient states in materials, enabling detailed analysis of ultrafast and slow processes across a broad spectrum.

Contribution

The paper presents a new application of s-SNOM with sideband-demodulation for selectively probing stimuli-induced changes in near-field optical properties of transient states.

Findings

Successfully tracked decay of electron-hole plasma in SiGe films

Demonstrated universal applicability across UV to THz spectral range

Enabled distinction of different contributions to complex phenomena

Abstract

Recently, the fundamental and nanoscale understanding of complex phenomena in materials research and the life sciences, witnessed considerable progress. However, elucidating the underlying mechanisms, governed by entangled degrees of freedom such as lattice, spin, orbit, and charge for solids or conformation, electric potentials, and ligands for proteins, has remained challenging. Techniques that allow for distinguishing between different contributions to these processes are hence urgently required. In this paper we demonstrate the application of scattering-type scanning near-field optical microscopy (s-SNOM) as a novel type of nano-probe for tracking transient states of matter. We introduce a sideband-demodulation technique that allows for probing exclusively the stimuli-induced change of near-field optical properties. We exemplify this development by inspecting the decay of an electron-hole plasma generated in SiGe thin films through near-infrared laser pulses. Our approach can universally be applied to optically track ultrafast/-slow processes over the whole spectral range from UV to THz frequencies.