Substrate-enhanced infrared near-field spectroscopy.

We study the amplitude and phase signals detected in infrared scattering-type near field optical microscopy (s-SNOM) when probing a thin sample layer on a substrate. We theoretically describe this situation by solving the electromagnetic scattering of a dipole near a planar sample consisting of a substrate covered by thin layers. We perform calculations to describe the effect of both weakly (Si and SiO(2)) and strongly (Au) reflecting substrates on the spectral s-SNOM signal of a thin PMMA layer.

Spectroscopic near-field microscopy using frequency combs in the mid-infrared.

We introduce a new concept of spectroscopic near-field optical microscopy that records broad infrared spectra at each pixel during scanning. Two coherent beams with harmonic frequency-comb spectra are employed, one for illuminating the scanning tip, the other as reference for multi-heterodyne detection of the scattered light. Our implementation yields 200 cm(-1) wide amplitude and phase spectra centered at 950 cm(-1) (this band can be tuned between 700 and 1400 cm(-1)).

Infrared spectroscopic mapping of single nanoparticles and viruses at nanoscale resolution.

We demonstrate that scattering near-field microscopy (s-SNOM) can determine infrared "fingerprint" spectra of individual poly(methyl methacrylate) nanobeads and viruses as small as 18 nm. Amplitude and phase spectra are found surprisingly strong, even at a probed volume of only 10(-20) l, and robust in regard to particle size and substrate. This makes infrared spectroscopic s-SNOM a versatile tool for chemical and-in the case of protein-secondary-structure identification.

Frequency-comb infrared spectrometer for rapid, remote chemical sensing.

We demonstrate real-time recording of chemical vapor fluc-tuations from 22m away with a fast Fourier-transform infrared (FTIR) spectrometer that uses a laser-like infrared probing beam generated from two 10-fs Ti:sapphire lasers. The FTIR's broad 9-12 microm spectrum in the "molecular fingerprint" region is dispersed by fast heterodyne self-scanning, enabling spectra at 2cm-1 resolution to be recorded in 70 micros snapshots. We achieve continuous acquisition at a rate of 950 IR spectra per second by actively manipulating the repetition rate of one laser.