We explore the performance of a scanning near‐field infrared microscope, which works by scattering tightly focused CO2 laser radiation (λ = 10 μm) from the apex of a metallized atomic force ...microscope tip. The infrared images of test samples prove a spatial resolution of 30 nm and are free of topographical and inertial artefacts, thus they should be of great interest for practical applications. We also observe that the infrared contrast vanishes when the input beam polarization is orthogonal to the tip axis, in accordance with theoretical expectations for a mechanism of longitudinal field interaction.
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 andin the case of proteinsecondary-structure identification.
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. Potential applications include video-rate chemical imaging and transient spectroscopy of e.g. gas plumes, flames and plasmas, and generally non-repetitive phenomena such as those found in protein folding dynamics and pulsed magnetic fields research.
Quite unexpectedly, THz and infraredspectroscopy has now a real chance to solveproblems in the nanosciences. This rests ona new microscope technique that overcomesthe Abbe diffraction limit, by using ...thenear field of a metal antenna in closeproximity to a scanned sample surface. HereI briefly summarize present activities inthe microwave, mid-infrared and visiblespectral ranges. It seems straightforwardand highly desirable to fill the existinggap between about 20 GHz and 20 THz, andattain spatial resolution of 10 nm andbelow also in this important part of theelectromagnetic spectrum.
`Apertureless' probe tips have a much higher resolution potential compared to the traditional aperture tips of scanning near-field optical microscopes (SNOM), yet when illuminated by a laser focus a ...large amount of unwanted background scattering occurs both at the probe shaft and at the sample. Here we study in detail how this background can be suppressed by dithering the probe–sample distance, and thereby demonstrate how to enhance the optical near-field contrasts. We find from theory that the coupling of probe dipole and its image in the sample causes a steep increase of scattering cross-sections at small probe–sample distances. This strongly non-linear behavior produces higher harmonics when modulating the distance. Demodulation at higher harmonics, therefore, enables an effective probe tip `sharpening' and improves both resolution and image contrast. This effect is experimentally confirmed by imaging purely dielectric contrast of a topographically flat pn
+-nanostructured semiconductor, realizing
λ/100 resolution at 10 μm infrared wavelength.
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