Upon illumination of the nanojunction formed between an atomically sharp tip and the sample, both the tip and specimen experience heating, followed by thermal expansion. Whereas sample expansion forms the basis of photothermal infrared (PTIR) microscopy, the effect of tip expansion remains unclear. In this contribution we model and measure the tip heating and expansion effect and quantify its contribution under conditions typical for light-based scan probe microscopy.
Surface-enhanced analogues of coherent Raman scattering (CRS) methods are promising candidates to probe molecular vibrations at much faster rates than what can be achieved with surface-enhanced Raman scattering (SERS). Thus far, experimental challenges have prevented surface-enhanced versions of CRS from growing into a practical tool. One of the major hurdles is the fragility of metallic antenna systems that support surface plasmons when illuminated with ultrafast pulses, causing photo-induced damage to the enhancement structures and lowering the repeatability of surface-enhanced nonlinear Raman measurements. In this contribution we discuss several implementations of surface-enhanced coherent anti-Stokes Raman scattering (SE-CARS) that avoid the use of metallic structures and use dielectric antenna systems instead.
The chirality of electromagnetic beams is a property relevant to various nanophotonic applications, yet this property is challenging to characterize at the nanoscale. We have found that electromagnetic beam chirality can be probed through the optical force exerted on a cantilevered, chiral tip. We demonstrate that the differential force, i.e. the difference in the force induced by a focused beam and an auxiliary beam of opposite handedness, exhibits a direct correspondence to the beam’s time-averaged helicity density. Measurement of the differential force yields spatially resolved maps of the helicity density of tightly focused beams with sub-diffraction limited resolution.
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