RESUMO
Infrared vibrational nano-spectroscopy based on scattering scanning near-field optical microscopy (s-SNOM) provides intrinsic chemical specificity with nanometer spatial resolution. Here we use incoherent infrared radiation from a 1400 K thermal blackbody emitter for broadband infrared (IR) nano-spectroscopy. With optimized interferometric heterodyne signal amplification we achieve few-monolayer sensitivity in phonon polariton spectroscopy and attomolar molecular vibrational spectroscopy. Near-field localization and nanoscale spatial resolution is demonstrated in imaging flakes of hexagonal boron nitride (hBN) and determination of its phonon polariton dispersion relation. The signal-to-noise ratio calculations and analysis for different samples and illumination sources provide a reference for irradiance requirements and the attainable near-field signal levels in s-SNOM in general. The use of a thermal emitter as an IR source thus opens s-SNOM for routine chemical FTIR nano-spectroscopy.
RESUMO
It is common practice to work in the approximation that beam-like radiation fields are polarized transverse to the propagation axis. However, even in the paraxial approximation, this fails to correctly describe beam polarization and propagation characteristics. We present here the paraxial Maxwell's equations for beams having cylindrical polarization, which describe the full vector structure of these beams in the paraxial regime. The effect that these relations have on the polarization and propagation of cylindrically polarized Laguerre-Gauss and Bessel-Gauss beams is subsequently explored.