Ultrabroadband Nanospectroscopy with a Laser-Driven Plasma Source

Abstract

Scattering-type scanning near-field optical microscopy (s-SNOM) enables infrared spectroscopy at 10− 20 nm spatial resolution through elastic light scattering. Coupled with an infrared light source, s-SNOM characterizes chemical compositions or probes nanoscale photonic phenomena on length scales 2 orders of magnitude below the diffraction limit. However, widespread use of s-SNOM as an analytical standard tool has been restrained to a large extent by the lack of a bright and affordable broadband light source.Here we present a turnkey thermal emitter based on a laserdriven plasma that offers incoherent radiation of a broader bandwidth (>1000 cm −1 ) and ∼40-fold higher brilliance than previous blackbody radiators in addition to a compact size and at a fraction of the cost of alternative coherent laser systems or synchrotrons. We demonstrate a nearly 1 order of magnitude increase in signal-to-noise in near-field spectra compared to existing incoherent emitters, which allows probing of not only inorganic materials and polaritonic systems but also various commonly used polymers despite their weak near-field optical response. The latter important representative of soft matter was previously inaccessible by table-top thermal radiators. s-SNOM combined with the laser-driven plasma will provide a widely accessible platform for infrared nanospectroscopy.

Subsurface chemical nanoidentification by nano-FTIR spectroscopy

“…Our model (Eqs. (4) and (6)) shows that the spectral behavior of nano-FTIR signals essentially follows the spectral behavior of β, as neither the exponent j nor the geometry factors f 0 and f 1 in Eq. (4) lead to spectral peak shifts.…”

“…The quantitative differences between Arg βðωÞ and φ 3 (ω) can be explained by signal demodulation in nano-FTIR, which has not been considered so far in our analysis of β. Eqs. (4) and (6) imply that signal demodulation (described by the Fourier componentsF n ) acts on the CWF, w(q, H), which depends on the modulated tip-sample distance H. It is well known 23,29,30 that s-SNOM imaging at higher demodulation orders improves the lateral spatial resolution and reduces the probing depths, indicating that near fields of larger momenta are probed. This corresponds to near-field probing at higher momenta q for increasing n, and explains the reduction of the nano-FTIR spectral peak shifts for surface layer and an increase for subsurface layers (compared with bulk) observed in Fig.…”

“…cattering-type scanning near-field optical microscopy (s-SNOM) 1 is a scanning probe microscopy technique that offers nanoscale-resolved optical imaging of a wide range of samples, including polymers [2][3][4] , biological materials [5][6][7][8] , semiconductors [9][10][11] , conductors 12 and insulators 13 . In s-SNOM, monochromatic electromagnetic radiation of the visible, infrared, or terahertz spectral range is focussed onto the tip of a standard, metallized atomic force microscope (AFM) probe.…”

Nanoimaging and Nanospectroscopy of Polaritons with Time Resolved s‐SNOM

“…This is similar to the setup of Fourier‐transform infrared spectroscopy (FTIR). With a broadband probe light source, such as synchrotron light, high temperature plasma light source, or laser driven plasma, such setup, so‐called nano‐FTIR, can measure IR spectra with a spatial resolution of ≈20 nm . The technique has produced flourish results in phase transition materials, polariton dispersion, catalytic chemistry, biology, and geoscience, among other fields …”

Rapid Infrared Spectroscopic Nanoimaging with nano-FTIR Holography

“…The implementation of infrared broadband sources in s-SNOM enabled Fourier transform infrared nanospectroscopy (nano-FTIR), a derivate of s-SNOM that overcomes the diffraction-limited spatial resolution of conventional FTIR spectroscopy. In nano-FTIR, the AFM tip is illuminated with IR broadband radiation from thermal sources [22][23][24][25][26], difference frequency generation (DFG) [4,[27][28][29][30] or synchrotrons covering the entire mid-infrared range [31][32][33][34]. The tip-scattered light is analyzed with an asymmetric Fourier transform spectrometer, yielding IR amplitude and phase spectra with the spatial resolution of s-SNOM.…”