363 research outputs found
The low-temperature infrared optical functions of SrTIO3 determined by reflectance spectroscopy and spectroscopic ellipsometry
Mid-infrared frequency comb spanning an octave based on an Er fiber laser and difference-frequency generation
We describe a coherent mid-infrared continuum source with 700 cm-1 usable
bandwidth, readily tuned within 600 - 2500 cm-1 (4 - 17 \mum) and thus covering
much of the infrared "fingerprint" molecular vibration region. It is based on
nonlinear frequency conversion in GaSe using a compact commercial 100-fs-pulsed
Er fiber laser system providing two amplified near-infrared beams, one of them
broadened by a nonlinear optical fiber. The resulting collimated mid-infrared
continuum beam of 1 mW quasi-cw power represents a coherent infrared frequency
comb with zero carrier-envelope phase, containing about 500,000 modes that are
exact multiples of the pulse repetition rate of 40 MHz. The beam's
diffraction-limited performance enables long-distance spectroscopic probing as
well as maximal focusability for classical and ultraresolving near-field
microscopies. Applications are foreseen also in studies of transient chemical
phenomena even at ultrafast pump-probe scale, and in high-resolution gas
spectroscopy for e.g. breath analysis.Comment: 8 pages, 2 figures revised version, added reference
Interferometric and Schlieren Measurements of the Electron Density in Arc Plasmas Using IR Radiation from a CO2 Laser
Nanoscale imaging of the electronic and structural transitions in vanadium dioxide
We investigate the electronic and structural changes at the nanoscale in
vanadium dioxide (VO2) in the vicinity of its thermally driven phase
transition. Both electronic and structural changes exhibit phase coexistence
leading to percolation. In addition, we observe a dichotomy between the local
electronic and structural transitions. Nanoscale x-ray diffraction reveals
local, non-monotonic switching of the lattice structure, a phenomenon that is
not seen in the electronic insulator-to-metal transition mapped by near-field
infrared microscopy.Comment: 23 pages including 7 figure
Nanoscale layering of antiferromagnetic and superconducting phases in Rb2Fe4Se5
We studied phase separation in a single-crystalline antiferromagnetic
superconductor Rb2Fe4Se5 (RFS) using a combination of scattering-type scanning
near-field optical microscopy (s-SNOM) and low-energy muon spin rotation
(LE-\mu SR). We demonstrate that the antiferromagnetic and superconducting
phases segregate into nanometer-thick layers perpendicular to the iron-selenide
planes, while the characteristic in-plane size of the metallic domains reaches
10 \mu m. By means of LE-\mu SR we further show that in a 40-nm thick surface
layer the ordered antiferromagnetic moment is drastically reduced, while the
volume fraction of the paramagnetic phase is significantly enhanced over its
bulk value. Self-organization into a quasiregular heterostructure indicates an
intimate connection between the modulated superconducting and antiferromagnetic
phases.Comment: 5 pages, 2 figures. Updated version published in Phys. Rev. Lett. on
5 July 201
Subdiffractional focusing and guiding of polaritonic rays in a natural hyperbolic material
Uniaxial materials whose axial and tangential permittivities have opposite
signs are referred to as indefinite or hyperbolic media. In such materials
light propagation is unusual, leading to novel and often non-intuitive optical
phenomena. Here we report infrared nano-imaging experiments demonstrating that
crystals of hexagonal boron nitride (hBN), a natural mid-infrared hyperbolic
material, can act as a "hyper-focusing lens" and as a multi-mode waveguide. The
lensing is manifested by subdiffractional focusing of phonon-polaritons
launched by metallic disks underneath the hBN crystal. The waveguiding is
revealed through the modal analysis of the periodic patterns observed around
such launchers and near the sample edges. Our work opens new opportunities for
anisotropic layered insulators in infrared nanophotonics complementing and
potentially surpassing concurrent artificial hyperbolic materials with lower
losses and higher optical localization.Comment: 25 pages, 5 figure
Label-free infrared spectroscopy and imaging of single phospholipid bilayers with nanoscale resolution
Mid-infrared
absorption spectroscopy has been used extensively
to study the molecular properties of cell membranes and model systems.
Most of these studies have been carried out on macroscopic samples
or on samples a few micrometers in size, due to constraints on sensitivity
and spatial resolution with conventional instruments that rely on
far-field optics. Properties of membranes on the scale of nanometers,
such as in-plane heterogeneity, have to date eluded investigation
by this technique. In the present work, we demonstrate the capability
to study single bilayers of phospholipids with near-field mid-infrared
spectroscopy and imaging and achieve a spatial resolution of at least
40 nm, corresponding to a sample size of the order of a thousand molecules.
The quality of the data and the observed spectral features are consistent
with those reported from measurements of macroscopic samples and allow
detailed analysis of molecular properties, including orientation and
ordering of phospholipids. The work opens the way to the nanoscale
characterization of the biological membranes for which phospholipid
bilayers serve as a model
Transmission of light through periodic arrays of square holes: From a metallic wire mesh to an array of tiny holes
J. Bravo-Abad, L. Martín-Moreno, F. J. García-Vidal, Euan Hendry, and J. Gómez Rivas, Physical Review B, Vol. 76, article 241102(R) (2007). "Copyright © 2007 by the American Physical Society."A complete landscape is presented of the electromagnetic coupling between square holes forming a two-dimensional periodic array in a metallic film. By combining both experimental and theoretical results along with a first-principles Fano model, we study the crossover between the physics of metallic wire meshes (when holes occupy most of the unit cell) and the phenomenon of extraordinary optical transmission, which appears when the size of the holes is very small in comparison with the period of the array
Resolution and enhancement in nanoantenna-based fluorescence microscopy
Single gold nanoparticles can act as nanoantennas for enhancing the
fluorescence of emitters in their near-fields. Here we present experimental and
theoretical studies of scanning antenna-based fluorescence microscopy as a
function of the diameter of the gold nanoparticle. We examine the interplay
between fluorescence enhancement and spatial resolution and discuss the
requirements for deciphering single molecules in a dense sample. Resolutions
better than 20 nm and fluorescence enhancement up to 30 times are demonstrated
experimentally. By accounting for the tip shaft and the sample interface in
finite-difference time-domain calculations, we explain why the measured
fluorescence enhancements are higher in the presence of an interface than the
values predicted for a homogeneous environment.Comment: 10 pages, 3 figures. accepted for publication in Nano Letter
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