307 research outputs found
OberflÀchenverstÀrkte Infrarot-Spektroskopie mittels Gold-Nanoantennen
Im Rahmen dieser Arbeit wurden elektrochemisch prĂ€parierte Gold-NanodrĂ€hte und lithographisch hergestellte Gold-Nanostreifen mit Durchmessern von ungefĂ€hr 100nm an der Synchrotronstrahlungsquelle ANKA im Forschungszentrum Karlsruhe hinsichtlich ihrer infrarot optischen Eigenschaften untersucht. UnabhĂ€ngig vom Durchmesser derNanoantennen und deren kristalliner QualitĂ€t wurden antennenartige Plasmonenresonanzengefunden, deren spektrale Eigenschaften von der AntennenlĂ€nge dominiert werden. Ein erhöhter Fernfeld-Extinktionsquerschnitt von Nanoantennen weist auf ihre FĂ€higkeit hin, elektromagnetische Strahlung auf ein nanoskaliges Volumen zu konzentrieren, ein Effekt, den wir uns bei der oberflĂ€chenverstĂ€rkten IR-Spektroskopie (SEIRS) zu Nutze machen. Zur Demonstration der SEIRS wird eine Oktadekanthiol- (ODT) Monolage auf Gold-Nanoantennen adsorbiert. AbhĂ€ngig von der Resonanzfrequenz im VerhĂ€ltnis zu der Adsorbatschwingung (2855 Wellenzahlen und 2927 Wellenzahlen) können VerstĂ€rkungsfaktoren bis zu 500 000 erzielt werden, welche die Spektroskopie von weniger als 100 Attogramm ODT ermöglicht. Im Vergleich zu herkömmlichen oberflĂ€chenverstĂ€rkten Infrarot Absorptions-Techniken eine um zwei GröĂenordnungen höhere VerstĂ€rkung. Resultate aus elektromagnetischen Streusimulationen (boundary element method) verifizieren die experimentell beobachteten asymmetrischen Linienformen der Adsorbatschwingungen, welche durch die Wechselwirkung von plasmonischer und molekularer Anregungen zu Stande kommen. Ein Nachweis, dass die Wechselwirkung elektromagnetischer Natur ist
Addressable metasurfaces for dynamic holography and optical information encryption
We present addressable plasmonic metasurfaces for optical information encryption and holography.</jats:p
Real-Time Tracking of Coherent Oscillations of Electrons in a Nanodevice by Photo-assisted Tunnelling
Coherent collective oscillations of electrons excited in metallic
nanostructures (localized surface plasmons) can confine incident light to
atomic scales and enable strong light-matter interactions, which depend
nonlinearly on the local field. Direct sampling of such collective electron
oscillations in real-time is crucial to performing petahertz scale optical
modulation, control, and readout in a quantum nanodevice. Here, we demonstrate
real-time tracking of collective electron oscillations in an Au bowtie
nanoantenna, by recording photo-assisted tunnelling currents generated by such
oscillations in this quantum nanodevice. The collective electron oscillations
show a noninstantaneous response to the driving laser fields with a decay time
of nearly 10 femtoseconds. The temporal evolution of nonlinear electron
oscillations resulting from the coherent nonlinear optical response of the
nanodevice were also traced in real-time. The contributions of linear and
nonlinear electron oscillations in the generated tunnelling currents in the
nanodevice were precisely determined. A coherent control of electron
oscillations in the nanodevice is illustrated directly in the time domain.
Functioning in ambient conditions, the excitation, coherent control, and
read-out of coherent electron oscillations pave the way toward on-chip
light-wave electronics in quantum nanodevices
Nearly diffraction limited FTIR mapping using an ultrastable broadband femtosecond laser tunable from 1.33 to 8 ”m
Micro-Fourier-transform infrared (FTIR) spectroscopy is a widespread technique that enables broadband measurements of infrared active molecular vibrations at high sensitivity. SiC globars are often applied as light sources in tabletop systems, typically covering a spectral range from about 1 to 20 ”m (10 000 - 500 cmâ1) in FTIR spectrometers. However, measuring sample areas below 40x40 ”m2 requires very long integration times due to their inherently low brilliance. This hampers the detection of ultrasmall samples, such as minute amounts of molecules or single nanoparticles. In this publication we extend the current limits of FTIR spectroscopy in terms of measurable sample areas, detection limit and speed by utilizing a broadband, tabletop laser system with MHz repetition rate and femtosecond pulse duration that covers the spectral region between 1250 - 7520 cmâ1 (1.33 - 8 ”m). We demonstrate mapping of a 150x150 ”m2 sample of 100 nm thick molecule layers at 1430 cmâ1 (7 ”m) with 10x10 ”m2 spatial resolution and a scan speed of 3.5 ”m/sec. Compared to a similar globar measurement an order of magnitude lower noise is achieved, due to an excellent long-term wavelength and power stability, as well as an orders of magnitude higher brilliance
Electrochemically-controlled metasurfaces with high-contrast switching at visible frequencies
Recently in nanophotonics, a rigorous evolution from passive to active
metasurfaces has been witnessed. This advancement not only brings forward
interesting physical phenomena but also elicits opportunities for practical
applications. However, active metasurfaces operating at visible frequencies
often exhibit low performance due to design and fabrication restrictions at the
nanoscale. In this work, we demonstrate electrochemically controlled
metasurfaces with high intensity contrast, fast switching rate, and excellent
reversibility at visible frequencies. We use a conducting polymer, polyaniline
(PANI), that can be locally conjugated on preselected gold nanorods to actively
control the phase profiles of the metasurfaces. The optical responses of the
metasurfaces can be in situ monitored and optimized by controlling the PANI
growth of subwavelength dimension during the electrochemical process. We
showcase electrochemically controlled anomalous transmission and holography
with good switching performance. Such electrochemically powered optical
metasurfaces lay a solid basis to develop metasurface devices for real-world
optical applications
Defect-induced activation of symmetry forbidden infrared resonances in individual metallic nanorods
International audienceWe report on the observation of second-order infrared (IR) plasmon resonances in lithographically prepared gold nanorods investigated by means of far-field microscopic IR spectroscopy. In addition to the fundamental antennalike mode, even and odd higher order resonances are observed under normal incidence of light. The activation of even-order modes under normal incidence is surprising since even orders are dipole-forbidden because of their centrosymmetric charge density oscillation. Performing atomic force microscopy and calculations with the boundary element method, we determine that excitation of even modes is enabled by symmetry breaking by structural deviations of the rods from an ideal, straight shape. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3437093
Strong magnetic response of submicron Silicon particles in the infrared
High-permittivity dielectric particles with resonant magnetic properties are
being explored as constitutive elements of new metamaterials and devices in the
microwave regime. Magnetic properties of low-loss dielectric nanoparticles in
the visible or infrared are not expected due to intrinsic low refractive index
of optical materials in these regimes. Here we analyze the dipolar electric and
magnetic response of loss-less dielectric spheres made of moderate permittivity
materials. For low material refractive index there are no sharp resonances due
to strong overlapping between different multipole contributions. However, we
find that Silicon particles with refractive index 3.5 and radius approx. 200nm
present a dipolar and strong magnetic resonant response in telecom and
near-infrared frequencies, (i.e. at wavelengths approx. 1.2-2 micrometer).
Moreover, the light scattered by these Si particles can be perfectly described
by dipolar electric and magnetic fields, quadrupolar and higher order
contributions being negligible.Comment: 10 pages, 5 figure
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