511 research outputs found
Limits of Kirchhoff's Laws in Plasmonics
Get PDFThe validity of Kirchhoff's laws in plasmonic nanocircuitry is investigated by studying a junction of plasmonic two-wire transmission lines. We find that Kirchhoff's laws are valid for sufficiently small values of a phenomenological parameter κ relating the geometrical parameters of the transmission line with the effective wavelength of the guided mode. Beyond such regime, for large values of the phenomenological parameter, increasing deviations occur and the equivalent impedance description (Kirchhoff's laws) can only provide rough, but nevertheless useful, guidelines for the design of more complex plasmonic circuitry. As an example we investigate a system composed of a two-wire transmission line and a nanoantenna as the load. By addition of a parallel stub designed according to Kirchhoff's laws we achieve maximum signal transfer to the nanoantenna
Principles of nano-optics / Lukas Novotny, Bert Hecht.
No full textIncludes bibliographical references and index.xvii, 539 pages :Nano-optics is the study of optical phenomena and techniques on the nanometer scale, that is, near or beyond the diffraction limit of light. It is an emerging field of study, motivated by the rapid advance of nanoscience and nanotechnology which require adequate tools and strategies for fabrication, manipulation and characterization at this scale. In this 2006 text the authors provide a comprehensive overview of the theoretical and experimental concepts necessary to understand and work in nano-optics. With a very broad perspective, they cover optical phenomena relevant to the nanoscale across diverse areas ranging from quantum optics to biophysics, introducing and extensively describing all of the significant methods. Written for graduate students who want to enter the field, the text includes problem sets to reinforce and extend the discussion. It is also a valuable reference for researchers and course teachers
Single-molecule nano-optics at low temperature
Get PDFThe work presented in this thesis involves experiments on single molecules at low
temperature. At low temperature, many disturbing temperature activated processes
are frozen out, resulting in extremely sharp zero-phonon lines in the fluorescence ex-
citation spectra of certain molecule-matrix systems. The presence of sharp absorp-
tion lines is accompanied by the fact that the absorption cross-section is significantly
increased, approaching a value of about 10% of the theoretical limit for an oscillating
dipole.
The first part of this thesis provides background information for understanding
the experimental results. It introduces the energy level scheme of a single mole-
cule in a solid matrix at low temperature, the methods to get down to the single-
molecule level, the requirements for a molecule-matrix system for single-molecule
spectroscopy, the absorption cross-section and saturation. After this theoretical
part, the experimental techniques used for the experiments in this thesis, confocal
microscopy and aperture scanning near-field optical microscopy, are discussed.
This theoretical part is followed by an experimental part, which describes the
combined home-built confocal and aperture scanning near-field optical microscope
working at 1.8 K in a helium bath cryostat. It starts with a general overview,
followed by detailed descriptions of the most important parts of the set up. The
last part of the experimental section describes the preparation of the two different
samples used in these studies: terrylene doped into crystals of p-terphenyl and
terrylene in a stretched film of linear low-density polyethylene.
The second part of this thesis describes the experimental results. It starts
with a study of the imaging properties of single molecules at low temperature as a
function of excitation frequency and excitation intensity. Molecules are imaged at
several spectral positions on their resonance curve. The spot sizes of single molecules
appear increased in resonance compared to the out-of-resonance values and increase
with excitation intensity. With the help of Monte Carlo simulations, addressing the
measured spot size as a function of detuning (i.e. decreasing signal-to-background
ratio) and as a function of intensity, the observed effects could be attributed to
pronounced saturation effects in single-molecule imaging. In fact, the spot size of a
single molecule turns out to increase with intensity, even below saturation.
After this first experiment, the main experiment of this thesis is described. It
starts with the characterisation of a new sample for single-molecule spectroscopy
at low temperature, terrylene in a stretched film of linear low-density polyethylene.
Terrylene molecules in a stretched film of linear low-density polyethylene are all ori-
ented along the stretching direction and show su±cient spectral stability. The degree
of orientation turns out to include all three dimensions. The molecules all have their
transition dipole moments aligned in the sample plane, which leads to a maximised
absorption cross-section. The maximised absorption cross-section of the terrylene
molecules makes this sample a good candidate for single-molecule detection by ab-
sorption. Single molecule detection by absorption is the main experiment described
in this thesis. Despite the conceptual ease of performing a bulk absorption exper-
iment, single-molecule detection by absorption is often considered hardly possible:
the excitation and emission wavelength are exactly the same and the detector is di-
rectly exposed to high intensity laser light. Single-molecule detection by absorption
exploits the fact that the coherent part of light emitted by the molecule can interfere
in the far field with the excitation light. Due to a phase difference between the light
scattered resonantly by the molecule and the reflected excitation light, a dispersive
signal is observed on scanning the excitation frequency over the resonance of a single
molecule. Single molecules are thus detected in absorption as dispersive features.
Absorption and fluorescence excitation spectra are recorded simultaneously. From
fluorescence excitation spectra, the exact spectral position and line width of single
molecules were determined, which facilitated the analysis of the absorption spectra.
Dynamical features, like blinking and spectral jumping, are observed. From the
amplitudes of the absorption signal and the line width of the signals, a negative
correlation between line width and amplitude was found. This confirms the physical
principle that the amount of coherently scattered light decreases upon saturation
or due to dephasing. Unfortunately, the signal-to-background ratio of absorption
spectra is still rather low compared to fluorescence excitation spectra. A method to
improve the signal-to-background ratio could be to go to near-field excitation
Ep. #055 - Gabrielle Hecht
No full textThis recording and transcript form part of a collection of podcasts conducted by the Cultures of Energy at Rice University. Cultures of Energy brings writers, artists and scholars together to talk, think and feel their way into the Anthropocene. We cover serious issues like climate change, species extinction and energy transition. But we also try to confront seemingly huge and insurmountable problems with insight, creativity and laughter.In a fittingly bizarre intro for these political times, Cymene and Dominic share weird fantasies and actual plans for resistance. We then (11:57) welcome to the podcast renowned historian and ethnographer of nuclear energy, Gabrielle Hecht from the University of Michigan, author of Being Nuclear and The Radiance of France (MIT Press). Gabrielle tells us why she first became interested in nuclear power growing up in Reagan’s Cold War. We compare fears of nuclear war then and now and explore different historical constructions of “the nuclear” more generally. We talk about her concept of “toxic infrastructure” and how it can apply to places like Flint, Michigan. Gabrielle then explains how France became the country in the world most reliant upon nuclear energy for its electricity and why the French nuclear industry is in now in such a state of panic. We talk about why nuclear energy hasn’t lost its utopianism—including as a climate change fix—but why we think the nuclear solution to global warming is a red herring. We turn to Fukushima and Gabrielle reminds us that it’s also important to pay attention to the less spectacular but more common environmental and human impacts of using nuclear fuel, including the fate of people who clean reactors under normal and catastrophic conditions. We discuss uranium mining in Africa and the struggles miners have fought to have their “biological citizenship” recognized by their governments. That leads us to talk about the real costs of nuclear energy. And we close on Gabrielle’s latest work on toxicity and what she calls the African Anthropocene. Hang in there, everyone, be kind to yourselves and stay strong for the long run of resistance
Single emitters coupled to bow-tie nano-antennas
Get PDFApproaching a metallic tip to a single quantum emitter quenches the photolumi-
nescence by opening non-radiative decay channels for the excited-state. This is
one of the main problems in nano-optics research which prohibits optical studies
on single emitters in contact with the tip with high resolution and high sensitivity.
In this thesis I have shown that a bowtie nanoantenna can be used to overcome
the quenching problem at the single chromophore level. Bowtie antenna tip in-
teracts with the dipole of the single emitter. This is most probably the ¯rst study
on this type of measurements which opens new pathways for many disciplines.
Semiconductor nanocrystals were selected as a single emitter system due to their
relatively high photo-stability. Based on °uorescence confocal studies, satura-
tion behavior of single CdSefZnSg nanocrystal (NC) is studied under one- and
two-photon excitation. In one-photon excitation (1PE) laser wavelength of 532
nm and in two-photon excitation (2PE) laser wavelength of 830 nm were used
to excite the °uorophore. Due to the broad distribution in photoluminescence
(PL) intensity of nanocrystals, power dependence studies were done based on
an average over » 90 nanocrystals. Using focused ion beam, bowtie antennas
are sculptured at the apices of silicon nitride AFM tips, which were fully-coated
with a homogeneous layer of 40 nm of aluminum ¯lm. Details of structuring
procedures used to fabricate well-de¯ned bowtie antennas with smallest possible
feedgaps are described. Interaction of bowtie nanoantennas with single semicon-
ductor nanocrystals, is investigated using PL intensity and excited-state lifetime
of the nanocrystal as two intrinsic signatures of the single emitter. Proximity of
the feedgap of a bowtie nanoantenna to a single nanocrystal under one-photon
excitation leads to enhanced emission in addition to enhanced excitation. This
e®ect is shown, by increasing the PL intensity of the nanocrystal and shortened
lifetime, in contact with the bowtie antenna feedgap. These results were com-
pared with a fully-coated tip which lead to complete quenching of the nanocrystal
PL. Thus, the observed e®ects in PL intensity and lifetime of the nanocrystal in
contact with the antenna are originated from the metallic nanostructure. Under
two-photon excitation, PL intensity is enhanced but there is no change in the
lifetime of the nanocrystal in contact with the bowtie antenna. This is caused by
enhanced excitation through the antenna, induced by enlarging the absorption
cross section of the nanocrystal in contact with the antenna. Since, °uorescence
of single nanocrystal in contact with the bowtie antenna is "not quenched", more
detailed studies on their interaction were performed. Under two-photon excita-
tion absorption cross section of one nanocrystal was measured with and without
the presence of antenna. Free nanocrystal showed a two-photon absorption cross
section in the order of 6:3£10¡37cm4s which in contact with the bowtie antenna
increased to 20:2£10¡37cm4s. This proves that enhanced excitation observed in
2PE is caused by a larger absorption cross section of the system induced by the
antenna structure. Emission polarization of nanocrystals was studied under 1PE
using polarization microscopy. From these studies, in- and out-of-plane angles as
well as the absolute value of the projection of the transition dipole moment on
the sample plane were determined. Results showed in contact with the bowtie
antenna, the in-plane angle turns towards the orientation of the antenna. This
is induced by the strong dipole of the antenna in contact with the nanocrystal.
Moreover, modulation depth and the absolute value of the transition dipole were
increased dramatically in contact with the bowtie nanostructure. The results
show that antenna/NC system has a highly polarized emission, whose polar-
ization direction is determined by the antenna dipole. Photon antibunching of
nanocrystals under 1PE was done with and without the presence of the antenna
tip. Shorter lifetime of the excited-state in contact with the bowtie antenna
immediately appears in antibunching results. This shows that the "dead time"
for single photon generation, caused by excitation-recombination cycles, is much
shorter in contact with the antenna. Therefore, a nanocrystal in contact with
the bowtie antenna is a more e±cient single photon source. Moreover, taking
into account the emission polarization of the antenna/NC system, polarization of
single photons generated from the nanocrystal in contact with the antenna can
be tuned by antenna orientation. Thus, single photons provided by antenna/NC
system can have strong potentials in quantum cryptography. As a result, coupling
single quantum emitters (here nanocrystal) to bowtie nanoantennas will produce
a new type of emitter with widely adjustable photophysical properties, which can
be called a "tunable superemitter". Emission characteristics of the antenna/NC
system is highly determined by the coupling intra-superemitter
[Letter on the history of the community of Maroldsweisach, Bavaria] /
No full textTypescripton with a brief description, including a bit of historical information, of the Jewish community in Maroldsweisach, Bavaria, during the early 20th century. The letter focuses on the family of the author Ralph Hecht, and includes some information on the persecutions during the National Socialist dictatorship.Ralph HechtThe original German-language inventory is available in the folder.Processed for digitizationReturned from digitizationdigitize
Nanoantennas for visible and infrared radiation
No full textNanoantennas for visible and infrared radiation can strongly enhance the interaction of light with nanoscale matter by their ability to efficiently link propagating and spatially localized optical fields. This ability unlocks an enormous potential for applications ranging from nanoscale optical microscopy and spectroscopy over solar energy conversion, integrated optical nanocircuitry, opto-electronics and density-of-states engineering to ultra-sensing as well as enhancement of optical nonlinearities. Here we review the current understanding of metallic optical antennas based on the background of both well-developed radiowave antenna engineering and plasmonics. In particular, we discuss the role of plasmonic resonances on the performance of nanoantennas and address the influence of geometrical parameters imposed by nanofabrication. Finally, we give a brief account of the current status of the field and the major established and emerging lines of investigation in this vivid area of research
Normal-Incidence PEEM Imaging of Propagating Modes in a Plasmonic Nanocircuit
No full textThe
design of noble-metal plasmonic devices and nanocircuitry requires
a fundamental understanding and control of the interference of plasmonic
modes. Here we report the first visualization of the propagation and
interference of guided modes in a showcase plasmonic nanocircuit using
normal-incidence nonlinear two-photon photoemission electron microscopy
(PEEM). We demonstrate that in contrast to the commonly used grazing-incidence
illumination scheme, normal-incidence PEEM provides a direct image
of the structure’s near-field intensity distribution due to
the absence of beating patterns and despite the transverse character
of the plasmonic modes. Based on a simple heuristic numerical model
for the photoemission yield, we are able to model all experimental
findings if global plane wave illumination and coupling to multiple
input/output ports, and the resulting interference effects are accounted
for
Germanium Fabry-Perot nanoresonators investigated by cathodoluminescence spectroscopy
Get PDFWe report on the experimental investigation, by means of spatially-resolved cathodoluminescence spectroscopy, of rectangular all-dielectric Ge nanoantennas sustaining Fabry-Perot resonances. The combination of spatial and spectral resolution allows us to directly image the standing-wave pattern of the local density of optical states inside the nanoantennas, which is the fingerprint of the resonant Purcell contribution to the overall emission enhancement previously reported in the literature for the same structures. Our results confirm that the emission properties of Ge nanostructures can be effectively tuned by engineering the local density of optical states and that cathodoluminescence provides valuable information to experimentally address such modulation in their emission properties
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