209 research outputs found
Characterization of a Quantum Light Source Based on Spontaneous Parametric Down-Conversion
We have built a quantum light source capable of producing different types of
quantum states. The quantum light source is based on entangled state
preparation in the process of spontaneous parametric down-conversion. The
single-photon detection rate of eight-hundred thousand per second demonstrates
that we have created a bright state-of-the-art quantum light source. As a part
of the characterization we measured two-photon quantum interference in a
Hong-Ou-Mandel interferometer.Comment: 33 page
Signature of a three-dimensional photonic band gap observed on silicon inverse woodpile photonic crystals
We have studied the reflectivity of CMOS-compatible three-dimensional silicon
inverse woodpile photonic crystals at near-infrared frequencies.
Polarization-resolved reflectivity spectra were obtained from two orthogonal
crystal surfaces corresponding to 1.88 pi sr solid angle. The spectra reveal
broad peaks with high reflectivity up to 67 % that are independent of the
spatial position on the crystals. The spectrally overlapping reflectivity peaks
for all directions and polarizations form the signature of a broad photonic
band gap with a relative bandwidth up to 16 %. This signature is supported with
stopgaps in plane wave bandstructure calculations and with the frequency region
of the expected band gap.Comment: 9 pages, 5 figure
Observation of nonlinear bands in near-field scanning optical microscopy of a photonic-crystal waveguide
We have measured the photonic bandstructure of GaAs photonic-crystal
waveguides with high energy and momentum resolution using near-field scanning
optical microscopy. Intriguingly, we observe additional bands that are not
predicted by eigenmode solvers, as was recently demonstrated by Huisman et al.
[Phys. Rev. B 86, 155154 (2012)]. We study the presence of these additional
bands by performing measurements of these bands while varying the incident
light power, revealing a non-linear power dependence. Here, we demonstrate
experimentally and theoretically that the observed additional bands are caused
by a waveguide-specific near- field tip effect not previously reported, which
can significantly phase-modulate the detected field.Comment: 6 pages, 5 figure
Observation of sub-Bragg diffraction of waves in crystals
We investigate the diffraction conditions and associated formation of
stopgaps for waves in crystals with different Bravais lattices. We identify a
prominent stopgap in high-symmetry directions that occurs at a frequency below
the ubiquitous first-order Bragg condition. This sub-Bragg diffraction
condition is demonstrated by reflectance spectroscopy on two-dimensional
photonic crystals with a centred rectangular lattice, revealing prominent
diffraction peaks for both the sub-Bragg and first-order Bragg condition. These
results have implications for wave propagation in 2 of the 5 two-dimensional
Bravais lattices and 7 out of 14 three-dimensional Bravais lattices, such as
centred rectangular, triangular, hexagonal and body-centred cubic
The origin of the [C II] emission in the S140 PDRs - new insights from HIFI
Using Herschel's HIFI instrument we have observed [C II] along a cut through
S140 and high-J transitions of CO and HCO+ at two positions on the cut,
corresponding to the externally irradiated ionization front and the embedded
massive star forming core IRS1. The HIFI data were combined with available
ground-based observations and modeled using the KOSMA-tau model for photon
dominated regions. Here we derive the physical conditions in S140 and in
particular the origin of [C II] emission around IRS1. We identify three
distinct regions of [C II] emission from the cut, one close to the embedded
source IRS1, one associated with the ionization front and one further into the
cloud. The line emission can be understood in terms of a clumpy model of
photon-dominated regions. At the position of IRS1, we identify at least two
distinct components contributing to the [C II] emission, one of them a small,
hot component, which can possibly be identified with the irradiated outflow
walls. This is consistent with the fact that the [C II] peak at IRS1 coincides
with shocked H2 emission at the edges of the outflow cavity. We note that
previously available observations of IRS1 can be well reproduced by a
single-component KOSMA-tau model. Thus it is HIFI's unprecedented spatial and
spectral resolution, as well as its sensitivity which has allowed us to uncover
an additional hot gas component in the S140 region.Comment: accepted for publication in Astronomy and Astrophysics (HIFI special
issue
Suppression of soft nuclear bremsstrahlung in proton-nucleus collisions
Photon energy spectra up to the kinematic limit have been measured in 190 MeV
proton reactions with light and heavy nuclei to investigate the influence of
the multiple-scattering process on the photon production. Relative to the
predictions of models based on a quasi-free production mechanism a strong
suppression of bremsstrahlung is observed in the low-energy region of the
photon spectrum. We attribute this effect to the interference of photon
amplitudes due to multiple scattering of nucleons in the nuclear medium.Comment: 12 pages, 3 figures, submitted to Phys. Rev. Let
Non-isothermal model for the direct isotropic/smectic-A liquid crystalline transition
An extension to a high-order model for the direct isotropic/smectic-A liquid
crystalline phase transition was derived to take into account thermal effects
including anisotropic thermal diffusion and latent heat of phase-ordering.
Multi-scale multi-transport simulations of the non-isothermal model were
compared to isothermal simulation, showing that the presented model extension
corrects the standard Landau-de Gennes prediction from constant growth to
diffusion-limited growth, under shallow quench/undercooling conditions.
Non-isothermal simulations, where meta-stable nematic pre-ordering precedes
smectic-A growth, were also conducted and novel non-monotonic
phase-transformation kinetics observed.Comment: First revision: 20 pages, 7 figure
Multicenter phase II trial of accelerated cisplatin and high-dose epirubicin followed by surgery or radiotherapy in patients with stage IIIa non-small-cell lung cancer with mediastinal lymph node involvement (N2-disease)
To assess the therapeutic activity of accelerated cisplatin and high-dose epirubicin with erythropoietin and G-CSF support as induction therapy for patients with stage IIIa-N2 non-small-cell lung cancer (NSCLC). Patients with stage IIIa-N2 NSCLC were enrolled in a phase II trial. They received cisplatin 60âmgâmâ2 and epirubicin 135âmgâmâ2 every 2 weeks for three courses combined with erythropoietin and G-CSF. Depending on results of clinical response to induction therapy and restaging, patients were treated with surgery or radiotherapy. In total, 61 patients entered from March 2001 to April 2004. During 169 courses of induction chemotherapy, National Cancer Institute of Canada (NCI-C) grade III/IV leucocytopenia was reported in 35 courses (20.7%), NCI-C grade III/IV thrombocytopenia in 26 courses (15.4%) and NCI-C grade III/IV anaemia in six courses (3.6%). Main cause of cisplatin dose reduction was nephrotoxicity (12 courses). Most patients received three courses. There were no chemotherapy-related deaths. Three patients were not evaluable for clinical response. Twenty-eight patients had a partial response (48.3%, 95% CI: 36â61.1%), 24 stable disease and six progressive disease. After induction therapy, 30 patients underwent surgery; complete resection was achieved in 19 procedures (31.1%). Radical radiotherapy was delivered to 25 patients (41%). Six patients were considered unfit for further treatment. Median survival for all patients was 18 months. Response rate of accelerated cisplatin and high-dose epirubicin as induction chemotherapy for stage IIIa-N2 NSCLC patients is not different from more commonly used cisplatin-based regimen
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