214 research outputs found
Recombination Ghosts in Littrow Configuration: Implications for Spectrographs Using Volume Phase Holographic Gratings
We report the discovery of optical ghosts generated when using Volume Phase
Holographic (VPH) gratings in spectrographs employing the Littrow
configuration. The ghost is caused by light reflected off the detector surface,
recollimated by the camera, recombined by, and reflected from, the grating and
reimaged by the camera onto the detector. This recombination can occur in two
different ways. We observe this ghost in two spectrographs being developed by
the University of Wisconsin - Madison: the Robert Stobie Spectrograph for the
Southern African Large Telescope and the Bench Spectrograph for the WIYN 3.5m
telescope. The typical ratio of the brightness of the ghost relative to the
integrated flux of the spectrum is of order 10^-4, implying a recombination
efficiency of the VPH gratings of order 10^-3 or higher, consistent with the
output of rigorous coupled wave analysis. Any spectrograph employing VPH
gratings, including grisms, in Littrow configuration will suffer from this
ghost, though the general effect is not intrinsic to VPH gratings themselves
and has been observed in systems with conventional gratings in non-Littrow
configurations. We explain the geometric configurations that can result in the
ghost as well as a more general prescription for predicting its position and
brightness on the detector. We make recommendations for mitigating the ghost
effects for spectrographs and gratings currently built. We further suggest
design modifications for future VPH gratings to eliminate the problem entirely,
including tilted fringes and/or prismatic substrates. We discuss the resultant
implications on the spectrograph performance metrics.Comment: 13 pages, 8 figures, emulateapj style, accepted for publication in
PAS
Charge oscillation-induced light transmission through subwavelength slits and holes
We present a concrete picture of spoof surface plasmons (SSPs) combined with
cavity resonance to clarify the basic mechanism underlying extraordinary light
transmission through metal films with subwavelength slits or holes. This
picture may indicate a general mechanism of metallic nanostructure optics: When
light is incident on a non-planar conducting surface, the free electrons cannot
move homogeneously in response to the incident electric field, i.e., their
movement can be impeded at the rough parts, forming inhomogeneous charge
distributions. The oscillating charges/dipoles then emit photons (similar to
Thomson scattering of x rays by oscillating electrons), and the interference
between the photons may give rise to anomalous transmission, reflection or
scattering.Comment: 4 pages, 4 figures, are "surface plasmons" true for conducting
structures? Answere is here. Also see the new arXiv:0903.3565v1, the
expansion of this pape
Scattering mechanism in a step-modulated subwavelength metal slit: a multi-mode multi-reflection analysis
In this paper, the scattering/transmission inside a step-modulated
subwavelength metal slit is investigated in detail. We firstly investigate the
scattering in a junction structure by two types of structural changes. The
variation of transmission and reflection coefficients depending on structural
parameters are analyzed. Then a multi-mode multi-reflection model based on ray
theory is proposed to illustrate the transmission in the step-modulated slit
explicitly. The key parts of this model are the multi-mode excitation and the
superposition procedure of the scatterings from all possible modes, which
represent the interference and energy transfer happened at interfaces. The
method we use is an improved modal expansion method (MEM), which is a more
practical and efficient version compared with the previous one [Opt. Express
19, 10073 (2011)]. In addition, some commonly used methods, FDTD, scattering
matrix method, and improved characteristic impedance method, are compared with
MEM to highlight the preciseness of these methods.Comment: 25 pages, 9 figure
Impedance model for the polarization-dependent optical absorption of superconducting single-photon detectors
We measured the single-photon detection efficiency of NbN superconducting
single photon detectors as a function of the polarization state of the incident
light for different wavelengths in the range from 488 nm to 1550 nm. The
polarization contrast varies from ~5% at 488 nm to ~30% at 1550 nm, in good
agreement with numerical calculations. We use an optical-impedance model to
describe the absorption for polarization parallel to the wires of the detector.
For lossy NbN films, the absorption can be kept constant by keeping the product
of layer thickness and filling factor constant. As a consequence, we find that
the maximum possible absorption is independent of filling factor. By
illuminating the detector through the substrate, an absorption efficiency of
~70% can be reached for a detector on Si or GaAs, without the need for an
optical cavity.Comment: 15 pages, 5 figures, submitted to Journal of Applied Physic
Fabrication of subwavelength structured surfaces via electrospray deposition of nanobeads
The usability of electrospray deposition (ESD) to form antireflection structured (ARS) surfaces was studied experimentally. Subwavelength structured (SWS) surfaces were produced by depositing nanobeads with diameters of 50 nm onto glass substrates covered with an ITO-Film. The reflectance from the substrates could be decreased about nearly 3% with an onesided ARS surface
Discrepancy between German S3 Guideline Recommendations and Daily Urologic Practice in the Management of Nonmuscle Invasive Bladder Cancer: Results of a Binational Survey
Introduction: Guideline recommendations are meant to help minimize morbidity and to improve the care of nonmuscle invasive bladder cancer (NMIBC) patients but studies have suggested an underuse of guideline-recommended care. The aim of this study was to evaluate the level of adherence of German and Austrian urologists to German guideline recommendations. Methods: A survey of 27 items evaluating diagnostic and therapeutic recommendations (15 cases of strong consensus and 6 cases of consensus) for NMIBC was administered among 14 urologic training courses. Survey construction and realization followed the checklist for reporting results of internet e-surveys and was approved by an internal review board. Results: Between January 2018 and June 2019, a total of 307 urologists responded to the questionnaire, with a mean response rate of 71%. The data showed a weak role of urine cytology (54%) for initial diagnostics although it is strongly recommended by the guideline. The most frequently used supporting diagnostic tool during transurethral resection of the bladder was hexaminolevulinate (95%). Contrary to the guideline recommendation, 38% of the participants performed a second resection in the case of pTa low-grade NMIBC. Correct monitoring of Bacille Calmette-Guerin (BCG) response with cystoscopy and cytology was performed by only 34% of the urologists. Conclusions: We found a discrepancy between certain guideline recommendations and daily routine practice concerning the use of urine cytology for initial diagnostics, instillation therapy with a low monitoring rate of BCG response, and follow-up care with unnecessary second resection after pTa low-grade NMIBC in particular. Our survey showed a moderate overall adherence rate of 73%. These results demonstrate the need for sharpening awareness of German guideline recommendations by promoting more intense education of urologists to optimize NMIBC care thus decreasing morbidity and mortality rates
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