Extinction correction and on-sky calibration of SCUBA-2

Commissioning of SCUBA-2 included a program of skydips and observations of calibration sources intended to be folded into regular observing as standard methods of source flux calibration and to monitor the atmospheric opacity and stability. During commissioning, it was found that these methods could also be utilised to characterise the fundamental instrument response to sky noise and astronomical signals. Novel techniques for analysing on-sky performance and atmospheric conditions are presented, along with results from the calibration observations and skydips.Comment: 10 pages, 7 figure

Effect of backscattering in phase conjugation with weak scatterers

An extension is presented of a recently developed theory (based on the first Born approximation) of cancellation of distortions by phase conjugation. The influence of backscattering of both the incident and the conjugate waves is considered. It is shown that, when backscattering is taken into account, distortions are not eliminated by phase conjugation, except when the conjugate wave is generated without a loss or a gain

Scattering theory of distortion correction by phase conjugation

The correction of wave distortions by the technique of optical phase conjugation is examined first on the basis of a newly derived integral equation for scattering of monochromatic scalar waves in the presence of a phase-conjugate mirror. The solution is developed in an iterative series, and the first- and second-order terms are analyzed and illustrated diagrammatically. A generalization of the integral equation is then presented, which takes into account the electromagnetic nature of light. It is also shown that, if the conjugate wave is generated without losses or gains and with a complete reversal of polarization, a total elimination of distortions may be achieved by this technique under circumstances that frequently occur in practice

Loss optimization in double fishnet metamaterials at telecommunication wavelengths

A hole shape optimization study was made for a double fishnet metamaterial producing a negative index of refraction within 1.4 - 1.5 μm. It is found that within these wavelengths, elliptical holes offer lower losses as compared to rectangular ones and theoretically produce the best figure of merit (FOM) of approximately 6

One-step fabrication of polymer components for microphotonics by gray scale electron beam lithography

We demonstrate an application of gray scale electron beam lithography (EBL) for fabrication of three dimensional polymer waveguides and grating output couplers using the SU-8 resist. The groove depths of structure are controlled by choosing a proper exposure dose. Unlike reactive ion etching which is limited by the lag effect, the gray scale EBL allows free combination of groove widths and depths. Shrinking effect which is critical in polymer couplers' writing is taken into account and can be compensated. For better fabrication feasibility, the grating couplers can be simultaneously produced with waveguides with no inter-step alignment required. Therefore, this is a promising technique in manufacturing grating output couplers for polymer based waveguides with high performance in terms of mode matching/confinement and coupling efficiency

Mode suppression in a microcavity solid-state dye laser

A solid-state dye laser with a microcavity whose size is comparable to the lasing wavelength, is modeled by means of the finite element method. The position of the pumping source affects the lasing mode spectrum. In comparison with a single point source at the edge of the cavity, a random distribution of excitation sources in the central gain part of the microcavity leads to suppression of odd longitudinal modes and to higher output efficiency of the laser radiation in even modes. The modeling and simulation results are explained by simple physical considerations

Soliton back-action evading measurement using spectral filtering

We report on a back-action evading (BAE) measurement of the photon number of fiber optical solitons operating in the quantum regime. We employ a novel detection scheme based on spectral filtering of colliding optical solitons. The measurements of the BAE criteria demonstrate significant quantum state preparation and transfer of the input signal to the signal and probe outputs exiting the apparatus, displaying the quantum-nondemolition (QND) behavior of the experiment.Comment: 5 pages, 5 figure

Rigorous modeling and physical interpretation of terahertz near-field imaging

Apertureless scanning near-field optical microscopy (SNOM) operating with terahertz (THz) laser pulses is a subject of great research interest. The Mie scattering theory is commonly used to explain the features of the optical waves produced by field interactions with SNOM tips and microstructures. However, since Mie scattering fails with SNOMs at submillimeter wavelengths, a rigorous model and analysis are desirable to assess the feasibility of the THz tip-enhanced scanning near-field techniques. In this paper, we present a numerical simulation of an apertureless SNOM imaging system in the THz band. A 2-dimensional model based on the finite element method (FEM) is investigated and discussed. The modeling results are in good agreement with the experimental data obtained for this system at 2 THz radiation [H.-T. Chen at al., Phys. Rev. Lett. 93, 267401 (2004)]. Additionally, a physical interpretation using the antenna theory is successfully confirmed by the simulation results

Radiative properties of carriers in CdSe-CdS core-shell heterostructured nanocrystals of various geometries

We report a model on core-shell heterostructured nanocrystals with CdSe as the core and CdS as the shell. The model is based on one-band Schrödinger equation. Three different geometries, nanodot, nanorod, and nanobone, are implemented. The carrier localization regimes with these structures are simulated, compared, and analyzed. Based on the electron and hole wave functions, the carrier overlap integral that has a great impact on stimulated emission is further investigated numerically by a novel approach. Furthermore, the relation between the nanocrystal size and electron-hole recombination energy is also examined

Electroencephalography (EEG) for neurological prognostication after cardiac arrest and targeted temperature management; rationale and study design.

BACKGROUND: Electroencephalography (EEG) is widely used to assess neurological prognosis in patients who are comatose after cardiac arrest, but its value is limited by varying definitions of pathological patterns and by inter-rater variability. The American Clinical Neurophysiology Society (ACNS) has recently proposed a standardized EEG-terminology for critical care to address these limitations. METHODS/DESIGN: In the TTM-trial, 399 post cardiac arrest patients who remained comatose after rewarming underwent a routine EEG. The presence of clinical seizures, use of sedatives and antiepileptic drugs during the EEG-registration were prospectively documented. DISCUSSION: A well-defined terminology for interpreting post cardiac arrest EEGs is critical for the use of EEG as a prognostic tool. TRIAL REGISTRATION: The TTM-trial is registered at ClinicalTrials.gov (NCT01020916)