Facet machining of silica waveguides with nanoscale roughness without polishing or lapping

To achieve low-loss free space coupling for integrated optics, device facets need to be smooth, free of chips and flat. The typical route for accomplishing these requirements is by traditional lapping and polishing. We report that high quality optical quality facets with a Sa = 4.9 nm can be machined using a simple dicing technique. In order to directly measure the scatter loss a device with a series of Bragg gratings is used to characterise the average interface loss per facet

Enhancing chemical sensitivity of a tilted planar Bragg grating using a thin gold layer

The use of weakly tilted Bragg gratings to couple light from core waveguide modes to plasmon resonances within thin gold layers has gained increased interest over recent years. Chemical sensing using such techniques has a multitude of advantages, including access to developed gold based chemistry for surface functionalisation and an enhancement of chemical sensitivity, particularly for the biochemically ubiquitous solvent, water (1.33). Despite the obvious benefits of such devices, fabrication has principally been limited to optical fibre platforms, with little fabrication development being made in the planar regime. This work reports the use of a thin (50 nm) sputtered gold layer to enhance the chemical sensitivity of a weakly tilted planar Bragg grating (TPBG), illustrated in Figure 1 (a). Therefore, allowing access to the benefits of planar integration for this newly emerging technology

A microflow cytometer for microsphere-based immunoassays using integrated optics and inertial particle focussing

We present work towards a microflow cytometer for performing multiplex immunoassays using commercially available fluorescently-labelled microspheres. The device consists of a silica chip with integrated GeO2:SiO2 channel waveguides which deliver excitation light orthogonally to an etched flow channel [1], [2]. The rectangular cross section, 2:1 aspect ratio flow channel and flow rate create an inertial focussing effect on the microspheres [3] which ensures they flow through the plane of maximum optical excitation, halfway up the height of the channel, with minimal positional variation. The optical waveguide core is fabricated by magnetron sputtering of GeO2:SiO2 films which are then etched to form channel waveguides by ICP etching. The silica cladding, up to 13.5 µm thick, is deposited by either flame hydrolysis deposition or a combination of magnetron sputtering followed by PECVD. Fluidic channels are etched with ICP etching. Channels with the dimensions of 14.1 µm x 27.5 µm and near vertical sidewalls (91°±4°) have been produced in silica as shown in the cross section in Figure 1A. Figure 1B shows a device with the fluidic channel etched through waveguides clad with PECVD silica. Design parameters were established with PDMS test channels 25.5 µm deep by 12.2 µm wide. Figures 2A and 2B show transmission fluorescence imaging of streaks from multiple 5.6µm diameter microspheres flowing at 0.49 m/s down the fluidic channel. The microspheres are shown to be focused into a tight stream at 15 mm from the channel entrance in Figure 2C, indicating the minimum channel length required for the final devices. Future work will include dual channel quantification of microsphere fluorescence and development of an assay for TNFalpha and later multiplex measurements. Collection of fluorescence with channel waveguides and also characterisation of transmission measurements from flowing microspheres will also be studied

Pre-main-sequence population in NGC 1893 region

In this paper we continued our efforts to understand the star formation scenario in and around the young cluster NGC 1893. We used a sample of the young stellar sources (YSOs) identified on the basis of multiwavelength data (optical, near-infrared (NIR), mid-infrared (MIR) and X-ray) to study the nature of YSOs associated with the region. The identified YSOs show an age spread of ~ 5 Myr. The YSOs located near the nebulae at the periphery of the cluster are relatively younger in comparison to those located within the cluster region. The present results are in accordance with those obtained by us in previous studies. Other main results from the present study are: 1) the fraction of disk bearing stars increases towards the periphery of the cluster; 2) there is an evidence supporting the notion that the mechanisms for disk dispersal operate less efficiently for low-mass stars; 3) the sample of Class II sources is found to be relatively older in comparison to that of Class III sources. A comparison of various properties of YSOs in the NGC 1893 region with those in the Tr 37/ IC 1396 region is also discussed.Comment: Accepted for publication in New Astronom

Accretion, Outflows, and Winds of Magnetized Stars

Many types of stars have strong magnetic fields that can dynamically influence the flow of circumstellar matter. In stars with accretion disks, the stellar magnetic field can truncate the inner disk and determine the paths that matter can take to flow onto the star. These paths are different in stars with different magnetospheres and periods of rotation. External field lines of the magnetosphere may inflate and produce favorable conditions for outflows from the disk-magnetosphere boundary. Outflows can be particularly strong in the propeller regime, wherein a star rotates more rapidly than the inner disk. Outflows may also form at the disk-magnetosphere boundary of slowly rotating stars, if the magnetosphere is compressed by the accreting matter. In isolated, strongly magnetized stars, the magnetic field can influence formation and/or propagation of stellar wind outflows. Winds from low-mass, solar-type stars may be either thermally or magnetically driven, while winds from massive, luminous O and B type stars are radiatively driven. In all of these cases, the magnetic field influences matter flow from the stars and determines many observational properties. In this chapter we review recent studies of accretion, outflows, and winds of magnetized stars with a focus on three main topics: (1) accretion onto magnetized stars; (2) outflows from the disk-magnetosphere boundary; and (3) winds from isolated massive magnetized stars. We show results obtained from global magnetohydrodynamic simulations and, in a number of cases compare global simulations with observations.Comment: 60 pages, 44 figure

γ -ray spectroscopy of astrophysically important states in Ca 39

Background: Nova explosions synthesize elements up to A≃40, and discrepancies exist between calculated and observed abundances of Ar and Ca created in the explosion. The K38(p,γ)Ca39 reaction rate has been shown to be influential on these isotopic abundances at the endpoint of nova nucleosynthesis. The energies of the three most important resonances, corresponding to Jπ=5/2+ excited states in the Ca39 nucleus above the proton separation threshold, are uncertain and one has been measured with conflicting values [Er=679(2) versus Er=701(2) keV] in previous experiments. Purpose: Reducing the uncertainties on the resonance energies would allow for a better understanding of the reaction rate. To improve these uncertainties, we searched for γ rays from the depopulation of the corresponding excited states in Ca39. Methods: We report a new measurement of these resonance energies via the observation of previously unobserved γ-ray transitions. These transitions were observed by studying the Ca40(3He,αγ)Ca39 reaction with Gammasphere ORRUBA Dual Detectors for Experimental Structure Studies (GODDESS). The updated resonance energies were then used to calculate the K38(p,γ)Ca39 reaction rate and assess its uncertainties. Results: In total, 23 new transitions were found, including three γ-ray transitions corresponding to the three Jπ=5/2+ states of astrophysical interest at energies of 6156.2(16), 6268.8(22), and 6470.8(19) keV. These correspond to resonance energies in the K38(p,γ)Ca39 reaction of 386(2), 498(2), and 701(2) keV. Conclusions: Updated K38(p,γ)Ca39 reaction rate calculations show a reduced upper limit at nova temperatures. However, the lower-than-previously-measured energy of the 498-keV resonance and uncertainty in its resonance strength increases the upper limit of the rate close to previous estimates at 0.4 GK

New γ -ray transitions observed in Ne 19 with implications for the O 15 (α,γ) Ne 19 reaction rate

The O15(α,γ)Ne19 reaction is responsible for breakout from the hot CNO cycle in type I x-ray bursts. Understanding the properties of resonances between Ex=4 and 5 MeV in Ne19 is crucial in the calculation of this reaction rate. The spins and parities of these states are well known, with the exception of the 4.14- and 4.20-MeV states, which have adopted spin-parities of 9/2- and 7/2-, respectively. γ-ray transitions from these states were studied using triton-γ-γ coincidences from the F19(He3,tγ)Ne19 reaction measured with the GODDESS (Gammasphere ORRUBA Dual Detectors for Experimental Structure Studies) at Argonne National Laboratory. The observed transitions from the 4.14- and 4.20-MeV states provide strong evidence that the Jπ values are actually 7/2- and 9/2-, respectively. These assignments are consistent with the values in the F19 mirror nucleus and in contrast to previously accepted assignments

The Earth: Plasma Sources, Losses, and Transport Processes

This paper reviews the state of knowledge concerning the source of magnetospheric plasma at Earth. Source of plasma, its acceleration and transport throughout the system, its consequences on system dynamics, and its loss are all discussed. Both observational and modeling advances since the last time this subject was covered in detail (Hultqvist et al., Magnetospheric Plasma Sources and Losses, 1999) are addressed