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Long [gamma]-ray bursts are associated with energetic, broad-lined, stripped-envelope supernovae.sup.1,2 and as such mark the death of massive stars. The scarcity of such events nearby and the brightness of the [gamma]-ray burst afterglow, which dominates the emission in the first few days after the burst, have so far prevented the study of the very early evolution of supernovae associated with [gamma]-ray bursts.sup.3. In hydrogen-stripped supernovae that are not associated with [gamma]-ray bursts, an excess of high-velocity (roughly 30,000 kilometres per second) material has been interpreted as a signature of a choked jet, which did not emerge from the progenitor star and instead deposited all of its energy in a thermal cocoon.sup.4. Here we report multi-epoch spectroscopic observations of the supernova SN 2017iuk, which is associated with the [gamma]-ray burst GRB 171205A. Our spectra display features at extremely high expansion velocities (around 115,000 kilometres per second) within the first day after the burst.sup.5,6. Using spectral synthesis models developed for SN 2017iuk, we show that these features are characterized by chemical abundances that differ from those observed in the ejecta of SN 2017iuk at later times. We further show that the high-velocity features originate from the mildly relativistic hot cocoon that is generated by an ultra-relativistic jet within the [gamma]-ray burst expanding and decelerating into the medium that surrounds the progenitor star.sup.7,8. This cocoon rapidly becomes transparent.sup.9 and is outshone by the supernova emission, which starts to dominate the emission three days after the burst.Multi-epoch observations of a supernova associated with a [gamma]-ray burst reveal spectral features at extremely high expansion velocities within the first day after the burst, indicative of a choked jet., Author(s): L. Izzo [sup.1] , A. de Ugarte Postigo [sup.1] [sup.2] , K. Maeda [sup.3] , C. C. Thöne [sup.1] , D. A. Kann [sup.1] , M. Della Valle [sup.1] [...]

Tunable materials with high anisotropy of refractive index and low loss are of particular interest in the microwave and terahertz range. Nematic liquid crystals are highly sensitive to electric and magnetic fields and may be designed to have particularly high birefringence. In this paper we investigate birefringence and absorption losses in an isothiocyanate based liquid crystal (designed for high anisotropy) in a broad range of the electromagnetic spectrum, namely 0.1-4 GHz 30 GHz, 0.5-1.8 THz, and in the visible and near-infrared region (400 nm-1600 nm). We report high birefringence (An = 0.19 - 0.395) and low loss in this material. This is attractive for tunable microwave and terahertz device applications. OCIS codes: 300.6390, 300.6495, 300.6550, 160.3710.

The absorption and scattering properties of three developmental stages of protozoan parasite Plasmodium falciparum were studied both experimentally and theoretically. Experimentally, the light attenuation and forward scattering from parasites extracted from host erythrocyte cultures were measured with UV--visible spectroscopy. The measured spectra were interpreted theoretically with a model based on the core-shell Mie theory in terms of the structural and compositional characteristics of the protozoa. The model accurately reproduced the features of the measured spectra of all developmental stages. The results show that realistic quantitative estimates of the parasite size, nucleotide, and hemozoin contents can be derived from the UV--visible spectroscopy measurements. OCIS codes: 300.0300, 170.1530.

The goal of the current study was to introduce a mathematical method to derive hemoglobin, oxyhemoglobin and carboxyl-hemoglobin absorption factors from full spectrum reflectometry measurements of retinal microcapillaries. The mathematical equation that describes the spectral reflectometry function was expressed as a linear combination of several terms of [S.sub.i] ([lambda]) representing the spectral signature functions of hemoglobin, oxyhemoglobin, carboxyl-hemoglobin, ocular media, melanin, and a scattering factor. Contrary to the classical model, where the reflectometry function was expressed as an absorbance Ab([lambda]) = log(incident light([lambda])/reflected light([lambda])), in this model and system, it is proposed to express the reflectometry function from the eye structures as an absorption factor A([lambda])% = incident light([lambda])/ reflected light([lambda]). To increase confidence in the estimation of hemoglobin derivatives, the mathematical model was applied to only a part of the spectral function of reflectometry, while the results of the model were used to explain the other part of the reflectometry function. The results demonstrate that for the visible spectral field, the model that explains the absorption of the light by the blood contained in the microcapillaries of biological structures is not compatible with the Beer-Lambert law. OCIS codes: 170.1460, 170.3890.

A method to determine the thickness of a nonabsorbing thin film on an absorbing substrate is presented. A linear relation between the thin-film thickness and the tangent wavelength of the reflectance spectrum for a specific interference order is revealed, which permits the calculation of the thickness provided that the wavelength-dependent optical parameters of the thin film and the substrate are known. The thickness can be calculated precisely from the reflectance spectrum by using one extreme only, as is demonstrated theoretically for Si[O.sub.2] thin film on a Si substrate. The application of this method is demonstrated experimentally for the same thin-film structure but with different Si substrates. The results are compared with those given by the algebraic fitting method, and very good agreement is confirmed. OCIS codes: 240.0310, 120.4530.

We extend the approach recently applied for achieving spatial and temporal superresolution to spectral measurements with superresolution. The light passes previously through a filter with a periodic spectral response. Owing to the spectral modulation, the parts of the spectrum Fourier transform are shifted and transmitted through the passband of the Fourier transform of the spectrometer instrumental function. Thus, all the parts of the spectrum Fourier transform are recorded by the spectrometer and then restored by a special procedure. An inverse Fourier transform gives the spectrum restored with superresolution. We numerically demonstrate more than tenfold enhancement of the resolution by using a sampled fiber Bragg grating for spectral modulation. OCIS codes: 300.6320, 060.3735, 070.2615, 070.4790.

The 2007 Measurement Problem comprised measurements of the transmission and reflectance spectra and the determination of optical constants for a single oxide layer on fused silica. The angle of incidence was 45[degrees]. OCIS codes: 120.4530, 310.6860.

A goniofluorometer has been built that is capable of measuring in various viewing angles ranging from 10[degrees] to 90[degrees]. The incident angle can be varied from 0[degrees] to 8[degrees]. The goniofluorometer can measure bispectral luminescent radiance factors in the wavelength range of 250-800 nm. To our knowledge, there are no other reported results of similar devices capable of spectral measurements in various measurement geometries. OCIS codes: 120.3930, 120.3940, 120.4800, 120.6200.

Infrared remote detection of chemical and biological agents in a complex environment depends on the ability to recognize threat signatures and differentiate them from the signatures of innocuous materials. In this paper, we addressed the methods of producing the constraint spectra needed to ensure reliable operation in a meteorologically changing environment. We collected arrays of background spectra of ground, woods, and low-angle sky on an irregular basis over a period of a year. Based on the hypothesis that the concentration fluctuations of species in the sensor's field of view can be exploited to form signatures, the standard deviations of the array (the result is characteristic of all fluctuations) and the difference array (the result is characteristic of sensor fluctuations) were computed. Subtracting these two spectra and filtering the result produced a spectrum, which is a measure of the IR fluctuations in the scene. The resulting set of scene spectra were processed into aberrant noise, and deterministic groups by numerical filtering and statistical methods. OCIS codes: 010.1120, 030.5630, 280.1120, 300.6340.

Astrophys. J. 710, L35-L38 (2010) Astronomers have for the first time directly captured the spectrum of light emitted by a planet orbiting a Sun-like star outside the Solar System. Space [...]