scholarly journals Quasi-BIC laser enabled by high-contrast grating resonator for gas detection

Nanophotonics ◽  
2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Haoran Zhang ◽  
Tao Wang ◽  
Jingyi Tian ◽  
Jiacheng Sun ◽  
Shaoxian Li ◽  
...  
Keyword(s):  
Bound States ◽  
Signal To Noise Ratio ◽  
Bound State ◽  
Gain Medium ◽  
Gas Detection ◽  
Visible Range ◽  
High Signal ◽  
High Contrast ◽  
High Contrast Grating ◽  
The Continuum

Abstract In this work, we propose and numerically investigate a two-dimensional microlaser based on the concept of bound states in the continuum (BIC). The device consists of a thin gain layer (Rhodamine 6G dye-doped silica) sandwiched between two high-contrast-grating layers. The structure supports various BIC modes upon a proper choice of topological parameters; in particular it supports a high-Q quasi-BIC mode when partially breaking a bound state in the continuum at Γ point. The optically-pumped gain medium provides sufficient optical gain to compensate the quasi-BIC mode losses, enabling lasing with ultra-low pump threshold (fluence of 17 μJ/cm2) and very narrow optical linewidth in the visible range. This innovative device displays distinguished sensing performance for gas detection, and the emission wavelength sensitively shifts to the longer wavelength with the changing of environment refractive index (in order of 5 × 10−4). The achieved bulk sensitivity is 221 nm/RIU with a high signal to noise ratio, and a record-high figure of merit reaches to 4420 RIU−1. This ultracompact and low threshold quasi-BIC laser facilitated by the ultra-narrow resonance can serve as formidable candidate for on-chip gas sensor.

scholarly journals (1+1)-Dirac bound states in one dimension, with position-dependent Fermi velocity and mass

Open Physics ◽  
2013 ◽  
Vol 11 (4) ◽  
Author(s):  
Omar Mustafa
Keyword(s):  
Harmonic Oscillator ◽  
Bound States ◽  
Bound State ◽  
One Dimension ◽  
Fermi Velocity ◽  
Dirac Particles ◽  
The Continuum ◽  
Oscillator Models

AbstractWe extend Panella and Roy’s [17] work for massless Dirac particles with position-dependent (PD) velocity. We consider Dirac particles where the mass and velocity are both position-dependent. Bound states in the continuum (BIC)-like and discrete bound state solutions are reported. It is observed that BIC-like solutions are not only feasible for the ultra-relativistic (massless) Dirac particles but also for Dirac particles with PDmass and PD-velocity that satisfy the condition m(x) v F2 (x) = A, where A ≥ 0 is constant. Dirac Pöschl-Teller and harmonic oscillator models are also reported.

scholarly journals Second-harmonic generation enhancement in high-contrast micropillar AlGaAs resonator in bound states in the continuum regime

2021 ◽  
Vol 2015 (1) ◽  
pp. 012067
Author(s):  
Stanislav Kolodny ◽  
Valerii Kozin ◽  
Ivan Iorsh
Keyword(s):  
Numerical Modelling ◽  
Bound States ◽  
Second Harmonic ◽  
Local Fields ◽  
High Contrast ◽  
Specific Design ◽  
Resonant Enhancement ◽  
Shg Efficiency ◽  
Mode Volume ◽  
The Continuum

Abstract It has been shown that the use of micropillar resonators, which comprise a cylindrical semiconductor cavity sandwiched between the Bragg mirrors can substantially increase the quality factor preserving the mode volume, and thus substantially enhance the local fields. Here, we show that these structures indeed can facilitate the significant enhancement of the SHG efficiency. We provide a specific design of the AlGaAs pillar microcavity and use the numerical modelling to directly show the resonant enhancement of the SHG efficiency. We believe that the presented results would be of high interest to the nanophotonic community, especially in nonlinear optics field.

scholarly journals AUTOMATIC ESTIMATION OF SIZE PARAMETERS USING VERIFIED COMPUTERIZED STEREOANALYSIS

2011 ◽  
Vol 24 (1) ◽  
pp. 41 ◽  
Author(s):  
Peter R Mouton ◽  
Joel Durgavich ◽  
Donald K Ingram
Keyword(s):  
Biomedical Research ◽  
High Efficiency ◽  
Signal To Noise Ratio ◽  
Performance Testing ◽  
High Signal ◽  
High Contrast ◽  
Size Estimation ◽  
Labor Costs ◽  
Biological Objects ◽  
Novel Approach

State-of-the-art computerized stereology systems combine high-resolution video microscopy and hardwaresoftware integration with stereological methods to assist users in quantifying multidimensional parameters of importance to biomedical research, including volume, surface area, length, number, their variation and spatial distribution. The requirement for constant interactions between a trained, non-expert user and the targeted features of interest currently limits the throughput efficiency of these systems. To address this issue we developed a novel approach for automatic stereological analysis of 2-D images, Verified Computerized Stereoanalysis (VCS). The VCS approach minimizes the need for user interactions with high contrast [high signal-to-noise ratio (S:N)] biological objects of interest. Performance testing of the VCS approach confirmed dramatic increases in the efficiency of total object volume (size) estimation, without a loss of accuracy or precision compared to conventional computerized stereology. The broad application of high efficiency VCS to high-contrast biological objects on tissue sections could reduce labor costs, enhance hypothesis testing, and accelerate the progress of biomedical research focused on improvements in health and the management of disease.

scholarly journals Spectropolarimetry of low redshift Quasars: origin of the polarization and implications for black hole mass estimates.

2021 ◽  
Author(s):  
Alessandro Capetti ◽  
Ari Laor ◽  
Ranieri D Baldi ◽  
Andrew Robinson ◽  
Alessandro Marconi
Keyword(s):  
Black Hole ◽  
Line Width ◽  
Signal To Noise Ratio ◽  
Single Scattering ◽  
High Signal ◽  
Polarization Angle ◽  
Black Hole Mass ◽  
Scattering Medium ◽  
Line Region ◽  
The Continuum

Abstract We present the results of high signal-to-noise ratio VLT spectropolarimetry of a representative sample of 25 bright type 1 AGN at z < 0.37, of which nine are radio-loud. The sample covers uniformly the 5100 Å optical luminosity at L5100 ∼ 1044 − 1046 erg s−1, and Hα width at FWHM∼1000 − 10, 000 $\rm {\, km \, s}^{-1}$. We derive the continuum and the Hα polarization amplitude, polarization angle, and angle swing across the line, together with the radio properties. We find the following: 1. The broad line region (BLR) and continuum polarization are both produced by a single scattering medium. 2. The scattering medium is equatorial, and at right angle to the system axis. 3. The scattering medium is located at or just outside the BLR. The continuum polarization and the Hα polarization angle swing, can both serve as an inclination indicator. The observed line width is found to be affected by inclination, which can lead to an underestimate of the black hole mass by a factor of ∼5 for a close-to face-on view. The line width measured in the polarized flux overcomes the inclination bias, and provides a close-to equatorial view of the BLR in all AGN, which allows to reduce the inclination bias in the BLR based black hole mass estimates.

scholarly journals Bound states in the continuum in resonant nanostructures: an overview of engineered materials for tailored applications

Nanophotonics ◽  
2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Shereena Joseph ◽  
Saurabh Pandey ◽  
Swagato Sarkar ◽  
Joby Joseph
Keyword(s):  
Bound States ◽  
Beam Steering ◽  
Functional Materials ◽  
Bound State ◽  
Dielectric Medium ◽  
Quality Factors ◽  
Theoretical Frameworks ◽  
Experimental Realization ◽  
Promising Tool ◽  
The Continuum

Abstract From theoretical model to experimental realization, the bound state in the continuum (BIC) is an emerging area of research interest in the last decade. In the initial years, well-established theoretical frameworks explained the underlying physics for optical BIC modes excited in various symmetrical configurations. Eventually, in the last couple of years, optical-BICs were exploited as a promising tool for experimental realization with advanced nanofabrication techniques for numerous breakthrough applications. Here, we present a review of the evolution of BIC modes in various symmetry and functioning mediums along with their application. More specifically, depending upon the nature of the interacting medium, the excitations of BIC modes are classified into the pure dielectric and lossy plasmonic BICs. The dielectric constituents are again classified as photonic crystal functioning in the subwavelength regime, influenced by the diffraction modes and metasurfaces for interactions far from the diffraction regime. More importantly, engineered functional materials evolved with the pure dielectric medium are explored for hybrid-quasi-BIC modes with huge-quality factors, exhibiting a promising approach to trigger the nanoscale phenomena more efficiently. Similarly, hybrid modes instigated by the photonic and plasmonic constituents can replace the high dissipative losses of metallic components, sustaining the high localization of field and high figure of merit. Further, the discussions are based on the applications of the localized BIC modes and high-quality quasi-BIC resonance traits in the nonlinear harmonic generation, refractometric sensing, imaging, lasing, nanocavities, low loss on-chip communication, and as a photodetector. The topology-controlled beam steering and, chiral sensing has also been briefly discussed.

scholarly journals Ionization-driven intrinsic absorption line variability of BAL quasars in the Stripe 82 region

2019 ◽  
Vol 486 (2) ◽  
pp. 2379-2396 ◽  
Author(s):  
M Vivek
Keyword(s):  
Absorption Line ◽  
Signal To Noise Ratio ◽  
Sloan Digital Sky Survey ◽  
High Signal ◽  
Broad Absorption Line ◽  
Final Sample ◽  
Sky Survey ◽  
Saturation Effects ◽  
The Continuum

Abstract We investigate the connection between the intrinsic C iv absorption line variability and the continuum flux changes of broad absorption line (BAL) quasars using a sample of 78 sources in the Stripe 82 region. The absorption trough variability parameters are measured using the archival multi-epoch spectroscopic data from the Sloan Digital Sky Survey (SDSS), and the continuum flux variability parameters are estimated from the photometric light curves obtained by the SDSS and the Catalina Real-Time Survey surveys. We find evidence for weak correlations (ρs ∼ 0.3) between the intrinsic C iv absorption line variability and the quasar continuum variability for the final sample of 78 BAL quasars. The correlation strengths improve (ρs ∼ 0.5) for the ‘high-signal-to-noise ratio (SNR)’ sample sources that have higher spectral SNR. Using two subsets of the high-SNR sample differing on the absorption trough depth, we find that the shallow-trough subset shows an even stronger correlation (ρs ∼ 0.6), whereas the deep-trough subset does not show any correlation between the absorption line variability and the continuum variability. These results point to the important role of saturation effects in the correlation between the absorption line variability and the continuum variability of BAL quasars. Considering other effects that can also smear the correlation, we conclude that the actual correlation between the absorption line and continuum variability is even stronger.

Ultra-compact organic vertical-cavity laser with high-contrast grating feedback for gas detection

2020 ◽  
pp. 1-1
Author(s):  
Zhilei Deng ◽  
Jiacheng Sun ◽  
Haoran Zhang ◽  
Israel De Leon ◽  
Remo Proietti Zaccaria ◽  
...  
Keyword(s):  
Gas Detection ◽  
High Contrast ◽  
High Contrast Grating ◽  
Cavity Laser ◽  
Vertical Cavity

scholarly journals The GALAH survey: characterization of emission-line stars with spectral modelling using autoencoders

2020 ◽  
Vol 500 (4) ◽  
pp. 4849-4865
Author(s):  
Klemen Čotar ◽  
Tomaž Zwitter ◽  
Gregor Traven ◽  
Joss Bland-Hawthorn ◽  
Sven Buder ◽  
...  
Keyword(s):  
Emission Line ◽  
Rarefied Gas ◽  
Signal To Noise Ratio ◽  
Emission Spectra ◽  
High Signal ◽  
Physical Mechanisms ◽  
Repeated Observation ◽  
Hα Emission ◽  
The Continuum

ABSTRACT We present a neural network autoencoder structure that is able to extract essential latent spectral features from observed spectra and then reconstruct a spectrum from those features. Because of the training with a set of unpeculiar spectra, the network is able to reproduce a spectrum of high signal-to-noise ratio that does not show any spectral peculiarities, even if they are present in an observed spectrum. Spectra generated in this manner were used to identify various emission features among spectra acquired by multiple surveys using the HERMES spectrograph at the Anglo-Australian telescope. Emission features were identified by a direct comparison of the observed and generated spectra. Using the described comparison procedure, we discovered 10 364 candidate spectra with varying intensities (from partially filled-in to well above the continuum) of the Hα/Hβ emission component, produced by different physical mechanisms. A fraction of these spectra belong to the repeated observation that shows temporal variability in their emission profile. Among the emission spectra, we find objects that feature contributions from a nearby rarefied gas (identified through the emission of [N ii] and [S ii] lines) that was identified in 4004 spectra, which were not all identified as having Hα emission. The positions of identified emission-line objects coincide with multiple known regions that harbour young stars. Similarly, detected nebular emission spectra coincide with visually prominent nebular clouds observable in the red all-sky photographic composites.

Tunable plasmonic bound states in the continuum in the visible range

2021 ◽  
Vol 103 (4) ◽  
Author(s):  
Shuoyan Sun ◽  
Yufeng Ding ◽  
Haozhi Li ◽  
Peng Hu ◽  
Chang-Wei Cheng ◽  
...  
Keyword(s):  
Bound States ◽  
Visible Range ◽  
The Continuum
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