Narrow Dip Research Articles

Erratum: Narrow dip inside a natural linewidth absorption profile in a system of two atoms [Phys. Rev. A 92 , 053840 (2015)

Erratum: Narrow dip inside a natural linewidth absorption profile in a system of two atoms [Phys. Rev. A <b>92</b> , 053840 (2015)

Design Analysis of Refractive Index Sensor with High Quality Factor Using Au-Al2O3 Grating on Aluminum

We propose a surface plasmon resonance (SPR)-based refractive index sensor using gold-alumina grating over aluminum film for biosensing. Conventional SPR sensor based on gold grating exhibits broader SPR dips whereas that based on aluminum grating exhibits narrow reflection dip. A narrow reflection dip is desirable as it provides good resolution and improves the accuracy of measurement. Aluminum is less stable and generally is not preferred for an SPR-based sensor. It is more prone to being oxidized, which reduces the sensitivity and increases the width of the reflection dip of the sensor. While gold cannot provide narrow SPR reflection dips, but is used as an SPR active metal due to its more chemical stability. In order to improve the accuracy of gold grating-based sensor while taking care of oxidation problem of aluminum, in this paper, we propose a gold grating over aluminum film for SPR-based sensor and show that this configuration improves the sensitivity and the detection accuracy of the conventional sensor. Moreover, the oxidation problem is reduced to some extent as a part of aluminum is covered with gold. In order to completely avoid the oxidation of aluminum, we further propose to cover the exposed part of the aluminum with alumina and show that this configuration further improves the accuracy by reducing the width of the SPR reflection dip without affecting the sensitivity significantly. Numerical simulations show that sensitivity of proposed sensor is 270.33°/RIU with quality factor of more than 267.65 RIU−1.

Спектроскопия плазмон-экситонов в наноструктурах полупроводник-металл

AbstractThe results of the theory considering mixed plasmon-excitonic modes and their spectroscopy are presented. The plasmon-excitons are formed owing to strong Coulomb coupling between quasi-two-dimensional excitons of a quantum well and dipole plasmons of nanoparticles. The effective polarizability associated with a nanoparticle is calculated in a self-consistent approximation taking into account the local field determined by in-layer dipole plasmons and their image charges due to the excitonic polarization of a near quantum well. The spectra of elastic scattering and specular reflection of light are investigated in cases of a single silver nanoparticle and a monolayer of such particles situated in close proximity to a quantum well GaAs/AlGaAs. The optical spectra show a two-peak structure with a deep and narrow dip in the resonant range of plasmon-excitons. Propagation of plasmon-excitonic polaritons is discussed for periodic superlattices whose unit cell consists of a quantum well and a layer of metal nanoparticles. The superradiance regime originating in the Bragg diffraction of plasmon-excitonic polaritons by the superlattice is investigated. It is shown that the broad spectrum of plasmonic reflection depending on the number of unit cells in a superlattice also has a narrow dip at the exciton frequency.

Decade long RXTE monitoring observations of Be/X-ray binary pulsar EXO 2030+375

We present a comprehensive timing and spectral studies of Be/X-ray binary pulsar EXO 2030+375 using extensive Rossi X-ray Timing Explorer observations from 1995 till 2011, covering numerous Type I and 2006 Type II outbursts. Pulse profiles of the pulsar were found to be strongly luminosity dependent. At low luminosity, the pulse profile consisted of a main peak and a minor peak that evolved into a broad structure at high luminosity with a significant phase shift. A narrow and sharp absorption dip, also dependent on energy and luminosity, was detected in the pulse profile. Comparison of pulse profiles showed that the features at a particular luminosity are independent of type of X-ray outbursts. This indicates that the emission geometry is solely a function of mass accretion rate. The broadband energy spectrum was described with a partial covering high energy cutoff model as well as a physical model based on thermal and bulk Comptonization in accretion column. We did not find any signature of cyclotron resonance scattering feature in the spectra obtained from all the observations. A detailed analysis of spectral parameters showed that, depending on source luminosity, the power-law photon index was distributed in three distinct regions. It suggests the phases of spectral transition from sub-critical to super-critical regimes in the pulsar as proposed theoretically. A region with constant photon index was also observed in ~(2-4) x 10^37 erg/s range, indicating critical luminosity regime in EXO 2030+375.

Fano resonances in a photonic crystal covered with a perforated gold film and its application to bio-sensing

Optical properties of the photonic crystal covered with a perforated metal film were investigated and the existence of the Fano-type resonances was shown. The Fano resonances originate from the interaction between the optical Tamm state and the waveguide modes of the photonic crystal. It manifests itself as a narrow dip in a broad peak in the transmission spectrum related to the optical Tamm state. The design of a sensor based on this Fano resonance that is sensitive to the change of the environment refractive index is suggested.

Investigation of Er doped zinc borate glasses by low-temperature photoluminescence

Er3+ doped (95-x)B2O3-xZnO-5TiO2 (x = 45, 50 and 55mol%) bulk glasses were prepared by conventional melt quenching method and investigated by transmission and photoluminescence (PL) spectroscopy. Transmission spectra exhibit sharp absorption bands at 364, 377, 406, 441, 448, 488, 521, 541, 651, 792, 974, and 1530nm, that correspond to absorption on Er3+ ions and they are attributed to the optical transitions from the ground state 4I15/2 to the excited states 4G9/2, 4G11/2,4F9/2, 4F3/2, 4F5/2, 4F7/2, 2H11/2, 4S3/2, 4F9/2, 4I9/2, 4I11/2 and 4I13/2, respectively. The optical gap has been estimated around 3.5eV with a tendency to increase with increasing ZnO content. Low-temperature PL properties of the Er3+ doped glasses and of the host glass itself were investigated. To achieve this goal, two different wavelengths (325 and 514.5nm) were used for PL excitation. PL spectra excited by He-Cd laser at 325nm were dominated by the host glass broad-band luminescence centred at around 570nm. Simultaneously we observed narrow emission and absorption features due to 4f-4f electronic transitions in Er3+ ions superposed on the broad band host glass luminescence. We argue that these superposed narrow absorption dips represent a direct evidence of the energy transfer from the electronic structure of the host to 4f states of Er3+ ions. Fine structure of Er3+ emission bands at 980 and 1530nm, corresponding to radiative transitions from the two lowest excited states of Er3+ ions to the ground state manifold have been investigated at room temperature and at 4K, and a schematic energy diagram of Stark levels of 4I11/2, 4I13/2 and 4I15/2 manifolds has been deduced.

Plasmon-excitonic polaritons in superlattices

A theory for propagation of polaritons in superlattices with resonant plasmon-exciton coupling is presented. A periodical superlattice consists of a finite number of cells with closely located a quantum well and a monolayer of metal nanoparticles. Under study is the spectrum of hybrid modes formed of the quasitwo- dimensional excitons of quantum wells and the dipole plasmons of metal particles. The problem of electrodynamics is solved by the method of Green’s functions with taking account of the resonant polarization of quantum wells and nanoparticles in a self-consistent approximation. The effective polarizability of spheroidal particles occupying a square lattice is calculated with taking into consideration the local-field effect of dipole plasmons of the layer and their images caused by the excitonic polarization of nearest quantum well. Optical reflection spectra of superlattices with GaAs/AlGaAs quantum wells and silver particles are numerically analyzed. Special attention is paid to the superradiant regime originated in the Bragg diffraction of polaritons in superlattice. Superradiance is investigated separately for plasmons and excitons, and then for hybrid plasmonexcitonic polaritons. It is demonstrated that the broad spectrum of reflectance associated with plasmons depends on the number of cells in superlattice, and it has a narrow spectral dip in the range of plasmon-excitonic Rabi splitting.

Orbiting Clouds of Material at the Keplerian Co-rotation Radius of Rapidly Rotating Low-mass WTTs in Upper Sco

Abstract Using K2 data, we identified 23 very-low-mass members of the ρ Oph and Upper Scorpius star-forming region as having periodic photometric variability not easily explained by well-established physical mechanisms such as star spots, eclipsing binaries, or pulsation. All of these unusual stars are mid-to-late M dwarfs without evidence of active accretion, and with photometric periods generally &lt;1 day. Often the unusual light-curve signature takes the form of narrow flux dips; when we also have rotation periods from star spots, the two periods agree, suggesting that the flux dips are due to material orbiting the star at the Keplerian co-rotation radius. We sometimes see “state-changes” in the phased light-curve morphologies where ∼25% of the waveform changes shape on timescales less than a day; often, the “state-change” takes place immediately after a strong flare. For the group of stars with these sudden light-curve morphology shifts, we attribute their flux dips as most probably arising from eclipses of warm coronal gas clouds, analagous to the slingshot prominences postulated to explain transient Hα absorption features in AB Doradus and other rapidly rotating late-type stars. For another group of stars with somewhat longer periods, we find the short-duration flux dips to be highly variable on both short and long timescales, with generally asymmetric flux-dip profiles. We believe that these flux dips are due to particulate clouds possibly associated with a close-in planet or resulting from a recent collisional event.

Effects of Zb states and bottom meson loops on ϒ(4S)→ϒ(1S,2S)π+π− transitions

We study the dipion transitions $\Upsilon(4S) \rightarrow \Upsilon(nS) \pi^+\pi^-$ $(n=1,2)$. In particular, we consider the effects of the two intermediate bottomoniumlike exotic states $Z_b(10610)$ and $Z_b(10650)$ as well as bottom meson loops. The strong pion-pion final-state interactions, especially including channel coupling to $K\bar{K}$ in the $S$-wave, are taken into account model-independently by using dispersion theory. Based on a nonrelativistic effective field theory we find that the contribution from the bottom meson loops is comparable to those from the chiral contact terms and the $Z_b$-exchange terms. For the $\Upsilon(4S) \rightarrow \Upsilon(2S) \pi^+\pi^-$ decay, the result shows that including the effects of the $Z_b$-exchange and the bottom meson loops can naturally reproduce the two-hump behavior of the $\pi\pi$ mass spectra. Future angular distribution data are decisive for the identification of different production mechanisms. For the $\Upsilon(4S) \rightarrow \Upsilon(1S) \pi^+\pi^-$ decay, we show that there is a narrow dip around 1 GeV in the $\pi\pi$ invariant mass distribution, caused by the final-state interactions. The distribution is clearly different from that in similar transitions from lower $\Upsilon$ states, and needs to be verified by future data with high statistics. Also we predict the decay width and the dikaon mass distribution of the $\Upsilon(4S) \rightarrow \Upsilon(1S) K^+ K^-$ process.

3D printed hollow core terahertz Bragg waveguides with defect layers for surface sensing applications.

We study a 3D-printed hollow core terahertz (THz) Bragg waveguide for resonant surface sensing applications. We demonstrate theoretically and confirm experimentally that by introducing a defect in the first layer of the Bragg reflector, thereby causing anticrossing between the dispersion relations of the core-guided mode and the defect mode, we can create a sharp transmission dip in the waveguide transmission spectrum. By tracking changes in the spectral position of the narrow transmission dip, one can build a sensor, which is highly sensitive to the optical properties of the defect layer. To calibrate our sensor, we use PMMA layers of various thicknesses deposited onto the waveguide core surface. The measured sensitivity to changes in the defect layer thickness is found to be 0.1 GHz/μm. Then, we explore THz resonant surface sensing using α-lactose monohydrate powder as an analyte. We employ a rotating THz Bragg fiber and a semi-automatic powder feeder to explore the limit of the analyte thickness detection using a surface modality. We demonstrate experimentally that powder layer thickness variations as small as 3μm can be reliably detected with our sensor. Finally, we present a comparative study of the time-domain spectroscopy versus continuous wave THz systems supplemented with THz imaging for resonant surface sensing applications.

Various Barbs in Solar Filaments

AbstractInterest to lateral details of the solar filament shape named barbs, motivated by their relationship to filament chirality and helicity, showed their different orientation relative to the expected direction of the magnetic field. While the majority of barbs are stretched along the field, some barbs seem to be transversal to it and are referred to as anomalous barbs. We analyse the deformation of helical field lines by a small parasitic polarity using a simple flux rope model with a force-free field. A rather small and distant source of parasitic polarity stretches the bottom parts of the helical lines in its direction creating a lateral extension of dips below the flux-rope axis. They can be considered as normal barbs of the filament. A stronger and closer source of parasitic polarity makes the flux-rope field lines to be convex below its axis and creates narrow and deep dips near its position. As a result, the narrow structure, with thin threads across it, is formed whose axis is nearly perpendicular to the field. The structure resembles an anomalous barb. Hence, the presence of anomalous barbs does not contradict the flux-rope structure of a filament.

Lattice plasmons in dielectric nanoparticle arrays arranged on metal film

We propose a hybrid plasmonic photonic crystal consisting of a square array of dielectric nanoparticles arranged on a metal film with a gap inbetween. Simulations show that this plasmonic crystal supports lattice plasmon modes just like the metal nanoparticle array, exhibiting an extremely narrow and deep reflection dip. When interparticle spacing increases from 800 to 1000 nm, the full width at half the maximum of lattice plasmons decreases from 21 to 4 nm, and the lowest reflectance is close to zero. The resonant wavelength of this plasmonic crystal is highly sensitive to the local environment. It yields a sensitivity of 700 nm RIU−1 and a figure of merit of 33, which can be used in sensing of the refractive index.

Erratum: Narrow dip inside a natural linewidth absorption profile in a system of two atoms [Phys. Rev. A92, 053840 (2015)

Erratum: Narrow dip inside a natural linewidth absorption profile in a system of two atoms [Phys. Rev. A92, 053840 (2015)

Phase-dependent multiple optomechanically induced absorption in multimode optomechanical systems with mechanical driving

We investigate theoretically the response of the output field from an optomechanical system consisting of $N$ nearly degenerate mechanical resonators each coupled to a common cavity mode. When the cavity is driven simultaneously by a strong control field and a weak probe field and each mechanical resonator is driven by a coherent mechanical pump, we obtain the analytical expression for the probe transmission. We show that the probe transmission spectrum can exhibit multiple optomechanically induced absorption (OMIA) with at most $N$ narrow absorption dips, which can be tuned by the phase and amplitude of the mechanical driving field as well as the control field. Moreover, it is shown that the peak probe transmission can be enhanced or suppressed by increasing the amplitude of the mechanical pump, which depends on the phase difference. This phase-dependent effect plays an important role in controlling the propagation of the probe field between OMIA and parametric amplification.

Sensing Application in Fano Resonance With T-Shape Structure

A T-shape plasmonic structure, consisting of a stub resonator coupled with bus waveguide and cavity, has been investigated numerically and theoretically. Due to the near-field coupling mechanism between bright and dark modes, plasmon induced transparency can be observed in transmission spectrum. Moreover, it is demonstrated theoretically that the first order resonance mode can exist or not in the cavity by adjusting lateral displacement ( S ), which leads to the appearance or disappearance of the narrow transmission dip together with a steep Fano resonance in reflection spectrum. The effects of different parameters on a figure of merit (FOM) are investigated in detail. In sensing applications, the T-shape structure yields a sensitivity of ∼1090 nm shift per refractive index unit and a FOM of 33340. The results indicate that the width of cavity ( w c) is more sensitive than the distance ( g ) and length ( L ) for FOM. The transparency and Fano resonance effects may have potential applications in optical switch, slow-light devices, and nano sensor in highly integrated optical circuits.

Narrow dip inside a natural linewidth absorption profile in a system of two atoms

Absorption spectrum of a system of two closely spaced identical atoms displays, at certain preparation, a dip that can be much narrower than the natural linewidth. This preparation includes (i) application of a strong magnetic field at an angle $\ensuremath{\alpha}$, that is very close to the magic angle ${\ensuremath{\alpha}}_{0}=arccos(1/\sqrt{3})\ensuremath{\approx}{54.7}^{\ensuremath{\circ}}$, with respect to the direction from one atom to another, and (ii) in-plane illumination by a laser light in the form of a nonresonant standing wave polarized at the same angle $\ensuremath{\alpha}$. Both qualitative and quantitative arguments for the narrow dip effect are presented.

Is 4U 0114+65 an eclipsing HMXB?

We present the pulsation and spectral characteristics of the HMXB 4U 0114+65 during a \emph{Suzaku} observation covering the part of the orbit that included the previously known low intensity emission of the source (dip) and the egress from this state. This dip has been interpreted in previous works as an X-ray eclipse. Notably, in this Suzaku observation, the count rate during and outside the dip vary by a factor of only 2-4 at odds with the eclipses of other HMXBs, where the intensity drops upto two orders of magnitude. The orbital intensity profile of 4U 0114+65 is characterized by a narrow dip in the RXTE-ASM (2-12 \rm{keV}) light curve and a shallower one in the Swift-BAT (15-50 \rm{keV}), which is different from eclipse ingress/egress behaviour of other HMXBs. The time-resolved spectral analysis reveal moderate absorption column density (N$_{H}$ - 2-20 $\times$ $10^{22}$ atoms $cm^{-2}$) and a relatively low equivalent width ($\sim$ 30 \rm{eV} \& 12 \rm{eV} of the iron K$_\alpha$ and K$_\beta$ lines respectively) as opposed to the typical X-ray spectra of HMXBs during eclipse where the equivalent width is $\sim$ 1 \rm{keV}. Both XIS and PIN data show clear pulsations during the dip, which we have further confirmed using the entire archival data of the IBIS/ISGRI and JEM-X instruments onboard \emph{INTEGRAL}. The results we presented question the previous interpretation of the dip in the light curve of 4U 0114+65 as an X-ray eclipse. We thus discuss alternative interpretations of the periodic dip in the light curve of 4U 0114+65.

Critical-angle-based sensor with improved figure of merit using dip detection.

It is demonstrated theoretically and experimentally that a one-dimensional photonic crystal (1D-PC) made of quarter waves stacked on top of a prism exhibits both TE and TM resonances that coincide with the critical angle θ(c) when the 1D-PC is semi-infinite and with very little deviation from θ(c) for a finite 1D-PC. As a refractive index (RI) sensor, it behaves as a total internal reflection sensor at θ(c) with the advantage of detecting a narrow dip rather than an edge and enhanced figure of merit by increasing the number of periods in the 1D-PC. Using the diverging beam approach on an optical bench, a two channel sensor is demonstrated with a sensitivity of 120.9 deg/RIU and a detection limit of 1.9×10(-5) RIU.

Ballistic transport in nanowires through non-magnetic or magnetic cavity

Ballistic transport phenomena through a region containing a cavity in a quasi-one-dimensional quantum nanowire are investigated. Conductance curves calculated as a function of a structural parameter show quantum interference effects on transport clearly. In a special geometry, very narrow periodic dips, which are attributable to the anti-resonance, appear on the conductance curve. The nature of the virtual bound state resulting in the anti-resonance is studied in detail. Electron conductions through a small dilute magnetic semiconductor are also investigated.

Tunable dynamic Fano resonances in coupled-resonator optical waveguides

A route toward line-shape engineering of Fano resonances in photonic structures is theoretically proposed, which uses dynamic modulation of the refractive index of a microcavity. The method is exemplified by considering coupled-resonator optical waveguide systems. An exact Floquet analysis, based on coupled-mode theory, is presented. Two distinct kinds of resonances can be dynamically created, depending on whether or not the static structure sustains a localized mode. In the former case, a single Fano resonance arises, which can be tuned in both frequency and linewidth by varying the refractive index modulation amplitude and frequency. In the latter case, two resonances, in the form of narrow asymmetric dips in the transmittance, are found, which can overlap resulting in an electromagnetically induced transparency effect.