Resonance Absorption Lines Research Articles

Strongly coupled plasmon-exciton polaritons for photobleaching suppression.

Strong light-matter interactions have received a lot of attention, for example in the pursuit of plasmonic-excitonic structures as coherent light sources with low-power threshold. In this study, we investigate the influence of room temperature strong coupling between surface plasmon polaritons (SPP) and excitons on fluorescence lifetimes and photobleaching effects. Our plasmonic-photonic structure, comprising of thin silver (Ag) and gold (Au) layers with a Rhodamine 6G (R6G) dye layer, shows a clear shift in the plasmon resonance and R6G absorption lines with varying incident angles, indicative of strong coupling, with a measured Rabi splitting of approximately 90 meV. Fluorescence lifetime imaging microscopy (FLIM) was then employed to assess photobleaching, revealing a significant reduction in photobleaching effect for in strongly coupled plasmonic-excitonic structures compared to single Rhodamine R6G layers. Our findings indicate the pivotal role of strong light-matter interactions in reducing photobleaching effects and stabilizing fluorescence intensities, offering promising avenues for developing quantum multiparticle nanophotonic devices with enhanced stability and performance.

A search for the missing baryons with X-ray absorption lines towards the blazar 1ES 1553+113

ABSTRACT This paper presents an analysis of XMM–Newton and Chandra X-ray spectra of the quasar 1ES 1553+113, in search for absorption lines from the intervening warm–hot intergalactic medium (WHIM). A search for O vii, O viii, and Ne ix resonance absorption lines was performed at eight fixed redshifts that feature O vi or H i broad Lyman α absorption lines that were previously detected from Hubble Space Telescope (HST) data. The search yielded one possible detection of O vii at a redshift z ≃ 0.1877 with an O vi prior, with a statistical significance that is equivalent to a 2.6σ confidence level. The spectra were also stacked at the wavelengths of the expected redshifted O vii and O viii lines, but the analysis did not reveal evidence for the presence of additional X-ray absorbing WHIM. Moreover, the spectra were used to investigate two putative O vii absorption lines that were detected serendipitously in an earlier analysis of the same data by F. Nicastro and collaborators. The paper also presents a comprehensive statistical framework for cosmological inferences from the analysis of absorption lines, which makes use of cosmological simulations for the joint probability distributions of far-ultraviolet (FUV) and X-ray ions. Accordingly, we conclude that the new possible O vii absorption at z ≃ 0.1877 is consistent with a contribution from the hot WHIM to the baryon density in an amount of ΩWHIM, X/Ωb = 44 ± 22 per cent. However, there are large systematic uncertainties associated with the temperature and abundances of the absorbers, and only a larger sample of X-ray sources can provide an accurate determination of the cosmological density of the WHIM.

Frequency Locking of the Titanium–Sapphire Laser by Resonant Absorption Lines of a Cesium-Vapor Cell in a Cavity

Frequency Locking of the Titanium–Sapphire Laser by Resonant Absorption Lines of a Cesium-Vapor Cell in a Cavity

The water vapor self-continuum absorption at room temperature in the 1.25 µm window

The water vapor self-continuum is newly measured at room temperature in the high energy edge of the 1.25 µm window by using highly stable and sensitive cavity ring down spectroscopy (CRDS). Self-continuum cross-sections, CS, are derived between 8290 and 8620 cm−1 at 29 selected spectral points by using pressure ramps (up to 15 Torr) of pure water vapor. Purely quadratic pressure dependence is obtained for the absorption coefficient at each measurement point. Although the spectral measurement points were chosen to minimize the contribution of resonance line absorption, the latter represents between 30 and 70% of the measured absorption in the studied region. The measurements are found consistent with a previous study of the low frequency edge of the 1.25 µm windows and (Campargue et al. J Geophys Res Atmos 2016;121:13,180 – 13,203. doi:10.1002/2016JD025531). The frequency dependence of the retrieved CS values shows an overall good agreement with the MT_CKD values, although an additional broad absorption feature is observed with a center near 8455 cm−1. It is tentatively interpreted as a possible impact of the uncertainties on the resonance line contribution on the derived CS values or as a possible evidence of a band of the bound dimers, (H2O)2.

Development of lidar for remote methane sensing using an optimal configuration of high-power laser diodes

A broadband differential absorption lidar (DIAL) is developed making us of the properties of high-power pulsed laser diodes for the purpose of monitoring methane, a major atmospheric greenhouse biogas. The detection range is optimized for the CH4 Q-branch 2v3 overtone spectrum centered at 1.667 μm and mixed with water-vapor absorption bands of. The resonance absorption evaluated of the DIAL signal is an integral sum of the multiple CH4 resonance absorption lines modulating the characteristic broad laser line and simultaneously compensating the interfering water-vapor absorption. A compact DIAL scheme is developed using an optimal configuration of high-power laser diodes matching the selected spectral parameters.

Bistable absorption in a 1D photonic crystal with a nanocomposite defect layer.

We investigate the nonlinear absorption properties of a defective one-dimensional photonic crystal at the near-infrared range using the nonlinear transfer matrix method. The defect is a nanocomposite layer containing vanadium dioxide nanoparticles sandwiched between two nonlinear dielectric layers. The linear absorption spectrum of the designed structure has three resonant absorption lines at the bandgap region of the photonic crystal. We can reconfigure the structure in the linear regime from nearly transparent to absorbent or vice versa in multiple resonant wavelengths by adjusting the temperature. Moreover, the system shows absorptive bistability by adjusting the intensity and incident angle of the input light. We discuss the tunability of the nonlinear absorption in detail. In the nonlinear regime, we show that, besides the temperature, the structure can be reconfigured from absorbent to transparent and vice versa by adjusting the incident optical power and the incident angle. We validate the results by examining the electric field distribution throughout the structure.

Many-Electron System on Helium and Color Center Spectroscopy.

Electrons on the helium surface display sharp resonant absorption lines related to the transitions between the subbands of quantized motion transverse to the surface. A magnetic field parallel to the surface strongly affects the absorption spectrum. We show that the effect results from admixing the intersubband transitions to the in-plane quantum dynamics of the strongly correlated electron liquid or a Wigner crystal. This is similar to the admixing of electron transitions in color centers to phonons. The spectrum permits a direct characterization of the many-electron dynamics and also enables testing the theory of color centers in a system with controllable coupling.

Raman spectrometer for high precision temperature sensing of atmospheric gases.

We present a highly accurate Raman spectrometer capable of measuring changes in atmospheric temperature as small as 0.75 K with high spatial and temporal resolution. The spectrometer is based on a laser diode tuned to the resonant absorption line of the 85Rb isotope near 780.0 nm. A heated glass cell containing Rb atoms was used as an ultranarrowband atomic absorption notch filter with 0.3cm-1 bandwidth and optical density as high as four. This filter was placed in front of the spectrograph and blocked up to 99.99% of the elastically scattered laser light, which made it possible to resolve the pure-rotational Raman spectra of molecular atmospheric gases. The relative intensities of pure-rotational Raman transitions were then used to infer atmospheric temperature changes.

The influence of clouds on atmospheric radiation fluctuations in the resonance absorption band of water vapor 18 27.2 GHz

The results of processing new experimental data on brightness temperature of atmospheric downwelling radiation near the resonance absorption line of water vapor 22.235 GHz are presented. The experiment was carried out by means of special 47-channel microwave radiometer-spectrometer. In this article the observations of stable clear sky and also cumulus cloud cover of various vertical extent for summer 2018-2019 measurement periods are considered. Due to assess the dynamics of brightness temperature fluctuations, the apparatus of Kolmogorov’s structural functions is used. Spectra of square root of structural function for wide range of temporal interval values under clear sky and cumulus cloud cover conditions are obtained. The two-frequency method of integral atmospheric moisture content evaluation is discussed. Experimental dependencies of cloud liquid water content on square root of structural function are shown.

Terahertz-infrared electrodynamics of single-crystalline Ba0.2Pb0.8Al1.2Fe10.8O19 M-type hexaferrite

Spectral response of single-crystalline Ba0.2Pb0.8Al1.2Fe10.8O19 synthesized by a modified Czochralski method is investigated using terahertz-infrared spectroscopy. Reflectivity, transmissivity, and complex dielectric permittivity spectra of the compound are studied in the temperature range from 6 to 300 K and in the frequency interval 8-8000 cm−1 for two principle polarizations of the radiation electric field relative to the crystallographic c-axis, namely E||c and E⊥c. The resonance absorption lines observed above 80 cm−1 are assigned to polar lattice vibrations basing on a factor group analysis and a comparison with a dielectric response of isostructural compounds. A set of absorption bands is observed in a range of 8–80 cm−1. To clarify their nature, a model is developed that considers electronic transitions within the fine-structured ground state of four-fold coordinated Fe2+. It is shown that the trigonal distortions of the crystal field lead to lowering of the symmetry of 4f1 and 4e tetrahedral site-positions of Fe2+ and, as a result, to further splitting of the ground state spin-orbital sub-levels. Electro-dipole transitions between the corresponding sub-levels are associated with the absorption lines observed in a low-energy response (at 8-80 cm−1) of the Ba0.2Pb0.8Al1.2Fe10.8O19 compound. The study paves the way for the development of low cost materials with high dielectric permittivity (about 30) at terahertz frequencies that are promising for the manufacture of electronic devices with enhanced characteristics.

Theoretical basis of optical engineering of ultrathin crystalline film-structures

Based on microscopic (exciton) theory of optical properties of perturbed ultrathin molecular films, the absorption, reflection, and transparency indices were formulated and presented in dependence on frequencies of an external electromagnetic field in near IR region. It has been shown that all optical properties depend on the position of the crystal plane with regard to boundary planes of the film. We have determined and analyzed optical properties relations for the whole film structure based on the consideration for multiple reflection, absorption, and transparency in observed multilayered structure. The four-layered dielectric nanofilms with different boundary conditions on surfaces were analyzed and some discrete resonant absorption lines were obtained. Their number, position, and distribution depend on the boundary parameter values, i.e. on the type and the technological process of their preparation/fabrication. Practically monochromatic absorption may occur. Unlike the corresponding bulk-samples, which are total absorbers throughout the near IR, region, in ultrathin films will appear selective and discrete reflection and transparency. These results could provide a great contribution to optical engineering of nanostructures, especially in technology of designing of new electronic and photonic equipment, and for nanoparticles construction for drug carrier/delivery in nanomedicine.

A Systematic Study of Galactic Outflows via Fluorescence Emission: Implications for Their Size and Structure

Abstract Galactic outflows play a major role in the evolution of galaxies, but the underlying physical processes are poorly understood. This is mainly because we have little information about the outflow structure, especially on large scales. In this paper, we probe the structure of galactic outflows in low-z starbursts using a combination of ultraviolet spectroscopy and imaging of the fluorescence emission lines (associated with transitions to excited fine-structure levels) and spectroscopy of the corresponding strongly blueshifted resonance absorption lines. We find that, in the majority of cases, the observed fluorescence emission lines are much weaker and narrower than the absorption lines, originating in the star-forming interstellar medium and/or the slowest-moving part of the inner outflow. In a minority of cases, the outflowing absorbing material does make a significant contribution to the fluorescence emission. These latter systems are characterized by both strong Lyα emission lines and weak low-ionization absorption lines (both known to be empirical signs of Lyman-continuum leakage). We argue that the observed weakness of emission from the outflow seen in the majority of cases is due to the missing emission arising on scales larger than those encompassed by the aperture of the Cosmic Origins Spectrograph on board the Hubble Space Telescope. This implies shallow radial density profiles in these outflows, and suggests that most of the observed absorbing material must be created/injected at radii much larger than that of the starburst. This has important implications both for our understanding of the physics of galactic outflows and for our estimation of their principal properties.

Ion Cyclotron Resonant Absorption Lines in ELF Hiss Power Spectral Density in the Low‐Latitude Ionosphere

AbstractThe effects of multiple ion species have been observed in electromagnetic wave spectra in both the ionosphere and the magnetosphere. Here we report an event from Communication/Navigation Outage Forecast System satellite, showing a new imprint of various ion species in observations of extremely low frequency (ELF) hiss wave spectra near the equatorial ionosphere, which presents minima in the power spectral density at gyrofrequencies and their harmonics of multiple ion species (e.g., O and He ). Cyclotron harmonic resonant absorption is proposed to account for the observed spectral and polarization properties. Furthermore, the implication of using those wave power spectral minima to identify minor ion species in the ionosphere is discussed.

Delithiated Fe1-xMgxPO4 cathode materials: Structural, magnetic, and Mössbauer studies

Fe1-xMgxPO4 (x = 0.01, 0.05, and 0.1) cathode materials are synthesized by a two-step method, which combines the solid-state reaction method and the chemical lithium deintercalation method. A study was conducted to investigate the structural and the magnetic properties of Fe1-xMgxPO4. The crystalline structure of the samples was analyzed by X-ray diffractometer (XRD) using the Rietveld refinement. The magnetic properties of the samples were determined from vibrating sample magnetometer (VSM) and Mösssbauer spectroscopy, including their magnetic interactions, Fe ion states, and structural ordering. The Néel temperature (TN) of Fe1-xMgxPO4 decreases with the increase of the Mg content due to the weakening of the antiferromagnetic exchange. Furthermore, for Fe1-xMgxPO4, the effective moment value decreases as expected with increasing Mg content. Mössbauer spectroscopy measurements at different temperatures were made. The spectrum at 295 K was fitted with a doublet, which has an isomer shift of δ = 0.32 – 0.43 mm/s (Fe3+). The large value of the electric quadrupole splitting (∆EQ = 0.95 – 1.87 mm/s) is explained by the asymmetric local environment of the Fe ions. Below the TN, the spectra of Fe1-xMgxPO4 in the eight resonance absorption lines (including two relatively small intensities) were analyzed. We can obtain a spin value for Fe ions (S = 5/2) of Fe0.9Mg0.1PO4 from the Brillouin functional analysis.

Effect of Structural Inhomogeneities on the Spin-Wave and Magnetic Properties of Monocrystalline Spinel Ferrite Films in the Microwave Range

We have studied magnetic parameters of monocrystalline manganese spinel ferrite films differing in composition and structural perfection and assessed the effect of dislocation distribution on the frequency dependence of the ferromagnetic resonance (FMR) linewidth in the microwave range. The results demonstrate that, if an external magnetic field is perpendicular to the film surface, electron paramagnetic resonance (EPR) absorption lines correspond to ferromagnetic and spin wave resonances (SWRs). SWR is due to nanostructural surface inhomogeneities. The EPR spectrum of a tangently magnetized film represents a single dipole exchange oscillation spectrum. Parameters of dipole and exchange modes have been determined.

Ground-based optical transmission spectrum of the hot Jupiter HAT-P-1b

Context. Time-series spectrophotometric studies of exoplanets during transit using ground-based facilities are a promising approach to characterize their atmospheric compositions. Aims. We aim to investigate the transit spectrum of the hot Jupiter HAT-P-1b. We compare our results to those obtained at similar wavelengths by previous space-based observations. Methods. We observed two transits of HAT-P-1b with the Gemini Multi-Object Spectrograph (GMOS) instrument on the Gemini North telescope using two instrument modes covering the 320–800 and 520–950 nm wavelength ranges. We used time-series spectrophotometry to construct transit light curves in individual wavelength bins and measure the transit depths in each bin. We accounted for systematic effects. We addressed potential photometric variability due to magnetic spots in the planet’s host star with long-term photometric monitoring. Results. We find that the resulting transit spectrum is consistent with previous Hubble Space Telescope (HST) observations. We compare our observations to transit spectroscopy models that marginally favor a clear atmosphere. However, the observations are also consistent with a flat spectrum, indicating high-altitude clouds. We do not detect the Na resonance absorption line (589 nm), and our observations do not have sufficient precision to study the resonance line of K at 770 nm. Conclusions. We show that even a single Gemini/GMOS transit can provide constraining power on the properties of the atmosphere of HAT-P-1b to a level comparable to that of HST transit studies in the optical when the observing conditions and target and reference star combination are suitable. Our 520–950 nm observations reach a precision comparable to that of HST transit spectra in a similar wavelength range of the same hot Jupiter, HAT-P-1b. However, our GMOS transit between 320–800 nm suffers from strong systematic effects and yields larger uncertainties.

Microwave spectroscopy of superfluid He II

Experimentally observed with dielectric disc resonator technique the resonant microwave absorption- amplification in superfluid He II below λ-point has been interpreted theoretically as a phenomenon in electrically active dielectric medium with low-energy excitations which exist near the ground state of the He–He interatomic bond due to fine structure of spin subsystem in condensed helium phase. The experimentally registered microwave resonant absorption line with fres = 180.3 GHz at T = 1.4 K and fres = 150.0 GHz at T = 2.1 K is closely related to the standard value of roton gap Δ/kB = 8.64 K (179.36 GHz). The measured temperature dependence of the resonant absorption demonstrates an excellent agreement with the corresponding neutron diffraction data for Δ(T) known from different literature sources. From the common point of view the obtained resonant absorption provides a typical example of the microwave spectroscopy which occurs widely among molecular systems with rotational and vibrational degrees of f...

Pulse control in a wide frequency range for a quasi-continuous wave diode-pumped cesium atom vapor laser by a pump modulation in the spectral domain.

Diode-pumped alkali-atom laser (DPAL) has attracted intense attention due to its inherently high quantum efficiency, a good beam quality, and a high potential in the power scaling. However, most of DPAL research has been confined to the continuous wave and only a few pulsed operations have been attempted with limited performances. Here, we proposed and experimentally demonstrated a new scheme using a fast mode-hopping in the pump laser diode (LD), which enabled the quasi-continuous-wave (QCW) pulse modulation in a cesium (Cs) DPAL to control both the pulse width and the repetition rate. The pump wavelength was efficiently modulated in a fast cycle within discrete spectral ranges provided by the mode-hopping in the pump LD. The spectral range was successfully adjusted to include the resonant D2 absorption line of Cs atom to result in an effective gain modulation. Using this proposed scheme, we successfully achieved Cs-DPAL QCW modulation, whose pulse width was varied from tens of microseconds to a few milliseconds and the repetition rate was also variable in a wide frequency range from 10 Hz to 7.0 kHz. Detailed pump modulation method and the corresponding laser characteristics are discussed. The proposed method can be readily applied to pulse modulation of other types of alkali vapor lasers overcoming the previous limitations of DPAL to further expand applications in various light-matter interactions.

An ultra-fast inflow in the luminous Seyfert PG1211+143

Blueshifted absorption lines in the X-ray spectra of AGN show that ultra-fast outflows with typical velocities $v \sim 0.1c$ are a common feature of these luminous objects. Such powerful AGN winds offer an explanation of the observed M-$\sigma$ relation linking the mass of the supermassive black hole and the velocity dispersion in the galaxy's stellar bulge. An extended XMM-Newton study of the luminous Seyfert galaxy PG1211+143 recently revealed a variable multi-velocity wind. Here we report the detection of a short-lived, ultra-fast inflow during the same observation. Previous reports of inflows used single absorption lines with uncertain identifications, but this new result identifies an array of resonance absorption lines of highly ionised Fe, Ca, Ar, S and Si, sharing a common redshift when compared with a grid of realistic photoionization spectra. The redshifted absorption arises in a column of highly ionized matter close to the black hole, with a line-of-sight velocity, $v \sim 0.3c$, inconsistent with the standard picture of a plane circular accretion disc. This may represent the first direct evidence for chaotic accretion in AGN, where accretion discs are generally misaligned to the black hole spin. For sufficient inclinations, the Lense-Thirring effect can break the discs into discrete rings, which then precess, collide and shock, causing near free-fall of gas towards the black hole. The observed accretion rate for the reported infall is comparable to the hard X-ray luminosity in PG1211+143, suggesting that direct infall may be a significant contributor to inner disc accretion.

Ferromagnetic resonance in core-shell nanoparticles with multitype exchange anisotropy

A phenomenological model for magnetodynamics of core-shell nanoparticles is presented. The term core-shell implies, prima facie, that the spin structures (phases) of the particle components are different, no matter whether or not they are chemically identical. The model takes in two main assumptions. First, the interphase boundary is a thin (in comparison with the core and shell scales) transition layer with strongly inhomogeneous spin arrangement. Second, the shell is a granular structure consisting of spin-ordered crystallites with a wide spread of internal anisotropy, including a fraction of ones with extremely high coercivity. The framework developed on that basis, despite its simplicity, provides a unified explanation for the major specific properties of magnetic core-shell particles. Namely, (i) the growth of observed anisotropy field with reduction of the particle size, (ii) the presence of fixed unidirectional anisotropy, and (iii) the existence of rotatable anisotropy that emerges in a threshold manner under an external field. For a nanoparticle with the above-described core-shell architecture, a theory of ferromagnetic resonance with allowance for the superparamagnetic effect is worked out, and the ferromagnetic resonance absorption lines of noninteracting ensembles of such particles are presented. It is demonstrated that all the qualitatively different contributions to the core-shell-induced anisotropy could be evaluated from the data on a temperature sweep of the resonance field. Moreover, to do that, it suffices to use just the samples with random orientation of the particle axes. Preliminary assessment shows that a set of measurements for complete evaluation of the exchange-mediated anisotropies is feasible with the aid of a standard $X$-band spectrometer.