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We present a comprehensive computational study describing the excited state dynamics and consequent photostability of amino-cyclohexenone (ACyO), the central template of mycosporine systems, widely recognized for their photoprotection of aquatic species. Photoexcitation to the first excited electronic state (S1, 1nπ*) of ACyO is considered an optically dark transition, while photoexcitation to the second excited electronic state (S21ππ*) is an optically bright 1ππ* transition and largely responsible for UV absorption properties of this molecule. We show that following initial photoexcitation to S2, ACyO relaxes via two competing deactivation mechanisms, each mediated by an S1/S0 conical intersection, which directs the excited state population to the electronic ground state (S0). Our ab initio computational results are supported with nonadiabatic dynamics simulation results, yielding an excited state lifetime of ∼280 fs for this system in vacuo. These results explain the inherent photostability of this core structure, commonplace in a wide range of microorganisms. [ABSTRACT FROM AUTHOR]

A new class of acoustic black hole (ABH) waveguides is presented, which relies in its operation on an array of optimally designed functionally graded perforated rings (FGPRs). In this manner, the developed ABH is provided with built-in energy dissipation characteristics generated by virtue of the flow through perforations, which enhances its acoustic absorption behavior and makes the speed of the propagating waves vanish faster when reaching the end of the waveguide. Furthermore, the particular design of the rings enables sandwiching of additional porous absorbing layers between the rings to further boost the absorption characteristics of the proposed ABH. Accordingly, the operating principle of the new class of ABH is radically different from that of the conventional ABH that employs sequential solid-flat rings of decreasing inner radii to create a virtual power law taper necessary for generating the black hole effect, but through reactive means rather than the effective dissipative means of the proposed ABH. Therefore, this paper develops a transfer matrix modeling (TMM) approach to model the absorption and reflection characteristics of the new class of ABH, in an attempt to predict its behavior, optimize the selection of its design parameters, and more importantly, demonstrate its merits as effective means for controlling sound propagation. Numerical examples are presented to highlight the merits and behavior of the proposed ABH. Predictions of the TMM are validated against experimental results that are available in the literature for one and two micro-perforated plates. Comparisons are also established between the ABH with FGPR and the conventional ABH in order to distinguish the behavior and underlying principles of their operations. [ABSTRACT FROM AUTHOR]

The dispersion properties of the absorption coefficients [α(ν)] of different multi-component silicate oxide glasses have been studied in the frequency region below the boson peak by using THz-time-domain spectroscopy. The value of α(ν)/ν2 has been shown to exhibit a minimum level (R) at low frequency and subsequently a linear increase in the form of r(ν/νBP + E) with increasing frequency, where νBP is the boson peak frequency and R, r, and E are material-specific constants. It has also been found that R ∝ r and E is a constant common to most glasses. This α(ν)/ν2 behavior is ascribed to the dispersion property of the light-vibration coupling coefficient under the reasonable vibrational density of state function. The minimum (constant) and linear terms of the α(ν)/ν2 spectrum are originated from the physical/chemical disorder-induced charge fluctuations in the long-range scale (constant term) and short-range scale (linear term), respectively. The fluctuating charge (σ1) caused by uncorrelated, long-range disorders has primary significance for determining the sub-THz absorption dispersion properties, and its value has been determined for each glass material. [ABSTRACT FROM AUTHOR]

A route to assess non-linear light–matter interactions from the increasingly popular GW-Bethe–Salpeter equation (GW-BSE) method is outlined. In the present work, the necessary analytic expressions within the static-screened exchange approximation of the BSE are derived. This enables a straightforward implementation of the computation of the first hyperpolarizability as well as two-photon absorption processes for molecular systems. Benchmark calculations on small molecular systems reveal that the GW-BSE method is intriguingly accurate for predicting both first hyperpolarizabilities and two-photon absorption strengths. Using state-of-the-art Kohn–Sham references as a starting point, the accuracy of the GW-BSE method rivals that of the coupled-cluster singles-and-doubles method, outperforming both second-order coupled-cluster and time-dependent density-functional theory. [ABSTRACT FROM AUTHOR]

Realization of microwave-absorbing materials with "small thickness, light weight, broad bandwidth, and low reflectivity" is an invariable topic. In this paper, Sm2Fe14BHx/polyurethane (SFBH/PU) composites with planar anisotropy were prepared by reduction–diffusion (R/D) and water bath hydrogenation (WBH) process. A minimum reflection loss (RL) value reaches −59.7 dB at the perfect matching frequency of 13.79 GHz with a thickness of only 1.035 mm. Compared with unhydrogenated SFB, the bandwidth and reflectivity are significantly improved. It is mainly attributed to the fact that introduction of hydrogen atoms effectively modulates the electromagnetic parameters and increases the Snoek limit ((μ i − 1) f r) , which leads to the improvement of the high-frequency microwave absorption performance. In addition, the bandwidth equation is derived and simplified from the perspective of the reflected wave at the interface, which is in good agreement with the measured results. [ABSTRACT FROM AUTHOR]

The first-order molecular hyperpolarizability (β) dispersion was measured in seven chalcone-based molecules utilizing the tunable femtosecond hyper-Rayleigh scattering (tHRS) technique. Additionally, a theoretical model based on photophysical parameters was employed to better understand β dispersion. Due to the distinct substitution patterns of the aryl/heteroaryl rings within the chalcone structure, varying profiles of one- and two-photon absorption spectra and β dispersion were observed. The applied model highlighted two important factors contributing to achieving high β values: (i) the presence of red-shifted one-photon and two-photon absorption bands; and (ii) the number of discernible absorption bands. To contextualize these results with other molecular structures, we employed the HRS figure of merit (FOM). Remarkably, it was revealed that chemically engineered small chalcone molecules exhibit a FOM comparable to larger quadrupolar and octupolar ones. This underscores the significance of tHRS scattering measurements and their correlation with absorptive parameters in the design and characterization of nonlinear optical materials. [ABSTRACT FROM AUTHOR]

Period phase gradient metasurface plays a great role in promoting the innovation of acoustic application devices. However, harnessing the internal thermal viscosity of the period phase gradient metasurface to realize sound absorption and non-reciprocal transmission faces the narrow working frequency band and uncontrollable efficiency. In this paper, we propose a lossy metasurface by embedded microperforated walls to realize sound redirection and absorption with high efficiency than 90% simultaneously. The phase modulation is realized using an opening channel, which can cover the 2 π phase range in a broadband frequency range by changing the channel depth. The loss introduced by the microperforated walls can achieve efficient sound energy dissipation when negative reflection occurs. The functions can be switched between wave redirection and wave absorption by rotating the metasurface. In addition, this metasurface can redirect the incident wave below −10° and absorb the incident wave above 25° over a wide frequency range from 1500 to 6500 Hz. The simulation and experiment results of our design are in excellent agreement. This research provided a new bridge to integrate wave redirection and absorption with microperforated walls and may have potential applications in acoustic sensing, sound source identification, and mechanical fault diagnosis. [ABSTRACT FROM AUTHOR]

The research and development of absorbing materials with high absorbing capacity, wide effective absorption bandwidth, and lightweight has always been interesting. In this research, a facile hydrothermal method was used to prepare MnFe2O4, and the grain size of MnFe2O4 decreased with increasing hydrothermal temperature. When the size of MnFe2O4 nanoparticles is less than 10 nm, its quantum size effect and surface effect make its electromagnetic microwave absorption performance greatly optimized. When the thickness of MnFe2O4-110 °C is 2.57 mm, the minimum reflection loss (RLmin) is −35.28 dB. Based on this, light porous diatomite and a three-dimensional polyaniline network are introduced. Diatomite is used as the base material to effectively reduce the agglomeration of MnFe2O4 quantum dots. The relatively high surface area introduced by a three-dimensional network of polyaniline promotes the orientation, interfacial polarization, multiple relaxation, and impedance matching, thereby generating further dielectric loss. Additionally, the magnetic properties of manganese ferrite and the strong electrical conductivity of polyaniline play an appropriate complementary role in electromagnetic wave absorption. The RLmin of MnFe2O4/PANI/diatomite is −56.70 dB at 11.12 GHz with an absorber layer thickness of 2.57 mm. The effective frequency bandwidth (RL < −10 dB) ranges from 9.21 to 18.00 GHz. The absorption mechanism indicates that the high absorption intensity is the result of the synergistic effect of impedance matching, conduction losses, polarization losses, and magnetic losses. [ABSTRACT FROM AUTHOR]

We have effectively shown a technique for significantly altering the nonlinear saturable absorption (SA) properties of nanocomposite films (NCFs) based on poly(3,4-ethylenedioxythiophene) doped with poly(4-styrenesulfonate) (PEDOT:PSS) and molybdenum disulfide (MoS2) by regulating MoS2 concentration and input pulse energy of the laser. The NCFs are made using the straightforward drop-cast process on a glass substrate with varying quantities of MoS2. The produced NCFs' refractive index (n) and extinction coefficient (k) values are determined using the Kramers–Kronig equations. Nonlinear studies show that the optical nonlinearity of pure PEDOT:PSS changes when mixed with MoS2. The Pauli blocking has been observed in MoS2/PEDOT:PSS NCFs. This leads to enhanced SA in NCF. The open-aperture Z-scan approach is used for the nonlinear optical research, and a nanosecond pulsed laser with a wavelength of 532 nm is used for the excitation. The findings obtained show the NCFs' strong SA qualities. [ABSTRACT FROM AUTHOR]

The rare earth alloy Y 2 Co 17 − x Ni x was prepared by a low-cost co-precipitation reduction-diffusion process, and its crystal structure, static magnetic properties, and microscopic morphology were systematically characterized. The effects of Ni doping with different contents on the electromagnetic parameters and wave absorption properties of Y 2 Co 17 − x Ni x /polyurethane(PU) compounds were researched in the frequency range of 0.1–18 GHz. The results show that the static magnetic properties and wave absorption properties change significantly with Ni doping, and the maximum reflection loss of Y 2 Co 14 Ni 3 /PU reaches − 89.7 dB at 2.9 mm thickness, and the maximum reflection loss peaks of Y 2 Co 17 /PU and Y 2 Co 16 Ni 1 /PU are at 1.316 and 1.515 GHz, which is at the center frequency of the L-band. With Ni doping, the effective absorption bandwidth of the compounds at a frequency above 3 GHz is greatly increased. The physical factor in the bandwidth calculation was modified, and the effective absorption bandwidth of the material was calculated theoretically, and the error was less than 5 % compared with the experimental value. [ABSTRACT FROM AUTHOR]

In the present study, we have explored the absorption properties of a monolayer graphene-based photonic heterostructure, which consists of topological photonic configurations, graphene, and a Bragg mirror. The optical attributes were computed by using the 4 × 4 transfer matrix method. The results indicate that the creation of topological interface states and strong coupling between these resonant modes result in mode splitting, leading to the formation of hybrid modes known as coupled topological interface states with unity transmittance. The number of absorption modes can be modulated with an appropriate selection of cascaded photonic structures. Our proposed design with 1, 3, 5, and 7 cascaded topological photonic structures provides 1, 5, 9, and 13 absorption modes with greater than 90 % absorption. The findings also reveal that absorption peak strength is greatly influenced by Fermi-level and magnetic fields; switching of the modes from absorption to reflection and vice versa is achieved by suitable electrical and magnetic biasing. Our proposed design offers various applications, such as switchable filters, absorbers, and modulators. [ABSTRACT FROM AUTHOR]

Absorption of electromagnetic (EM) wave has been widely studied and applied in EM, optics, and material research. By constructing an adaptive multi-mode absorption, an EM absorber approach that can be used in a variety of EM environments is provided in this research. This property demonstrates the absorber has an improved environment compatibility. It is used as an application example to address the issue that has recently come up in phased array research on the need to reduce the coupling between antenna elements in varied beam-scanning cases. After analyzing the electric and magnetic characteristics of a patch antenna array in different beam-scanning states, an absorber structure is constructed, with electric absorption in the sum beam case, magnetic absorption in the difference beam case, and combined electric-magnetic absorption in other beam scanning cases. The proposed method is systematically investigated and, finally validated by simulation and measurement evidently. In arbitrary beam-scanning states, the absorber exhibits good absorption and coupling reduction performance, while the radiation performance of the array is well maintained after introducing the absorber. This research can be used in absorber and coupling reduction studies, as well as, potentially in metamaterial and electromagnetic compatibility (EMC). [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive study of the theory of entangled two-photon emission/absorption (E2P-EA) between a many-level cascade donor and a many-level acceptor (which could be quantum dots or molecules) using second-order perturbation theory and where the donor–acceptor pair is in a homogeneous but dispersive medium. To understand the mechanism of E2P-EA, we analyze how dipole orientation, radiative lifetime, energy detuning between intermediate states, separation distance, and entanglement time impact the E2P-EA rate. Our study shows that there are quantum interference effects in the E2P-EA rate expression that lead to oscillations in the rate as a function of entanglement time. Furthermore, we find that the E2P-EA rate for a representative system consisting of two quantum dots can be comparable to one-photon emission/absorption (OP-EA) when donor and acceptor are within a few nm. However, the E2P-EA rate falls off much more quickly with separation distance than does OP-EA. [ABSTRACT FROM AUTHOR]

This article describes the temporal evolution of rotationally and vibrationally non-Boltzmann CN X2Σ+ formed behind reflected shock waves in N2–CH4 mixtures at conditions relevant to atmospheric entry into Titan. A novel ultrafast (i.e., femtosecond) laser absorption spectroscopy diagnostic was developed to provide broadband (≈400 cm−1) spectrally resolved (0.02 nm resolution) measurements of CN absorbance spectra belonging to its B2Σ+ ← X2Σ+ electronic system and its first four Δv = 0 vibrational bands (v″ = 0, 1, 2, 3). Measurements were acquired behind reflected shock waves in a mixture with 5.65% CH4 and 94.35% N2 at initial chemically and vibrationally frozen temperatures and pressures of 4400–5900 K and 0.55–0.75 bar, respectively. A six-temperature line-by-line absorption spectroscopy model for CN was developed to determine the rotational temperature of CN in v″ = 0, 1, 2, and 3, as well as two vibrational temperatures via least-squares fitting. The measured CN spectra revealed rotationally and vibrationally non-Boltzmann population distributions that strengthened with increasing shock speed and persisted for over 100 µs. The measured vibrational temperatures of CN initially increase in time with the increasing CN mole fraction and eventually exceed the expected post-shock rotational temperature of N2. The results suggest that strong chemical pumping is ultimately responsible for these trends and that, at the conditions studied, CN is primarily formed in high vibrational states within the A2Π or B2Σ+ state at characteristic rates, which are comparable to or exceed those of key vibrational equilibration processes. [ABSTRACT FROM AUTHOR]

In Part I of this work published previously, it was proved from the transmission-line theory that impedance matching (IM) theory should be replaced by wave cancellation theory, film is different from the material, and the phase effects from interfaces should be considered in quarter wavelength theory. In this Part, it is shown that energy penetration for a film cannot be defined and IM is flawed because it cannot be proved theoretically or shown to be consistent with experimental data. The multi-absorption peaks in a film originate from wave cancellation under the constraint of energy conservation rather than from the resonances from the material. [ABSTRACT FROM AUTHOR]

The mechanism for microwave absorption in a film has previously been numerically verified from the theoretical formula for RL and attributed to angular and amplitude effects with a simple geometrical representation from energy conservation unique to the film. Starting from the case where |RL| = 0, using basic transmission-line theory and mathematics, it is confirmed theoretically here that the mechanism for absorption mechanism in a film, responsible for the minima of the reflection loss RL/dB, is best explained by wave cancelation theory rather than by impedance matching theory. This theoretical proof also reveals that the mechanisms for a film and material are different. The flaws of neglecting the phase effects of interfaces in a film in quarter-wavelength theory are also quantitatively discussed from transmission-line theory. Contrary to the theory held currently, the reported minima of RL/dB originate from phase effects in the film rather than from the resonance peaks for the intrinsic frequencies of a material. [ABSTRACT FROM AUTHOR]

The comparison of experimentally found absorption limits, and their variations in compound semiconductors, with theoretical expectations was never a particularly studied subject, although absorption limits in semiconductors could be critical to certain optoelectronic device applications. We introduce a model, which accurately fits the distinct absorption saturation parameter linked to the effective electron density of states. [ABSTRACT FROM AUTHOR]

A new time-resolved opacity spectrometer (OpSpecTR) is currently under development for the National Ignition Facility (NIF) opacity campaign. The spectrometer utilizes Icarus version 2 (IV2) hybridized complementary metal–oxide–semiconductor sensors to collect gated data at the time of the opacity transmission signal, unlocking the ability to collect higher-temperature measurements on NIF. Experimental conditions to achieve higher temperatures are feasible; however, backgrounds will dominate the data collected by the current time-integrating opacity spectrometer. The shortest available OpSpecTR integration time of ∼2 ns is predicted to reduce self-emission and other late-time backgrounds by up to 80%. Initially, three Icarus sensors will be used to collect data in the self-emission, backlighter, and absorption regions of the transmission spectrum, with plans to upgrade to five Daedalus sensors in future implementations with integration times of ∼1.3 ns. We present the details of the diagnostic design along with recent characterization results of the IV2 sensors. [ABSTRACT FROM AUTHOR]

The shedding-scheme transition of hemispherical wake is investigated with time-resolved tomographic particle image velocimetry. Experiments are carried out with Reynolds numbers based on the hemisphere radius R in the range of R e r = 924 – 2315 , crossing the critical value of R e r ≈ 2000. The variation of the hemispherical wake across the critical Reynolds number is carefully studied, and a detailed mechanism of the shedding-scheme transition is explored. A singular-shedding pattern of hairpin vortices at a low Rer is replaced by a pairing-shedding pattern at a moderate Rer, and finally, a less ordered wake and an unstable shedding pattern are observed at Rer > 2000. The onset of the pairing-shedding pattern is due to a streamwise modulation caused by the varicose modes, which is related to the Kelvin–Helmholtz (K–H) instability. Consequently, the pseudo-periodicity induced by the K–H instability is observed in the wake. When Rer > 2000, the stronger sinuous modulation intensifies interactions among the hairpin vortices, leading to frequent absorption and annihilation of those coherent structures, which further makes the dominant frequency of main hairpin vortices halved downstream. [ABSTRACT FROM AUTHOR]

In this article, an immiscible three-phase/three-component lattice Boltzmann flux solver (TPLBFS) based on diffusion interface method is proposed, which can achieve three-phase flow simulation with high density ratio (1:1000). This model quickly solved (1) the flux at the grid interface using the lattice Boltzmann method (LBM) solution format and (2) the Navier–Stokes (NS) equation and Cahn–Hilliard (CH) equation using a unified format. Compared to LBM, TPLBFS can be applied to unstructured networks. Moreover, TPLBFS can independently add or remove source items and has high secondary development features. Its outstanding computing power has been demonstrated by multiple two-dimensional/three-dimensional (2D/3D) examples, including 2D liquid lens as well as 3D bubble absorption and bubble rising in a three-phase system. [ABSTRACT FROM AUTHOR]

π modes are unique topological edge states appearing in Floquet systems with periodic modulations of the underlying lattice structure in the evolution variable, such as dynamically modulated Su–Schrieffer–Heeger (SSH) lattices. These edge states are anomalous states usually appearing between Floquet replicas of the same band, even if the standard topological index remains zero for this band. While linear and nonlinear π modes were observed in conservative systems, they have never been studied in the nonlinear regime in the non-Hermitian systems with structured gain and losses. Here, we show that the SSH waveguide array with periodically oscillating waveguide positions in the propagation direction and with the parity-time symmetric refractive index landscape can support π modes that are damped or amplified at different ends of the array. By including nonlinearity and nonlinear absorption into our continuous system, we achieve stable lasing in the π mode at one end of the array. The representative feature of this system is that lasing in it is thresholdless and occurs even at low gain–loss amplitudes. The degree of localization of lasing π modes can be flexibly controlled by the amplitude of transverse waveguide oscillations. This work therefore introduces a new type of topological Floquet laser and a route to manipulate π modes by structured gain and losses. [ABSTRACT FROM AUTHOR]

Cadmium oxide (CdO) has recently attracted attention as a material with controllable properties tailored for optoelectronic and nanophotonic devices due to its superior mobility. However, its potential application in near-infrared (NIR) remains to be explored. In this work, we demonstrate that the epsilon-near-zero (ENZ) wavelength and nonlinear optical properties of CdO films can be effectively tuned by Mo doping. The results show that Mo doping increases the electron concentration as well as improve the crystalline quality of CdO. With increasing Mo doping, we achieve blueshifts of the ENZ wavelength from 2.89 to 1.56 μm. The nonlinear absorption (NLA) behavior at 1550 nm changes from reverse saturable absorption to saturable absorption with increasing Mo content. Moreover, significant improvement in NLA performance with nonlinear absorption coefficient β = −72 cm/GW is observed at the highest doping content. Our work shows that doped CdO films with tunable optoelectrical and nonlinear optical properties can be an ideal candidate for optoelectronic and nanophotonic application in the NIR region. [ABSTRACT FROM AUTHOR]

In this paper, a dual-band and dual-broadband terahertz (THz) metamaterial absorber (MA) using two asymmetric rectangular rings is proposed and studied. The proposed bifunctional MA possesses not only the dual-band absorption performance with absorptivities of 97.81% and 99.53% at 2.07 and 2.88 THz but also the dual-broadband absorption performance with absorptivity above 90% in two frequency ranges of 5.74–6.98 and 9.81–10.83 THz. The distributions of electric fields at resonant frequencies are utilized to analyze the working principle of the proposed bifunctional MA. Moreover, the influences of incident angle and polarization angle on dual-band and dual-broadband absorption performance are also investigated. Different from the previous MAs with asymmetric resonators, our bifunctional MA has polarization insensitivity despite the use of two asymmetric rectangular rings. Therefore, our design idea can be effectively utilized in the development of bifunctional MAs with simple structures and polarization insensitivity. [ABSTRACT FROM AUTHOR]

We present measurements of the 2p-3d transition opacity of a hot molybdenum–scandium sample with nearly half-vacant molybdenum M-shell configurations. A plastic-tamped molybdenum–scandium foil sample is radiatively heated to high temperature in a compact D-shaped gold Hohlraum driven by ∼30 kJ laser energy at the SG-100 kJ laser facility. X rays transmitted through the molybdenum and scandium plasmas are diffracted by crystals and finally recorded by image plates. The electron temperatures in the sample in particular spatial and temporal zones are determined by the K-shell absorption of the scandium plasma. A combination of the IRAD3D view factor code and the MULTI hydrodynamic code is used to simulate the spatial distribution and temporal behavior of the sample temperature and density. The inferred temperature in the molybdenum plasma reaches a average of 138 ± 11 eV. A detailed configuration-accounting calculation of the n = 2–3 transition absorption of the molybdenum plasma is compared with experimental measurements and quite good agreement is found. The present measurements provide an opportunity to test opacity models for complicated M-shell configurations. [ABSTRACT FROM AUTHOR]

The application of microwave absorption materials, which can effectively convert electromagnetic energy into thermal energy and/or other forms of energy, can effectively solve the increasingly serious electromagnetic pollution. As a type of promising microwave absorption material, ternary transition metal carbides/nitrides MAX phases possess layered structure and superior conduction loss capability. However, poor impedance matching and single polarization loss type seriously hinder their improvement of microwave absorption performance. High-entropy engineering is expected to be an effective strategy to address the above problems simultaneously. Herein, a series of low-, medium-, and high-entropy MAX phases with Ti2AlC structure were successfully synthesized and their structure, composition, and morphology were comprehensively characterized. High-entropy MAX phase (Ti1/5Zr1/5V1/5Nb1/5Ta1/5)2AlC presents excellent microwave absorption performance with the optimal minimum reflection loss (RLmin) of −47 dB at 11.92 GHz (a thickness of 2.4 mm) and optimal effective absorption bandwidth of 3.92 GHz between 8.48 and 12.4 GHz (a thickness of 2.78 mm), which are better than those of our prepared low-/medium-entropy MAX phases as well as most of the other previously reported MAX phases. Such excellent microwave absorption performance of (Ti1/5Zr1/5V1/5Nb1/5Ta1/5)2AlC is attributed to high-entropy engineering, which not only optimizes the impedance matching through regulating permittivity but also introduces more polarization loss type and amount. This work reveals that high-entropy engineering is not only a workable method to enhance the microwave absorption performance in MAX phases, but also an effective strategy to tailor the balance between impedance matching and loss capability through compositional design in single-phase systems. [ABSTRACT FROM AUTHOR]

Various mechanisms of absorption including both electric-dipole excitations and magnetic ones in a broadband (5–5000 cm−1) polarized transmission and reflection spectra were studied in orthoferrite TbFeO3 using a coherent submillimeter, pulsed THz, and IR Fourier transform spectroscopy. The classical oscillator model and generalized four-parameter model were used to analyze the spectra obtained, and the parameters of the models were determined. We analyzed main absorption processes, which include contributions of both phonons and multi-phonon processes as well as electron transitions in Tb3+ ions and two antiferromagnetic resonance modes in the Fe subsystem. As a result, the spectra of real and imaginary parts of permeability and permittivity were obtained. A distinctive feature of the studied electrodynamic response in TbFeO3 is a significant absorption in the THz range due to multi-phonon processes, which exceeds optical phonon contribution by an order of magnitude at room temperature. [ABSTRACT FROM AUTHOR]

A structure composed of a hexagonal array of Si nanodisks having toroidal dipole resonances and a reflecting mirror separated by a SiO2 spacer is proposed as a platform that exhibits narrow-band perfect absorption in the Si sub-bandgap wavelength range for a CMOS compatible Si based photodetector operating below the bandgap range. The numerical simulation reveals that the structure possesses Fabry–Pérot bound states in the continuum at proper spacer thicknesses due to the interference between the toroidal dipole and its image dipole. By slightly detuning the spacer thickness to meet the critical coupling condition, narrow-band perfect absorption appears despite assumption of a very small extinction coefficient (5 × 10−4). The wavelength of the perfect absorption is controlled in a wide range by the structural parameters of a Si nanodisk hexagonal array and is insensitive to the fluctuation of the extinction coefficient and the choice of a metallic mirror. In the structure, over 90% of incident power can be absorbed in the Si region. This suggests that the structure can be used as a narrow-band photodetector operating in the Si sub-bandgap wavelength range. We also evaluate the sensing performance of the proposed structure as an intensity based refractive index sensor operating in the near-infrared range. [ABSTRACT FROM AUTHOR]

Photophysical, photovoltaic, and charge transport properties of fused core-modified expanded porphyrins containing two pyrroles, one dithienothiophene (DTT) unit, and 1–4 thiophenes (1–4) were inspected by using density functional theory (DFT) and time-dependent DFT. Compounds 1–3 have been investigated experimentally before, but 4 is a theoretical proposal whose photophysical features match those extrapolated from 1 to 3. They exhibit absorption in the range of 700–970 nm for their Q bands and 500–645 nm for their Soret bands. The rise of thiophene rings placed in front of the DTT unit in the expanded porphyrin ring causes a bathochromic shift of the longest absorption wavelength, leading to near-infrared absorptions, which represent 49% of the solar energy. All the systems show a thermodynamically favorable process for the electron injection from the dye to TiO2 and adsorption on a finite TiO2 model. The electron regeneration of the dye is only thermodynamically feasible for the smallest expanded porphyrins 1 and 2 when I−/I3− electrolyte is used. The charge transport study shows that for voltages lower than 0.4 V, junctions featuring pentaphyrin 1 and octaphyrin 4 are more conductive than those containing hexaphyrin 2 or heptaphyrin 3. The results showed that the four fused core-modified expanded porphyrins investigated are potential dyes for applications in dye-sensitized solar cells, mainly pentaphyrin 1 and hexaphyrin 2. Moreover, increasing the number of thiophene rings in the macrocycle proved fruitful in favoring absorption in the near-infrared region, which is highly desired for dye-sensitized solar cells. [ABSTRACT FROM AUTHOR]

We present a hollow-core fiber (HCF) based transient absorption experiment, with capabilities beyond common titanium:sapphire based setups. By spectral filtering of the HCF spectrum, we provide pump pulses centered at 425 nm with several hundred nJ of pulse energy at the sample position. By employing the red edge of the HCF output for seeding CaF2, we obtain smooth probing spectra in the range between 320 and 900 nm. We demonstrate the capabilities of our experiment by following the ultrafast relaxation dynamics of a radical cationic photocatalyst to prove its pre-association with an arene substrate, a phenomenon that was not detectable previously by steady-state spectroscopic techniques. The detected preassembly rationalizes the successful participation of radical ionic photocatalysts in single electron transfer reactions, a notion that has been subject to controversy in recent years. [ABSTRACT FROM AUTHOR]

This work presents the investigations of the impact of an increasing electron correlation in the hierarchy of coupled-cluster methods, i.e., CC2, CCSD, and CC3, on two-photon absorption (2PA) strengths for the lowest excited state of the minimal rhodopsin's chromophore model—cis-penta-2,4-dieniminium cation (PSB3). For a larger chromophore's model [4-cis-hepta-2,4,6-trieniminium cation (PSB4)], CC2 and CCSD calculations of 2PA strengths were performed. Additionally, 2PA strengths predicted by some popular density functional theory (DFT) functionals differing in HF exchange contribution were assessed against the reference CC3/CCSD data. For PSB3, the accuracy of 2PA strengths increases in the following order: CC2 < CCSD < CC3, with the CC2 deviation from both higher-level methods exceeding 10% at 6-31+G* basis sets and 2% at aug-cc-pVDZ basis set. However, for PSB4, this trend is reversed and CC2-based 2PA strength is larger than the corresponding CCSD value. Among the DFT functionals investigated, CAM-B3LYP and BHandHLYP provide 2PA strengths in best compliance with reference data, however, with the error approaching an order of magnitude. [ABSTRACT FROM AUTHOR]

Extreme ultraviolet polarizers are crucial for in-depth investigations of light–matter interaction and cutting-edge applications in modern optics. Here, we propose a strategy for extreme ultraviolet wire grid polarizers with superior performance based on vacuum guiding. Owing to the suitable material absorption and vacuum guiding effect, the designed polarizers exhibit an inverse polarization effect and achieve polarization extinction ratios exceeding 100 at various extreme ultraviolet bright lines. Furthermore, the optimized a-silicon-based and molybdenum-based wire grid polarizers achieve the average transmissivity of the target polarization over 30% and 40% at 90–110 and 50–65 nm, respectively, while maintaining a polarization extinction ratio greater than 100. Comparisons with conventional devices further validate the exceptional performance of our device. [ABSTRACT FROM AUTHOR]

This paper presents a numerical analysis, using the rigorous-coupled-wave-analysis method, of microwave and far-IR radiation scattering on thin conductive films of nanometer thickness under the condition of total internal reflection. Transmittance, reflection, and absorption studies have shown the possibility of overcoming the 50% absorption limit with frequency-independent behavior; the absorption above the critical angle reaches values greater than 90%. In addition, the influence of such thin metal-dielectric structure on the Goos–Hänchen shift is considered. At maximum absorption, calculations showed its absence in both TE and TM polarizations. The numerical analysis was carried out for a plane wave and for a 500 cm diameter beam. [ABSTRACT FROM AUTHOR]

It is known that total absorption of flexural waves in a thin beam is possible through the use of monopole-dipole scatterers. In this study, we introduce a pair of identical monopole scatterers for near-total absorption of flexural waves in a thin and wide beam. Despite the two scatterers being both of the monopole type, the resonant modes of the scatterer pair exhibit monopole and dipole properties. By selecting the proper width for the beam, the two resonant modes degenerate, which leads to the total absorption. Although the beam is considerably wide, the frequency range of interest remains below the cut-on frequency of the n = 1 propagating mode, ensuring one-dimensional flexural wave propagation. Further simulations and theoretical analysis revealed that the degeneracy of the monopole and dipole modes results from their interaction with a higher-order localized flexural mode. The simulation results demonstrate absorption exceeding 99%, complemented by experimental data showing approximately 90% absorption. [ABSTRACT FROM AUTHOR]

Lanthanide-doped nanoparticles (LnNPs) show unique optical properties and have been demonstrated in various applications, including imaging, optogenetics, photothermal therapy, photodynamic therapy, light-controlled release/cross-linking, anticounterfeiting, lasing, sensing, and super-resolution microscopy. One of the key and urgent limitations of LnNPs is the weak and narrow absorption of lanthanides. Fabrication of heterostructures will overcome this hurdle and enhance the performance of LnNPs. Developing novel heterostructures to enhance the absorption of lanthanides and studying the energy transfer pathways and efficiencies are of broad interest to the chemical and physical research community. There is currently no systematic review to summarize different types of LnNP heterostructures. Thus, this review will summarize five types of heterostructures combining LnNPs with organic and inorganic dyes, plasmonics, semiconducting quantum dots, and metal–organic frameworks. The enhancement of absorption and the improvement of light conversion performance are compared and discussed. This review also discusses the energy transfer pathways and efficiencies between LnNPs and other components and provides suggestions to form heterostructures with enhanced absorption and efficient energy transfer for future applications. We hope this review will further inspire active development and study of lanthanide-based heterostructures with stronger absorption, better light conversion performance, and ease of multifunctionality. [ABSTRACT FROM AUTHOR]

It was recently shown that the use of Coulomb logarithms appropriate for bremsstrahlung radiation (rather than transport processes) along with corrections for the Langdon effect and ion screening reproduced measurements of collisional absorption in well-characterized underdense plasmas [D. Turnbull et al., Phys. Rev. Lett. 130, 145103 (2023)]. However, it was recognized at the time that the use of the standard absorption-reduction factor from Langdon's seminal paper was inconsistent with the use of Coulomb logarithms that are thermally averaged over a Maxwellian electron-velocity distribution function. A more accurate approach would be to average over the expected super-Gaussian distribution function while accounting for the Gaunt factor's velocity dependence, which somewhat mitigates the Langdon effect; however, at that time, this theory matched the data less well. This conflict is now eliminated with the additional insight that the ionization state of our mid-Z ion species (when present) was lower than had been assumed, as evidenced by the Thomson-scattering data and time-dependent Cretin simulations. We are now able to show that an improved treatment of the Langdon effect provides the best match to data. Otherwise, the prior conclusions remain unchanged. We also show an example of the substantial expected impact to the absorption rate in calculations of indirect-drive hohlraums. [ABSTRACT FROM AUTHOR]

The fraction of light absorbed in a material is a key parameter for a wide range of optoelectronic and energy devices, including solar cells, light emitting diodes, and photo(electro)chemical devices. It can reveal detailed performance information and establish a material's theoretical efficiency limits. However, measuring absorption accurately is challenging, especially due to scattering effects at the macroscale and achieving perpendicular illumination over a small area at the microscale. In this tutorial, we present concepts and best practices in measuring absorption at both the macro- and micro-scale. We also give examples of using absorption to reveal critical optoelectronic information in energy devices. This work aims at standardizing the recording of absorption measurements across a number of fields, allowing for improved microscale understanding of a wide range of samples. [ABSTRACT FROM AUTHOR]

As a rediscovered ternary two-dimensional (2D) material, defect-rich Znln2S4 has great potential for energy-harvesting applications. However, the effect of defects on its physical properties and device performance remains elusive. Herein, we explored the influence of defects (S vacancies and In–Zn substitutions) in few-layer Znln2S4 on the charge transport and photoelectric performance. It is demonstrated that the defect-rich Znln2S4 device exhibits two-dimensional variable range hopping transport mechanism, with uniform charge transport along the channel and low contact resistance at the electrical contacts of Znln2S4/Au. Importantly, due to the contribution of the donor and acceptor energy levels inside the bandgap, the flake exhibits pronounced extrinsic absorption, leading to the competitive photodetector performance under sub-bandgap photo-excitation. Explicitly, the device exhibits a maximum responsivity of 4.08 × 104 A W−1, a photo-gain of >108 electrons per photon, and a specific detectivity of ∼1015 Jones under 532 nm laser excitation, with detection wavelength extending from 400 to 980 nm. Our findings underscore the significant potential of defect-engineering to enrich the functionalities of 2D semiconductors. [ABSTRACT FROM AUTHOR]

We report the wavelength dependencies of the two-photon absorption coefficients β as well as the nonlinear refractive index n2 of undoped β-Ga2O3 single crystal in the spectral range 350–515 nm (0.51 < Ephoto/Eg < 0.75). Femtosecond Z-scan measurements show that n2 decreases monotonically toward the shortwave side, while the maximum value of n2 is 5.0 × 10−19 m2/W near half of the bandgap, Eg. Interestingly, a second upward trend in β was observed when the incident photon energy is larger than 0.6Eg, indicating the impact of additional inter-band transitions with higher energy. A higher-energy band-to-band transition around 6.0 eV was determined by both femtosecond nondegenerate two-photon absorption spectroscopy and ab initio calculations. Our results could provide guidance for designing nonlinear β-Ga2O3 photonic devices in the UV-visible spectral range. [ABSTRACT FROM AUTHOR]

The stacked thin films have recently been of great interest for enhancing the optical and thermal absorption of the system via their specific optical properties depending on the optical wavelength and layer thickness. Here, by using Maxwell's equation for the electromagnetic fields penetrating thin films, we simulated in detail the absorption of the nanometer-thick thin film of several materials, such as Au, Ag, Cu, and Al, and figured out the optimal thickness range for the outer layers exposed to incoming field to optimize the energy harvesting. In particular, the absorption of the film supported by a totally reflective layer at the back of the structure could be significantly enhanced, and the maximal absorption happens at a layer much thinner than that in the case of the film solely irradiated by the field. These results could help suitably choosing of detailed thickness for the structure to optimize the field effect on a specific layer. [ABSTRACT FROM AUTHOR]

Coupling-induced transparency (CIT) and absorption (CIA) of transmission signals were experimentally observed in a single planar hybrid structure specially designed to consist of a yttrium iron garnet film and three concentric inverted-split-ring resonators (ISRRs). The observation of both CIT and CIA was ascribed to the cooperative effect of the interaction of magnons with three decoupled ISRRs' photon modes and the traveling waves along the microstripline. An analytical model developed based on the balance between the coherent and dissipative multiple-paths interactions precisely reproduced both CIT and CIA experimentally observed from a single hybrid system. This work, promisingly, can provide guidance for the design of efficient, flexible, and well-controllable magnon–photon hybrid devices that are highly in demand for applications to quantum technologies currently under development. [ABSTRACT FROM AUTHOR]

With the advancement and up-gradation of wireless technology, people worldwide are surrounded by microwaves, however, with the brighter side comes the darker side too. These microwave/electromagnetic wireless signals interfere with the environment/mankind and are referred to as electromagnetic interference (EMI)/electromagnetic or microwave pollution. Microwave/electromagnetic absorbers are used to mitigate this EMI or electromagnetic pollution. Researchers have been working on microwave absorbents of different kinds to save humans, their gadgets, electronically printed cards, etc. to create a healthy and radiation-free environment. Recently, there is an advancement in different forms of ferrite absorbers. This review presents a description of what are ferrite-based microwave absorbers, the preparation method of absorbers, the working principle, and detailed insights involving necessary models and mechanisms regarding microwave absorption. It also encapsulates the description of how the ferrite composition, morphology, doping, reflection loss peaks, and matrix account for optimizing the performance of the absorbers. The history, origin, and ancestral use of microwave absorbers are mentioned, and how technological needs lead to advancement in ferrite microwave absorbers has also been discussed. A picture is portrayed of what are microwaves, their potential hazards, and how these hazards should be taken care of with the help of ferrite microwave absorbers. [ABSTRACT FROM AUTHOR]