Coherent Absorption Research Articles

Dose increment in ultrashort particle irradiations via coherent stopping power

We present a relativistic self-consistent theory of the coherent stopping power (CSP) of ultradense charged particle beams propagating in a dense matter. CSP corresponds to a collective inelastic collision which adds to the ordinary stopping power of individual particles. Unlike the latter, which depends only on the particles' energy, CSP depends upon many more parameters such as the total charge of the ensemble and its charge density and shape. This paves the way for a broad variety of novel methods to tailor particle absorption and penetration in a dense matter. CSP losses can be explained both by collective excitations of single or multiple molecules and by the emission of coherent Cherenkov radiation. Here we demonstrate that the former mechanism is more relevant than the latter. We find that the coherent energy absorption of subpicosecond particle bunches in water occurs exciting a broad Debye process in the GHz range and an intermolecular stretching vibration mode in the THz region. We generalize the Bethe-Bloch stopping power formula to coherent effects including self-forces, dielectric screening, and absorption by the dense matter. For the sake of a self-consistent dynamical theory including phase space evolution, we have also generalized the Fermi-Eyges theory of particle diffusion to the presence of forces. Nonlinear dynamics is demonstrated, inducing nonlinear dose release, beam self-focusing, and self-enhancement of coherent losses. Given the advent of ultraintense particle sources and their use for biomedical and other relevant applications, our results may be of paramount importance for contemporary and future developments of science and technology. Published by the American Physical Society 2024

Coherent emission and attosecond transient absorption of N+2 in strong fields

Coherent emission and attosecond transient absorption of N+2 in strong fields

Three-dimensional detection of CO2 and wind using a 1.57 µm coherent differential absorption lidar

A 1.57-µm coherent differential absorption lidar is demonstrated for measuring three-dimensional CO2 and wind fields simultaneously. The maximum detection range of CO2 is up to 6 km with a range resolution of 120 m and a time resolution of 1 min. A preliminary assessment of instrument performance is made with a 1-week continuous observation. The CO2 concentration over a column from 1920 to 2040 m is compared with the one measured by an optical cavity ring-down spectrometer placed on a 2 km-away meteorological tower. The concentration is strongly correlated with the in-situ spectrometer with a correlation coefficient and RMSE of 0.91 and 5.24 ppm. The measurement accuracy of CO2 is specified with a mean and standard deviation of 2.05 ppm and 7.18 ppm, respectively. The regional CO2 concentration and the three-dimensional wind fields are obtained through different scanning modes. Further analysis is conducted on vertical mixing and horizontal transport of CO2 by combining with the measured wind fields.

Dual-Band All-Optical Logic Gates by Coherent Absorption in an Amorphous Silicon Graphene Metasurface.

The dual-band polarization-independent all-optical logic gate by coherent absorption effect in an amorphous silicon (a-Si) graphene metasurface is investigated theoretically and numerically. Taking the substrate effect into consideration, the coherent perfect absorption condition of the a-Si graphene metasurface is derived on the basis of the Cartesian multipole method. The coherent nearly perfect absorption of the a-Si graphene metasurface is realized by the interference of multipole moments and the interband transition of monolayer graphene, achieving peak values of 91% and 92% at 894.5 nm and 991.5 nm, respectively. The polarization independence of the coherent absorption is revealed due to the center symmetry of the structure of the a-Si graphene metasurface. The dual-band polarization-independent all-optical XOR and OR logic gates are implemented at 894.5 nm and 991.5 nm by the a-Si graphene metasurface based on the coherent nearly perfect absorption, which has the opportunity to be utilized in all-optical computing, all-optical data processing, and future all-optical networks.

Arithmetic logic unit based on the metastructure with coherent absorption: erratum.

We present a corrigendum to our Letter [Opt. Lett.48, 5699 (2023)10.1364/OL.505761]. In section 3 of the original supplementary material, the absolute value is incorrectly taken in resolving the Kubo formula for describing the conductivity of graphene. Because this is a mistake with the conductivity of graphene, the coupling of the original structure is broken when the correct result is inserted into the code of the transfer matrix. So, the structure of the arithmetic logic unit (ALU), characteristic frequency point, and phase control have been modified accordingly. However, the ultimate function and the conclusion of this work remain unchanged.

Spatio-spectral control of coherent nanophotonics

Abstract Fast modulation of optical signals that carry multidimensional information in the form of wavelength, phase or polarization has fueled an explosion of interest in integrated photonics. This interest however masks a significant challenge which is that independent modulation of multi-wavelength carrier signals in a single waveguide is not trivial. Such challenge is attributed to the longitudinal direction of guided-mode propagation, limiting the spatial separation and modulation of electric-field. Here, we overcome this using a single photonic element that utilizes active coherent (near) perfect absorption. We make use of standing wave patterns to exploit the spatial-degrees-of-freedom of in-plane modes and individually address elements according to their mode number. By combining the concept of coherent absorption in spatio-spectral domain with active phase-change nanoantennas, we engineer and test an integrated, reconfigurable and multi-spectral modulator operating within a single element. Our approach demonstrates for the first time, a non-volatile, wavelength-addressable element, providing a pathway for exploring the tunable capabilities in both spatial and spectral domains of coherent nanophotonics.

Dynamically manipulation of anisotropic coherent perfect absorption in borophene metasurface

This paper proposed a borophene-based metamaterial device to achieve the anisotropic coherent perfect absorption (CPA) effect in the two-port device. By simply adjusting the polarization angle of the incident light, the dynamic switching of the CPA resonance peak wavelength can be achieved. Besides, by simultaneously modulating the electron doping concentration of borophene and the relative phase of the incident light, the coherent absorption efficiency of borophene can be continuous modulated for both polarization directions. Furthermore, the theorem of scattering matrix is utilized to elucidate the physical mechanism of CPA, and the analytical results demonstrate remarkable accordance with the numerical computations. Owing to the flexible continuous tunability, the proposed borophene CPA device is expected to open up new opportunities for optical modulators and all-optical logic chips.

Acoustic coherent perfect absorption based on a PT symmetric coupled Mie resonator system

Parity-time (PT) symmetric coupled resonator systems have exhibited intriguing and unexpected properties in optics and electronics. Here, we extend it to acoustics and report a coupled Mie resonators (MRs) system respecting PT symmetry. The system is constructed with two parallel waveguides connected by an aperture and two MRs placed symmetrically at both sides of the aperture. Instead of using active elements or complex refractive index modulation without gain, we exploit the incident waves of the waveguide as an effective gain so that PT symmetry with balanced loss and gain is realized by only passive materials. Coherent perfect absorption (CPA), which can completely absorb the in-phase excitations with the same intensity provided from two opposite directions, is observed in the PT symmetric phase and at the exceptional point but not in the broken phase. In addition, by varying the relative phase between the two incident waves, the coherent absorption can be tuned from CPA to zero. Our design may provide a flexible platform to research PT symmetry in acoustics and may have applications in tunable noise control, acoustic modulators, and switches.

Arithmetic logic unit based on the metastructure with coherent absorption.

An arithmetic logic unit (ALU) based on the metastructure (MS) with coherent absorption (CA) is proposed in this Letter. The ALU can perform AND and exclusive OR logical operations at the same frequency point. So it can be regarded as an optical half-adder. By controlling the chemical potential of graphene and the phase difference of coherent electromagnetic waves (EWs), two different binary numbers are input into the ALU. The dynamic absorption peaks, which are generated based on the CA, output the outcomes of the carry-digit bit and non-carry sum bit. This ALU can be used in the field of optical processing and encryption, such as processing hamming code. This given ALU based on the MS with CA has major implications for advancing the study and investigation into the application of CA. Furthermore, it also provides a new, to the best of our knowledge, idea for the study of MS with logical operation.

Theoretical proposal of a sensor based on the comb-shaped coherent absorption realized by the magnetized plasma photonic crystals

The study presents a theoretical framework outlining a sensor capable of realizing comb-shaped coherent absorption peaks in magnetized plasma photonic crystals. The proposed model enables simultaneous measurement of alterations in the applied magnetic induction intensity, thickness of the dielectric layer, incident angle of electromagnetic waves, and the refractive index. The nascent stage of coherent absorption theory's application to photonic crystals is currently under scrutiny. Enabling interaction between both forward and backward propagating electromagnetic waves at either end of the photonic crystals creates comb-shaped absorption peaks for detecting variances in physical quantities. The sensor model utilized the transfer matrix method for computation of the transmission and reflection coefficients, linear range, sensitivity, and further linear fitting equations across all physical quantities when employed for multi-physics measurements. The present study entailed an analysis of linear range, the figure of merit, and the sensitivity of a sensor designed to detect magnetic induction intensity. Results demonstrate that the linear range from 0.7 T–1.3 T, while the figure of merit equals 50.2189 T⁻1 and sensitivity equals 4.3535 × 10⁻8 (ωd/2πc)/T. Conversely, when measuring thickness, the corresponding linear range extends from 0.4–0.85 mm, with figure of merit reaching 481.06 mm⁻1 and sensitivity equating to 3.5567 × 10⁻4 (ωd/2πc)/mm. Additionally, the sensor's application to the measurement of both incident angle and refractive index revealed parameters for linear range that ranged from 2 to 4.1, while figure of merit was calculated at 124.00 RIU⁻1 and sensitivity at 15.54952 (ωd/2πc)/RIU. Regarding incident angle, related values for linear range spanned from 15°–44°, with figure of merit established at 4.2157°⁻1 and sensitivity at 0.8661 (ωd/2πc)/degree.

Inverse design of omnidirectional coherent absorbers for optical power beaming applications.

An efficient photovoltaic power converter is a critical element in laser power beaming systems for maximizing the end-to-end power transfer efficiency while minimizing beam reflections from the receiver for safety considerations. We designed a multilayer absorber that can efficiently trap monochromatic light from broad incident angles. The proposed design is built on the concept of a one-way coherent absorber with inverse-designed aperiodic multilayer front- and back-reflectors that enable maximal optical absorption in a thin-film photovoltaic material for broad angles. We argue that the broad bandwidth is achieved through an optimization search process that automatically engineers the modal content of the cavity to create multiple overlapping resonant modes at the desired angle or frequency range. A realistic design is provided based on GaAs thin films with inverse-designed multilayer binary AlAs/AlGaAs mirrors. The proposed device can pave the way for efficient optical power beaming systems.

Coherent Control of Wave Beams Via Unidirectional Evanescent Modes Excitation

AbstractConventional coherent absorption occurs only when two incident beams exhibit mirror symmetry with respect to the absorbing surface, i.e., the two beams have the same incident angles, phases, and amplitudes. This study proposes a more general metasurface paradigm for coherent perfect absorption with impinging waves from arbitrary asymmetric directions. By exploiting excitation of unidirectional evanescent waves, the output can be fixed at one reflection direction for any amplitude and phase of the control wave. It shows theoretically and confirm experimentally that the relative amplitude of the reflected wave can be tuned continuously from zero to unity by changing the phase difference between the two beams, i.e., switching from coherent perfect absorption to full reflection. It hopes that this study will open up promising possibilities for wave manipulation via evanescent waves engineering with applications in optical switches, optical computing, one‐side sensing, photovoltaics, and radar cross‐section control.

Adaptive measurement filter: efficient strategy for optimal estimation of quantum Markov chains

Continuous-time measurements are instrumental for a multitude of tasks in quantum engineering and quantum control, including the estimation of dynamical parameters of open quantum systems monitored through the environment. However, such measurements do not extract the maximum amount of information available in the output state, so finding alternative optimal measurement strategies is a major open problem. In this paper we solve this problem in the setting of discrete-time input-output quantum Markov chains. We present an efficient algorithm for optimal estimation of one-dimensional dynamical parameters which consists of an iterative procedure for updating a `measurement filter' operator and determining successive measurement bases for the output units. A key ingredient of the scheme is the use of a coherent quantum absorber as a way to post-process the output after the interaction with the system. This is designed adaptively such that the joint system and absorber stationary state is pure at a reference parameter value. The scheme offers an exciting prospect for optimal continuous-time adaptive measurements, but more work is needed to find realistic practical implementations.

Single-Photon-Compatible Telecommunications-Band Quantum Memory in a Hot Atomic Gas

Tomorrow's quantum Internet will be powered by light and will work over today's telecommunication infrastructure, so we need low-noise, high-bandwidth, telecom-band quantum optical memory to enable scaling in the presence of loss and quantum operations. The authors have built such a device, using coherent two-photon absorption in warm rubidium vapor. This quantum memory stores gigahertz-bandwidth telecom-band light pulses with mean photon number less than one, and retrieves them with a signal-to-noise ratio exceeding 10${}^{4}$. This makes possible ultrahigh-fidelity storage of single-photon qubits and is compatible with quantum-dot light sources, for hybridized quantum photonic networking.

Photon number resolution without optical mode multiplication

Abstract Common methods to achieve photon number resolution rely on fast on-off single-photon detectors in conjunction with temporal or spatial mode multiplexing. Yet, these methods suffer from an inherent trade-off between the efficiency of photon number discrimination and photon detection rate. Here, we introduce a method of photon number resolving detection that overcomes these limitations by replacing mode multiplexing with coherent absorption of a single optical mode in a distributed detector array. Distributed coherent absorption ensures complete and uniform absorption of light among the constituent detectors, enabling fast and efficient photon number resolution. As a proof-of-concept, we consider the case of a distributed array of superconducting nanowire single-photon detectors with realistic parameters and show that deterministic absorption and arbitrarily high photon number discrimination efficiency can be achieved by increasing the number of detectors in the array. Photon number resolution without optical mode multiplication provides a simple yet effective method to discriminate an arbitrary number of photons in large arrays of on-off detectors or in smaller arrays of mode multiplexed detectors.

Theory, design and characterization of metamaterial absorbers: a formal assessment

Metamaterial (MTM) absorbers and their design have been of prime interest in view of their capability to absorb electromagnetic waves of high frequencies. Different types of MTM absorbers have been reported in the last two decades. Keeping this in view an attempt was made to review the progress of MTM absorbers in terms of the theory behind them, designing and construction. This paper reviewed the basic theory and design regulations of a perfect MTM absorber at high, narrow and broad band frequencies. Also we reviewed tunable frequency and coherent absorbers. This exercise was done to focus on recent developments in metamaterial absorbers and present the tested results in a more precise way

Optically tunable and broadband terahertz coherent perfect absorption based on coupled toroidal dipole excitation

ABSTRACT In this paper, we present a multiple dumbbell-shaped aperture metasurface (MDSAM) combined semiconductors to force implementation of tunable broadband coherent perfect absorption (CPA) in the terahertz (THz) region, thus manipulating the interaction between electromagnetic wave and matter. Utilizing the variation of phase difference between two back-propagation beams, on the one hand, the coherent absorptivity at 2.73–4.04 THz can be tailored successively from greater than 90% to as low as 11.7%. On the other hand, exciting the semiconductor germanium (Ge) through a pump power, the realization of quadruple-band, dual-band, and broadband CPA switching is demonstrated. Numerical simulations reveal that the CPA of the reported MDSAM is attributed to the destructive interference originating from two anti-parallel toroidal dipole moments. Our findings offer a novel platform to design tunable broadband CPA and comprehend the underlying mechanism with electromagnetic response for toroidal dipole.

Commissioning of the cryogenic sample environment for the TARUMÃ station at the CARNAÚBA beamline at Sirius/LNLS

TARUMÃ is a multi-technique station at CARNAÚBA (Coherent X-Ray Nanoprobe Beamline) at the 4th-generation light source Sirius at the Brazilian Synchrotron Light Laboratory (LNLS). With a tender-to-hard energy range from 2.05 to 15 keV and a fully coherent nanoprobe focused via an all-achromatic KB (Kirkpatrick-Baez) optics, it can be used for simultaneous multiple nanoscale X-ray techniques in 2D and 3D. This includes ptychography coherent diffraction imaging (ptycho-CDI), absorption spectroscopy (XAS), diffraction (XRD), fluorescence (XRF) and luminescence (XEOL). In particular, the tender energies can be used to study light elements that are commonly present in soft biological samples, ensuring the unique position of the station in the Life and Environmental Sciences program at LNLS. Still, enabling this range of experiments is sometimes only possible with cryogenically cooled samples as the high beam dose can result in both chemical and structural damage at ambient temperature conditions. At TARUMÃ, to comply with the heavily occupied volume around the sample and the sample positioning architecture, this is enabled by an open-atmosphere cryogenic system based on a commercial cryojet and a custom-designed sample holder. Following a predictive engineering approach, the system is capable of conditioning the sample down to 155K, whilst avoiding icing and condensation in nearby instrumentation and preserving the nanometer-level positioning requirements of the scanning station. Here we present the commissioning results of the referred system along with the first beamline measurements.

Bidirectional Acoustic Negative Refraction Based on a Pair of Identical Purely Imaginary Metamaterials Slabs

Acoustic purely imaginary metamaterials (PIMs) slabs can support the coexistence of coherent perfect absorption and laser modes and are used to achieve negative refraction. Previous works have focused on a pair of different PIM slabs, one operating in CPA mode and the other in laser mode. However, this structure has restrictions on the incident wave direction, specifically the wave can only be incident from the CPA side. In this paper, we derive the analytical expressions for the parameters required for the coexistence of CPA and laser modes in acoustic PIM slabs. Numerical simulation results show that such PIM slab can freely switch states between the coherent complete absorber and the laser depending on the incidence direction. On this basis, by using a pair of identical PIM slabs, bidirectional negative refraction and planar focusing can be achieved. In addition, the parameters in the appropriate range can be found by adjusting the mode order, which facilitates the experimental verification. So far, the required acoustic purely imaginary metamaterials (PIMs) have not been experimentally demonstrated, and the results presented in the manuscript are theoretical speculations on their existence, so practical applications may require more sophisticated design and engineering.

Ultra-broadband coherent perfect absorption via elements with linear phase response

Increasing interest in perfect absorption of metasurface has initiated a discussion on the implementation of ultra-broadband coherent perfect absorption (CPA). Here, we present a mirror symmetric coherent absorption metasurface (CAMS) with polarization independence based on resistive thin films and annular metal patterns to force the fulfillment of ultra-broadband CPA in terahertz (THz) regime, controlling the interplay between electromagnetic waves and matter. By incorporating internal and external ring-shaped films with attached phase-delay lines, the desired phase response can be obtained, laying the foundation for implementing ultra-broadband coherent absorption. Simultaneously, by building a metal-medium composite structure superseding the dielectric substrate, additional promotion of the coherent absorptivity over the operation frequencies is realized. Manipulating the phase difference of two back-propagation coherent beams, the coherent absorptivity at 8.34-25.07 THz can be tailored successively from over 95.7% to as low as 38.1%. Moreover, with the incident angle up to 70° for the transverse electric wave, the coherent absorptivity is still over 74.8% from 8.34 THz to 25.07 THz. And for the transverse magnetic wave, at 6.67-24.2 THz, above 81.3% coherent absorptivity is visible with the incident angle increased from 0° to 60°. Our finding provides an interesting approach to designing ultra-broadband coherent absorption devices and may serve applications in THz modulators, all-optical switches, and signal processors.