Photon Field Research Articles

Modelling the variable emission states of γ-ray-emitting narrow-line Seyfert 1 galaxies

ABSTRACT γ-ray-emitting narrow-line Seyfert 1 galaxies (γ-NLS1) constitute an intriguing small population of active galactic nuclei with γ-ray emission resembling low-power flat-spectrum radio quasars (FSRQ), but with differing physical properties. They are jetted, γ/radio-loud Seyfert galaxies, with relatively low black hole masses, accreting at exceptionally high, near-Eddington rates. Certain of these sources exhibit highly variable emission states on relatively short time-scales, the physical origin of which remains elusive. In this work, varying emission states of two bona fide NLS1s, 1H 0323+342 and PMN J0948+0022, and one little-studied FSRQ/intermediate object, B2 0954+25A, are examined. For each source, we analysed quasi-simultaneous multiwavelength data for different states of γ-ray activity and present the results of their broad-band emission modelling, taking into account all available physical constraints to limit the range of the model parameters. Two different scenarios are discussed, in the framework of a one-zone leptonic model, where the high-energy emission is due to the inverse Compton scattering of the disc and broad line region (BLR) or torus photons by relativistic electrons within the jet. The transition from low to high state is well described by variations of the jet parameters, leaving the external photon fields unchanged. The parameterization favours an emission scenario with particle injection on a stationary shock inside the jet. When considering all physical constraints, the disc and BLR scenario is preferred for all three sources. We use the multi-epoch modelling to characterize total jet powers and discuss the intrinsic nature of γ-NLS1 galaxies and FSRQs.

Tunnel Junction Engineered Photocarrier Dynamics in Epitaxial Semiconductor Nanowires for Efficient and Ultrafast Photoelectrochemical Photodetectors

Photodetection using photoelectrochemical (PEC) principles is an emerging field in photonics. In recent years, using epitaxial III-nitride nanowires as photoelectrodes, high-performance PEC-type photodetectors (PDs) have been demonstrated, making the epitaxial III-nitride nanowires a scalable, high-performance PEC-PD architecture. Despite the progress, the photodetection performance improvement mainly occurs through incorporating photocatalysts into the nanowire photoelectrodes. In this study, we show that a semiconductor tunnel junction (TJ), which can be a natural component in the epitaxy process of semiconductor nanowires, can drastically improve the photodetection performance of such nanowire-based PEC-PDs. By using a three-electrode PEC cell configuration, we clearly show that an n++-GaN/InGaN/p++-GaN TJ can lead to a factor of 9× improvement on the responsivity of the InGaN nanowire photoelectrode in the blue band due to the TJ-induced photocarrier dynamics tuning, compared to the InGaN nanowire photoelectrode without the TJ. More drastically, the TJ also improves the photoresponse speed of the nanowire photoelectrode by 2 orders of magnitude, and for the electrode with the TJ an ultrafast response time of less than 10 ms is estimated. This TJ concept can also be applied to other TJ structures for other band photodetections. This study therefore sheds new light on further improving the performance of emerging epitaxial nanowire-based PEC-PDs for a wide range of applications from sensing to information processing.

Near-zero-index platform in photonics: tutorial

The need for miniaturization and faster communications resulted in the rise of photonics, with the big promise of light circuits with high speed and low heating. Near-zero-index materials have gained attention due to their peculiar electromagnetic properties, such as enhancement of the electric field and extraordinary transmission inside photonic waveguides. Furthermore, in such a medium, light propagates with constant phase, thus holding great promise for the field of quantum photonics, where information is preserved instead of degraded by the environment, causing decoherence. However, its realization still remains challenging, as it requires very specific geometries to fulfill some requirements related to the effective medium theory. In this tutorial, we present a theoretical overview of low-index materials’ most intriguing yet useful characteristics and their prospective applications.

Deep Learning-based Inverse Design of the Complete Photonic Band Gap in Two-Dimensional Photonic Crystals

Background: With the continuous development of computer science, data-driven computing methods have shown their advantages in various fields. In the field of photonics, deep learning (DL) can be used to inversely design the structure of optical devices. Objective: The two-dimensional (2D) photonic crystal (PCs) with adjustable structural parameters and a large complete photonic band gap (CPBG) are inversely designed in terms of DL neural network (NN) tagged to obtain a specified width of CPBG. Methods: The new PCs structure is designed by combining multiple factors that produce a CPBG. Tandem networks are used to speed up the training of the NN and tackle the problem of nonuniqueness that arises in inverse design. Results: After various attempts and improvements, the ideal PCs structure was obtained. It is found that the connecting channel between the primitives in the PCs unit cell has a dominate effect on the CPBG. The use of a tandem network enables better convergence of the network. Finally, suitable NN can be obtained, which can realize the forward prediction of the CPBG and the inverse design of the structure. Conclusion: DL can realize forward prediction and inverse design of 2D PCs targeting the width of the CPBG, which broadens the application scope of DL in the field of PCs.

Nonlinear optical properties of PVD-grown Cr2Te3 film and its nonlinear switching application

Recently, two-dimensional (2D) nanomaterials have been investigated extensively in the field of nonlinear photonics. Cr2Te3, which is one of the 2D transition metal chalcogenides, has garnered attention in the field of spintronics and optoelectronics because of its fascinating magnetic and optical properties. Despite its potential in optoelectronics, Cr2Te3 has rarely been studied in the field of nonlinear photonics. This study investigates the nonlinear optical responses of nanoscale-layered Cr2Te3 films grown by physical vapor deposition at telecommunication wavelengths. A large nonlinear absorption coefficient of –(1.43 ± 0.06) × 105 cm/GW and a nonlinear refractive index of –1.22 ± 0.04 cm2/GW at 1560 nm obtained through Z-scan measurements indicate that the Cr2Te3 film shows saturable absorption and self-defocusing properties at telecommunication wavelengths. Density functional theory calculation show that Cr2Te3 is suitable for broadband optical device. The potential of the nanoscale-layered Cr2Te3 film as a base medium for a nonlinear optical switch was evaluated by fabricating a saturable absorption mirror (SAM). Stable Q-switched pulses with a maximum repetition rate of 33.35 kHz and minimum temporal width of 2.62 μs were readily achieved from a fiber laser cavity incorporating the SAM.

Experimental Realization of Topologically‐Protected All‐Optical Logic Gates Based on Silicon Photonic Crystal Slabs

AbstractAs the field of topological photonics has developed over the past 10 years, it has been proven that the combination of topology and photons is very beneficial to the design of robust optical devices against some disturbances. However, most of the work on robust optical logic devices stays at the theoretical level. There are very few topologically‐protected logic devices fabricated in experiments. Here, the experimental fabrication of a series of topologically‐protected all‐optical logic gates is reported. Seven topologically‐protected all‐optical logic gates (OR, XOR, NOT, XNOR, NAND, NOR, and AND) are fabricated on silicon photonic platforms, which show strong robustness even if some disorders exist. These robust logic devices are potentially applicable in future optical signal processing and computing applications.

Characterization of Nanometric Thin Films with Far‐Field Light

AbstractThe characterization of ultrathin transparent films is paramount for various optoelectronic materials, coatings, and photonics. However, characterizing such thin layers is difficult and it requires specialized clean‐room equipment and trained personnel. Here, a contact‐less, all‐optical method is introduced and validated for characterizing nanometric transparent films using far‐field optics. A series of nanometric, smooth, and homogeneous layered samples are fabricated first, alternating transparent spacer and fluorescent layers in a controlled manner. Fluorescence radiation pattern originating from the thin fluorophore layers is then recorded and analyzed and quantitative image analysis is used to perform in operando measurements of the refractive index, film homogeneity and to estimate axial fluorophore distances at a sub‐wavelength scale with a precision of a few of nanometers. The results compare favorably to measurements obtained through more complicated and involved techniques. Applications in nanometrology and biological axial super‐resolution imaging are presented. It is demonstrated in live cells the precise axial localization of single organelles in cortical astrocytes, an important type of brain cell. The approach is cheap, versatile and it will have applications in various fields of photonics.

Excitation wavelength-dependent ultrafast THz emission from surface and bulk of three-dimensional topological insulators

Three-dimensional topological insulators possess various interesting properties that are promising for various modern applications, including in the recently emerging fields of ultrafast THz photonics and spintronics. Their gapless spin-momentum-locked topological surface states with the presence of chiral spin structure are relevant for the development of light helicity-sensitive THz emitters and detectors. In this paper, we report femtosecond excitation pulse wavelength and helicity-dependent response of Bi2Te3 and Bi2Se3 for an enhanced broadband THz pulse emission from the surface and bulk states. Specifically, the excitation wavelength has been varied in a large range from near UV to near IR, where it was observed that the photoexcitation at shorter wavelengths enhances the THz emission from both the surface and bulk states but more rapidly from the surface states. These results will be highly relevant for developing chirality-sensitive efficient THz emitters and detectors.

International Comparison Exercise for Biological Dosimetry after Exposures with Neutrons Performed at Two Irradiation Facilities as Part of the BALANCE Project

In the case of a radiological or nuclear event, biological dosimetry can be an important tool to support clinical decision-making. During a nuclear event, individuals might be exposed to a mixed field of neutrons and photons. The composition of the field and the neutron energy spectrum influence the degree of damage to the chromosomes. During the transatlantic BALANCE project, an exposure similar to a Hiroshima-like device at a distance of 1.5 km from the epicenter was simulated, and biological dosimetry based on dicentric chromosomes was performed to evaluate the participants ability to discover unknown doses and to test the influence of differences in neutron spectra. In a first step, calibration curves were established by irradiating blood samples with 5 doses in the range of 0–4 Gy at two different facilities in Germany (Physikalisch-Technische Bundesanstalt [PTB]) and the USA (the Columbia IND Neutron Facility [CINF]). The samples were sent to eight participating laboratories from the RENEB network and dicentric chromosomes were scored by each participant. Next, blood samples were irradiated with 4 blind doses in each of the two facilities and sent to the participants to provide dose estimates based on the established calibration curves. Manual and semiautomatic scoring of dicentric chromosomes were evaluated for their applicability to neutron exposures. Moreover, the biological effectiveness of the neutrons from the two irradiation facilities was compared. The calibration curves from samples irradiated at CINF showed a 1.4 times higher biological effectiveness compared to samples irradiated at PTB. For manual scoring of dicentric chromosomes, the doses of the test samples were mostly successfully resolved based on the calibration curves established during the project. For semiautomatic scoring, the dose estimation for the test samples was less successful. Doses >2 Gy in the calibration curves revealed nonlinear associations between dose and dispersion index of the dicentric counts, especially for manual scoring. The differences in the biological effectiveness between the irradiation facilities suggested that the neutron energy spectrum can have a strong impact on the dicentric counts.

Nanoscale architecture for frequency-resolving single-photon detectors

Single photon detectors play a key role across several basic science and technology applications. While progress has been made in improving performance, single photon detectors that can maintain high performance while also resolving the photon frequency are still lacking. By means of quantum simulations, we show that nanoscale elements cooperatively interacting with the photon field in a photodetector architecture allow to simultaneously achieve high efficiency, low jitter, and high frequency resolution. We discuss how such cooperative interactions are essential to reach this performance regime, analyzing the factors that impact performance and trade-offs between metrics. We illustrate the potential performance for frequency resolution over a 1 eV bandwidth in the visible range, indicating near perfect detection efficiency, jitter of a few hundred femtoseconds, and frequency resolution of tens of meV. Finally, a potential physical realization of such an architecture is presented based on carbon nanotubes functionalized with quantum dots.

Growth of single-crystals and microstructures using benzothiadiazole derivatives for efficient optical waveguide and nonlinearity

Organic nanomaterials have been extensively studied for the applications of the electronic and photonic fields. The bottom-up fabrication through self-assembly provides a powerful strategy to construct the nanostructures. In this work, we synthesized a conjugated molecule, namely, 4-(1-phenyl-1H-1,2,3-triazol-4-yl)benzo[c][1,2,5]thiadiazole (BT-SC), based on benzothiadiazole and benzene moieties bridged by a triazole. Then, a simple solvent-vapor annealing technique was presented to drive the self-assembly of BT-SC into highly uniform microrods or microfibers. The morphology of the self-assembly could be controlled by simply changing the solution concentration. The compound also could be assembled into aligned nanowires by wetting into hard templates of anodic aluminum oxide (AAO). The fabricated microrods showed strong emitter and excellent optical waveguide behaviors excited with a UV laser. Moreover, the microrods displayed nonlinear optical responses of two-photon excited fluorescence and could therefore become building blocks for actual photonic devices.

Electromagnetic wave representation as a superposition of the quantized vector potential field of single photons

Without stating postulates or advancing any hypothesis, we show that a physical representation for the photon results directly from Maxwell’s theory once the vector potential amplitude is normalized at a single photon level. Electromagnetic waves are composed of a superposition of single photon states with circular polarizations, each extended over a wavelength and occupying a specific quantization volume. This representation is valid at any frequency and consequently can be applied for the modeling of advanced devices ranging from X-Rays and UV applications to fiber optics, microwave antennas and radio waves emitters.

Frontiers in photonics spotlight

Highlighting remarkable research output is an important mission of journals and scientists engaged in dissemination. With this spotlight-review we would like to provide visibility to some of the best recent research outputs and stress the pivotal role of their authors in the Photonics field.

Gouy phase of Bessel-Gaussian beams: theory vs. experiment.

It is well-known that the wave of a freely propagating Gaussian beam experiences an additional π phase shift compared to a plane wave. This phase shift, known as the Gouy phase, has significant consequences in, e.g., nonlinear optics, since the nonlinear processes require high peak intensity and phase matching of the focused beams. Hence, determining and controlling the Gouy phase is crucial in many fields of modern optics and photonics. Here, we develop an analytical model for the Gouy phase of long-range Bessel-Gaussian beams obtained by annihilating highly charged optical vortices. The model accounts for the influence of the relevant experimental parameters (topological charge, radius-to-width ratio of the initial ring-shaped beam, and focal length of the Fourier-transforming lens). We find an evolution of the Gouy phase varying nearly linearly with propagation distance and confirm this result experimentally.

A Perspective on Synthetic Dimensions in Photonics

AbstractThe concept of synthetic dimension has recently emerged as a versatile way to overcome limitations in the number of effectively available dimensions by leveraging non‐spatial degrees of freedom to mimic additional geometric ones. In particular, the field of photonics offers a plethora of technological possibilities for controlling photons and their degrees of freedom, such as polarization, frequency, or orbital angular momentum. Consequently, a broad range of higher‐dimensional physical phenomena is already experimentally accessible in lower‐dimensional photonic devices and has been used and celebrated, for instance, for the exploration of topological physics. The field of synthetic dimensions is currently even further boosted due to additional mathematical mapping procedures, which pave the way toward even higher synthetic dimensions or, in the presence of optical nonlinearities, can translate to multi‐particle quantum systems, allowing appealing alternatives for quantum simulation. In this perspective, current experimental approaches for harnessing synthetic dimensions to probe higher‐dimensional physics on various light‐based platforms are summarized and discussed including an outlook on promising future prospects in this field.

Abstract 1388: Non-thermal plasma-activated medium induces ferroptotic cell death by intracellular ferrous iron overload in head and neck cancer

Abstract The notoriously high proliferation rate of cancer cells requires them to constantly deal with the balance adjustment between oxidative stress overload and upregulated protective antioxidant pathways. It puts them in a vulnerable state whenever one piece of this puzzle went out of control. Non-thermal plasma (NTP) is partially ionized gas operated at or around body temperature and has emerged as a new potential anti-cancer therapy due to its ability to release and induce ROS, RNS, and other free radicals as well as generate UV- photon and electromagnetic field; but the specific mechanism and its specificity to cancer cell are still controversial. Using transcriptomic analysis, we previously reported the link between NTP-activated media (NTPAM)and apoptosis; but the sequencing data also revealed a strong Ferroptotic response in all the 6Head and Neck cancer cell lines we checked. Ferroptosis is a newly identified oxidative-regulated cell death, characterized by the iron-dependent generation of lipid peroxidation. In this study, we found the prolonged treatment of NTPAM-induced cell death via the non-canonical ferroptosis pathway by directly increasing intracellular toxic ferrous Iron (Fe2+). We found that the excessive overexpression of HMOX1 under prolonged NTPAM-induced oxidative stress was actually responsible for the surge of intracellular Fe2+ due to the increase of heme degradation. Pharmacological inhibition or RNA silencing of HMOX1 was able to rescue 2 HNC cell lines from NTPAM-induced increased Iron concentration as well as ferroptosis cell death, both in vivo and in vitro. These results suggest NTP directly induces ferroptosis via an increase of Fe2+ concentration by triggering the over-responding of the NRF2 - HMOX1 antioxidant system. This finding could be exploited to develop future NTP-based cancer therapy as well as in combination with other Iron sensitive anti-neoplastic agents; and could be a potential method of overcoming conventional cancer treatment resistance. Citation Format: QuocKhanh Nguyen, Chan Oh, Seung-Nam Jung, Yudan Piao, Mi Ae Lim, Young Il Kim, Yanli Jin, Hae Jong Kim, Bon Seok Koo. Non-thermal plasma-activated medium induces ferroptotic cell death by intracellular ferrous iron overload in head and neck cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1388.

Guest Editorial Orbital Angular Momentum Photonics

The thirty-six papers in this special issue focus on orbital angular momentum photonics. It is well known that angular momentum carried by elementary particles can be categorized as spin angular momentum (SAM) and orbital angular momentum (OAM). Since the early 1900's, Poynting recognized that a particle, such as a photon, can carry SAM, which has only two possible states. However, only recently, in 1992, Allen et al. discovered that photons with helical phase fronts can carry OAM, which has infinite orthogonal states. Since its discovery, the OAM-carrying beam has gained increasing interest from many different research communities, including physics, chemistry, and engineering, enabling tremendous advances in fundamental theories, devices, and applications. Due to its unique characteristics, OAM Photonics has opened new possibilities in various applications, including micromanipulation, laser beam machining, nonlinear matter interactions, imaging, sensing, quantum cryptography and, classical communications. During the past decade OAM Photonics has grown tremendously, and the field has turned out to be an extremely prosperous research area. This Special Issue provides a snapshot on the latest state of the art for the OAM Photonics field.

Reshaping Strategy at Ultrahigh Strain Rates Enables Large‐Scale Fabrication of Sharp Nanostructures

AbstractMetal nanostructures are the primary component of metamaterials and plasmonics, whereas the high‐throughput production of high‐resolution nanostructures has always been a challenge. Inspired by the special hardening behavior of nanometals at ultrahigh strain rates, a reshaping strategy of hardened structures for large‐scale fabrication of ultra‐sharp nanostructures is proposed in this study. At ultrahigh strain rates, the extreme shear deformation‐induced solid state amorphization and grain‐refining effects of nanometals are first revealed, which provide the required mechanical properties and structural stability for the reshaping of primary structures. The experimental results demonstrate that nanostructures with sub‐10 nm resolution are formed using the reshaping strategy. Additionally, the pressure dependence of deformation behavior of the hardened structures in the ultrahigh‐strain‐rate reshaping process is further explored to guide the nanofabrication process. The results demonstrate that the reshaping strategy at ultrahigh strain rates allows the ultrafine shaping of nanostructures with sub‐10 nm resolution on low‐pressure and submicron‐sized molds, compared with conventional imprinting processes. The generated nanostructures using reshaping process exhibit excellent surface Raman enhancement, enabling high‐sensitivity molecular detection. The reshaping strategy provides a novel strategy for the rapid, repeatable, and economical manufacturing of sharp nanostructures, which has broad application prospects in the fields of plasmonics and photonics.

Non-Hermitian control of confined optical skyrmions in microcavities formed by photonic spin–orbit coupling

Optical skyrmions formed by photonic spin–orbit (SO) coupling are of significant interest in high-dimensional optical information processing. We report the formation mechanism and non-Hermitian properties of skyrmion-like states in a circular confinement potential with photonic SO coupling, which is preferably realized in a concave-planar microcavity system. We show that the effective photonic gauge field leads to two split manifolds of degenerate skyrmions whose spin textures can be controlled via the non-Hermitian properties by introducing circularly polarized gain and loss, exhibiting dramatically discrepant evolutions at the two sides of the exceptional point (EP). Furthermore, the lifetime degeneracy can be lifted by spatially inhomogeneous pumping according to the non-Hermitian mechanism, enabling the possibility for the skyrmion laser. By introducing shape asymmetry of the confinement potential, a double EP evolution can be achieved, which allows non-Hermitian control of the SO coupled states with higher degrees of freedom. These results open the way for the non-Hermitian control of photonic spin in confined systems, which would be of great significance for the fundamentals of advanced optical information processing.

Sol–Gel Photonic Glasses: From Material to Application

In this review, we present a short overview of the development of sol-gel glasses for application in the field of photonics, with a focus on some of the most interesting results obtained by our group and collaborators in that area. Our main attention is devoted to silicate glasses of different compositions, which are characterized by specific optical and spectroscopic properties for various applications, ranging from luminescent systems to light-confining structures and memristors. In particular, the roles of rare-earth doping, matrix composition, the densification process and the fabrication protocol on the structural, optical and spectroscopic properties of the developed photonic systems are discussed through appropriate examples. Some achievements in the fabrication of oxide sol-gel optical waveguides and of micro- and nanostructures for the confinement of light are also briefly discussed.