High Photon Yield Research Articles

High-Power Terahertz Free Electron Laser via Tapering-Enhanced Superradiance

A superradiant FEL in the THz (3 THz) region is currently operating at Ariel University. It is based on the novel ORGAD accelerator, which is a hybrid linear RF photo-cathode 6 MeV electron gun. The hybrid term stands for its unique standing wave (SW)—traveling wave (TW) structure. The undulator generates spontaneous superradiance, which corresponds to spontaneous emission when the electron bunch duration is shorter than the radiated frequency, resulting in a much higher photon yield. However, the efficiency of this scheme is still quite low. In order to achieve higher emission (by improved efficiency), we intend to implement a new and promising radiative interaction scheme: tapering-enhanced superradiance (TES). This particular undulator design employs a tapered (amplitude) undulator in the zero-slippage condition to obtain a significantly more powerful and efficient THz radiation source. At the current stage, the scheme is designed for emission at approximately 0.5 THz. The design and start-to-end simulations demonstrate significant enhancement of superradiant energy and extraction efficiency using this method compared to a reference uniform case.

Accelerated MINFLUX Nanoscopy, through Spontaneously Fast-Blinking Fluorophores.

The introduction of MINFLUX nanoscopy allows single molecules to be localized with one nanometer precision in as little as one millisecond. However, current applications have so far focused on increasing this precision by optimizing photon collection, rather than minimizing the localization time. Concurrently, commonly used fluorescent switches are specifically designed for stochastic methods (e.g., STORM), optimized for a high photon yield and rather long on-times (tens of milliseconds). Here, accelerated MINFLUX nanoscopy with up to a 30-fold gain in localization speed is presented. The improvement is attained by designing spontaneously blinking fluorescent markers with remarkably fast on-times, down to 1-3ms, matching the iterative localization process used in a MINFLUX microscope. This design utilizes a silicon rhodamine amide core, shifting the spirocyclization equilibrium toward an uncharged closed form at physiological conditions and imparting intact live cell permeability, modified with a fused (benzo)thiophene spirolactam fragment. The best candidate for MINFLUX microscopy (also suitable for STORM imaging) is selected through detailed characterization of the blinking behavior of single fluorophores, bound to different protein tags. Finally, optimization of the localization routines, customized to the fast blinking times, renders a significant speed improvement on a commercial MINFLUX microscope.

Collimated gamma beams with high peak flux driven by laser-accelerated electrons

Abstract Laser-accelerated electrons are promising in producing gamma-photon beams of high peak flux for the study of nuclear photonics, obtaining copious positrons and exploring photon–photon interaction in vacuum. We report on the experimental generation of brilliant gamma-ray beams with not only high photon yield but also low divergence, based on picosecond laser-accelerated electrons. The 120 J 1 ps laser pulse drives self-modulated wakefield acceleration in a high-density gas jet and generates tens-of-MeV electrons with 26 nC and divergence as small as $1.51{}^{\circ}$ . These collimated electrons produce gamma-ray photons through bremsstrahlung radiation when transversing a high-Z solid target. We design a high-energy-resolution Compton-scattering spectrometer and find that a total photon number of $2.2\times {10}^9$ is captured within an acceptance angle of $1.1{}^{\circ}$ for photon energies up to $16\;\mathrm{MeV}$ . Comparison between the experimental results and Monte Carlo simulations illustrates that the photon beam inherits the small divergence from electrons, corresponding to a total photon number of $2.2\times {10}^{11}$ and a divergence of $7.73{}^{\circ}$ .

Large area LaBr3:Ce crystals read by SiPM arrays with improved timing and temperature gain drift control

Compact X-rays detectors made of 1/2” or 1” :LaBr3:Ce crystals of cubic shape with SiPM array readout have been developed for the FAMU experiment at RIKEN-RAL. The aim is a precise measurement of the proton Zemach radius with incoming muons. Additional applications may be found in medical physics, such as PET, homeland security and gamma-ray astronomy. Due to the high photon yield of LaBr3:Ce it was possible to use a simple readout scheme based on CAEN V1730 digitizers. Detectors, using Hamamatsu S13361 or S14161 arrays, have good FWHM energy resolutions up to 3% (8%) at the Cs137 (Co57) peak, comparing well with the best results obtained with a photomultiplier’s readout. Detailed studies were performed to correct online the drift with temperature of SiPM gain and to reduce the risetime/falltime of detectors’ signals, that increased going from 1/2” to 1” detectors, due to the larger capacity of the used SiPM arrays.

Quasimonochromatic Bright Gamma-ray Generation from Synchronized Compton Scattering via Azimuthal Spatial-Temporal Coupling

High energy photons can be generated via inverse Compton scattering (ICS) in the collision between energetic electrons and intense laser pulse. The development of laser plasma accelerators promises compact and all-optical gamma-ray sources by colliding the electrons from laser wakefield accelerators to its high-power driving pulse reflected by a plasma mirror. However, the law of optical focusing hinders realization of both high photon yield and monochromatic spectrum in this scenario. We propose an azimuthal spatial-temporal convertor that decouples the focal field strength from laser spot size using helical parabolic geometry. It decomposes the driving laser beam into a pulse train of almost identical divergence angle and focal depth, creating synchronized ICS in the optimized linear regime. The scheme resolves the dilemma between high efficiency and narrow energy spread, facilitating the generation of monochromatic gamma-ray using high power lasers beyond relativistic field strengths.

Visualizing Cytoskeleton-Dependent Trafficking of Lipid-Containing Organelles in Drosophila Embryos.

Early Drosophila embryos are large cells containing a vast array of conventional and embryo-specific organelles. During the first three hours of embryogenesis, these organelles undergo dramatic movements powered by actin-based cytoplasmic streaming and motor-driven trafficking along microtubules. The development of a multitude of small, organelle-specific fluorescent probes (FPs) makes it possible to visualize a wide range of different lipid-containing structures in any genotype, allowing live imaging without requiring a genetically encoded fluorophore. This protocol shows how to inject vital dyes and molecular probes into Drosophila embryos to monitor the trafficking of specific organelles by live imaging. This approach is demonstrated by labeling lipid droplets (LDs) and following their bulk movement by particle image velocimetry (PIV). This protocol provides a strategy amenable to the study of other organelles, including lysosomes, mitochondria, yolk vesicles, and the ER, and for tracking the motion of individual LDs along microtubules. Using commercially available dyes brings the benefits of separation into the violet/blue and far-red regions of the spectrum. By multiplex co-labeling of organelles and/or cytoskeletal elements via microinjection, all the genetic resources in Drosophila are available for trafficking studies without the need to introduce fluorescently tagged proteins. Unlike genetically encoded fluorophores, which have low quantum yields and bleach easily, many of the available dyes allow for rapid and simultaneous capture of several channels with high photon yields.

Visualizing Cytoskeleton-Dependent Trafficking of Lipid-Containing Organelles in <em>Drosophila</em> Embryos

Early Drosophila embryos are large cells containing a vast array of conventional and embryo-specific organelles. During the first three hours of embryogenesis, these organelles undergo dramatic movements powered by actin-based cytoplasmic streaming and motor-driven trafficking along microtubules. The development of a multitude of small, organelle-specific fluorescent probes (FPs) makes it possible to visualize a wide range of different lipid-containing structures in any genotype, allowing live imaging without requiring a genetically encoded fluorophore. This protocol shows how to inject vital dyes and molecular probes into Drosophila embryos to monitor the trafficking of specific organelles by live imaging. This approach is demonstrated by labeling lipid droplets (LDs) and following their bulk movement by particle image velocimetry (PIV). This protocol provides a strategy amenable to the study of other organelles, including lysosomes, mitochondria, yolk vesicles, and the ER, and for tracking the motion of individual LDs along microtubules. Using commercially available dyes brings the benefits of separation into the violet/blue and far-red regions of the spectrum. By multiplex co-labeling of organelles and/or cytoskeletal elements via microinjection, all the genetic resources in Drosophila are available for trafficking studies without the need to introduce fluorescently tagged proteins. Unlike genetically encoded fluorophores, which have low quantum yields and bleach easily, many of the available dyes allow for rapid and simultaneous capture of several channels with high photon yields.

Electrically Excited Plasmonic Ultraviolet Light Sources.

The emission of photons from metal-insulator-metal (MIM) nanojunctions through inelastic tunneling of electrically driven electrons is a well-acknowledged approach to develop miniaturized light sources and ultradense photonic instruments. Generally, the existing research in the optimization of electromigrated tunneling junctions is principally centered on the generation of visible and near-infrared lights. This study reports on the near-ultraviolet (NUV, λ ≈ 355nm) light emission from enhanced tunneling of electrons using aluminum nanoelectrodes. Compared to conventional noble metals, the high electron density and low screening of aluminum enable supporting of pronounced local fields at high energies (i.e, ultraviolet (UV)). As the color of light can be straightforwardly determined by the properties of tunneling structures, the exquisite features of aluminum have empowered the fashioning of tunneling devices that are able to effectively sustain plasmons at short wavelengths and emit UV light with high photon yield. This demonstration is a breakthrough in the generation of high-energy beams using electrically excited aluminum tunneling platforms, which promisingly accelerates the implementation of electrically tunable and ultradense UV light sources.

Particle identification at MeV energies in JUNO

JUNO is a multi-purpose neutrino experiment currently under construction in Jiangmen, China. It is primarily aiming to determine the neutrino mass ordering. Moreover, its 20 kt target mass makes it an ideal detector to study neutrinos from various sources, including nuclear reactors, the Earth and its atmosphere, the Sun, and even supernovae. Due to the small cross section of neutrino interactions, the event rate of neutrino experiments is limited. In order to maximize the signal-to-noise ratio, it is extremely important to control the background levels. In this paper we discuss the potential of particle identification in JUNO, its underlying principles and possible areas of application in the experiment. While the presented concepts can be transferred to any large liquid scintillator detector, our methods are evaluated specifically for JUNO and the results are mainly driven by its high optical photon yield of 1,200 photo electrons per MeV of deposited energy. In order to investigate the potential of event discrimination, several event pairings are analysed, i.e. α/β, p/β, e+/e−, and e−/γ. We compare the discrimination performance of advanced analytical techniques based on neural networks and on the topological event reconstruction keeping the standard Gatti filter as a reference. We use the Monte Carlo samples generated in the physically motivated energy intervals. We study the dependence of our cuts on energy, radial position, PMT time resolution, and dark noise. The results show an excellent performance for α/β and p/β with the Gatti method and the neural network. Furthermore, e+/e− and e−/γ can partly be distinguished by means of neural network and topological reconstruction on a statistical basis. Especially in the latter case, the topological method proved very successful.

Soft Lithography for Manufacturing Scalable Perovskite Metasurfaces with Enhanced Emission and Absorption

AbstractOrganic–inorganic hybrid perovskites have emerged in recent years as a promising alternative to silicon solar cells and other optoelectronic devices, mostly due to their high photon yields, long carrier lifetime, adjustable bandgap, and other merits. While patterning photonic nanostructures onto their inorganic counterparts is well established to augment their capabilities, lack of compatibility with conventional lithography techniques hinders the implementation of those principles with perovskites. Hereby, the fabrication of MAPbI3 nanophotonic structures such as nanoscale metasurfaces is demonstrated via soft lithography, a method in which the patterning is done when the perovskite is not fully crystallized, allowing for crystallization within the mold with the end result of facile and unharmful imprinting of sub‐micron features onto perovskite thin films, over large areas and with the potential to scale up in a seamless way. By doing so, a substantial increase in light absorption as well as twofold photoluminescence enhancement from the perovskite thin film is shown. These results are supported by spectral and lifetime measurements. This method is pertinent to many device configurations and can assist in realizing the future of high‐efficiency perovskite‐based devices, including solar cells, LEDs, lasers, and more.

Electron beam and betatron x-ray generation in a hybrid electron accelerator driven by high intensity picosecond laser pulses

We experimentally studied electron beams and synchrotron x-ray radiation generated from the interaction of high-intensity picosecond laser pulses of 1–3 × 1019 W/cm2 with underdense plasmas of 1–8 × 1019 cm−3. Electron beams with maximum energy over 120 MeV, hundreds mrad divergence and tens of nC charge were generated in the experiments. The measured x-ray spectra were fit well with a synchrotron radiation spectrum combination with a bremsstrahlung spectrum. When laser pulses with intensity of 2.38 × 1019 W/cm2 interacting with pure Nitrogen gas with density of 2.35 × 1018 cm−3, we obtained betatron x-ray radiation with critical energy 3–4 keV and photon number up to 1013 photons/Sr per shot, the energy conversion efficiency is about 3 × 10−5. The high photon yield and large energy conversion efficiency are due to large amounts of electrons trapped by self-modulated laser wakefield and mainly accelerated by direct-laser-acceleration mechanism. Such high yield betatron x-ray sources have widely application prospect as backlight or probe in large scale of laser facilities used for high energy density or fusion sciences.

Ce:LaBr3 crystals with SiPM array readout and temperature control for the FAMU experiment at RAL

Compact X-rays detectors made of 1/2′′ Ce:LaBr3 crystals of cubic shape with SiPM array readout have been developed for the FAMU experiment at RIKEN-RAL, to instrument regions of difficult access. Due to the high photon yield of Ce:LaBr3 it was possible to use a simple readout scheme based on CAEN V1730 digitizers, without a dedicated amplification stage. The drift with temperature of SiPM gain was corrected by using CAEN A7885D regulated power supply chips with temperature feedback. Energy resolutions (FWHM) around 3.5% at the 137Cs peak and around 9% at the 57Co peak were obtained.

Infrared plasmonic photodetectors: the emergence of high photon yield toroidal metadevices

Plasmon excitations in metallic nanostructures can decay directly into dynamic electron–hole pairs, exploitable for photocurrent generation. This approach has extensively been employed to develop nanoplasmonic light-sensing devices with significant responsivity and quantum efficiency. Among the devices, infrared plasmonic photodetectors have gained particular interest for their wide range of technological applications, including spectroscopy, biosensing, and surveillance. This Review discusses the fundamentals, recent advances, and trending mechanisms in the understanding and applications of plasmon-enhanced photocurrent generation in nanostructures across the infrared spectrum. By highlighting and comparing the developed techniques, we demonstrate the newly introduced directions toward achieving high photon yield infrared plasmonic photodetection tools. As a promising concept in modern metaphotonics, we present the emergence of toroidal meta-atoms as plasmon-induced carrier generators with unconventionally exquisite properties for designing advanced, rapid, and next-generation plasmonic photodetectors with significantly high responsivity and photocurrent.

On the prospect of CZTSSe-based thin film solar cells for indoor photovoltaic applications: A simulation study

In this work we present the first systematic study on the prospect of Cu2ZnSn(S,Se)4 or CZTSSe-based thin film photovoltaic devices for indoor energy harvesting applications. Based on numerical analysis, we estimate the performance characteristics of the experimentally reported highest-efficiency CZTSSe device when it is operated under a commercially available white light emitting diode (LED). The obtained efficiency of 13.77% and fill factor of 71.05% are both higher than the values reported under AM1.5 solar radiation. The results of our analysis indicate that performance enhancement under indoor condition arises from the enhanced short-circuit current at high intensity and open-circuit voltage at low intensity, which are both related to the high photon yield of the indoor spectrum corresponding to the bandgap of CZTSSe. Further performance enhancement under indoor condition can be achieved using a type-II band alignment, which we have designed and analyzed employing an intrinsic ZnO layer. The enhanced charge separation resulting from built-in-field of the ZnO layer increases the open circuit voltage by as much as 0.17 V, which in effect leads to an overall efficiency of 15.85% when operated under the considered white LED spectrum.

Re-entry blackout elimination and communication performance analysis based on laser-plasma-induced X-ray emission

X-ray communication (XCOM) offers important advantages to both civilian and military space projects. Rapid advance in high-intensity laser interaction with plasma has become a driving force for providing a new X-ray carrier generation based on the laser wakefield acceleration scheme. XCOM has the potential to eliminate RF shielding on the ground and communicate with the re-entry supersonic spacecraft during blackout occurrence. In this process, the plasma sheath is formed around the surface due to air compression and ablation, which blocks the traditional communication signals. In this paper, the hazardous substance was proactively exploited and coupled with the modulated laser. Particle-In-Cell simulation results indicate the ultra-bright controllable X-ray emission with a small angular divergence (0.04 rad×0.03 rad), a tunable X-ray energy range (4.60 keV to 321.48 keV), and high photon yields. Additionally, the data rate of the communication via the X-ray carrier during re-entry was estimated up to ∼20.7 Mbps by considering the transmission model, encoding schemes and photon information efficiency. Combined with an existing or developing X-ray detection technique, this regime can eliminate re-entry blackout and also provide a novel modulated X-ray source to acquire high-rate, low transmit power, and highly secure space-based data links.

Optimization of soft X-ray phase-contrast tomography using a laser wakefield accelerator.

X-ray phase-contrast imaging allows for non-invasive analysis in low-absorbing materials, such as soft tissue. Its application in medical or materials science has yet to be realized on a wider scale due to the requirements on the X-ray source, demanding high flux and small source size. Laser wakefield accelerators generate betatron X-rays fulfilling these criteria and can be suitable sources for phase-contrast imaging. In this work, we present the first phase-contrast images obtained by using ionization injection-based laser wakefield acceleration, which results in a higher photon yield and smoother X-ray beam profile compared to self-injection. A peak photon yield of 1.9 × 1011 ph/sr and a source size of 3 μm were estimated. Furthermore, the current laser parameters produce an X-ray spectrum mainly in the soft X-ray range, in which laser-plasma based phase-contrast imaging had yet to be studied. The phase-contrast images of a Chrysopa lacewing resolve features on the order of 4 μm. These images are further used for a tomographic reconstruction and a volume rendering, showing details on the order of tens of μm.

Focal spot characteristics of Thomson scattering x-ray sources

With the recent rapid development of x-ray imaging using Thomson scattering x-ray sources, there is an increasing demand for knowledge of the focal spot characteristics of this type of light source. This is because imaging quality is closely related to focal spot characteristics. In this paper, an analytical expression of the focal spot size and beam parameters at arbitrary interaction angles is derived. Based on this, the focal spot can be optimized in a straightforward manner by adjusting the laser and electron focusing at a fixed interaction geometry. As the beam focusing increases, a smaller focal spot and a higher photon yield are obtained, while the bandwidth of scattered x rays deteriorates, leading to a compromise of the above three physical parameters. Considering the beam position and time fluctuations, the focal spot will be broadened and the photon yield will be reduced. Using typical beam parameters at the Tsinghua Thomson scattering x-ray source, it is shown that a micrometer-sized focal spot can be easily achieved. The results will help one to develop the x-ray imaging field, especially in micro-computed tomography applications based on Thomson light sources.

Enhancing the photostability of poly(phenylene ethynylene) for single particle studies.

Single molecule fluorescence (SMF) studies on conjugated polymers yield enhanced information on exciton dynamics and on the interplay between polymer conformation/morphology and photophysical behavior. SMF studies, however, demand good signal stability, excellent photostability, and high photon yields (a measure of both photostability and brightness) and thus the development of strategies to help conjugated polymers (CPs) meet these requirements is a topic of great interest. Here, we evaluate the effect of a number of triplet quencher additives on the photostability of a 49-mer long poly(phenylene-ethynylene) conjugated polymer bearing carboxylate side groups (PPE-CO2-49) that is deposited onto 100 nm diameter SiO2 nanoparticles (NPs). The additives tested include ascorbic acid (AA), β-mercaptoethanol (BME), Ni2+, trolox (TX), and a trolox/trolox quinone mixture (TX/TQ), used either with or without an enzymatic oxygen scavenging system (glucose oxidase/catalase, GODCAT). Total internal reflection fluorescence microscopy (TIRFM) studies enabled the determination of the effect of the additives on the rates of photobleaching, the initial intensity, and the total photon output for hundreds of conjugated polymer coated SiO2 nanoparticles monitored in parallel. Addition of the antioxidant/triplet quenchers AA and TX led to a 3-8-fold increase in the number of photons collected as well as an enhancement of the initial emission intensity, consistent with an increase in the duty cycle attributed to the quenching of triplet states. Removal of oxygen led to an impressive 10-15-fold increase in the photostability relative to buffer, implicating reactive oxygen species (ROS) as an important agent in the photodegradation of PPE-CO2-49. Combining AA and TX with GODCAT had a deleterious rather than an additive effect, suggesting that an oxidizing agent is in fact necessary to rescue the polymer from reactive intermediates formed via reaction with AA/TX. β-Mercaptoethanol and Ni2+ were not found to have useful properties toward the photostabilization of PPE-CO2-49. The results of this study provide suitable imaging conditions to conduct single molecule imaging experiments on conjugated polyelectrolytes.

Gaseous flat-panel detector with glass gas electron multiplier coupled with micro-photodiode array

In this study, we propose and demonstrate a novel imaging system, a gaseous flat-panel detector (FPD). The gaseous FPD consists of a glass gas electron multiplier (G-GEM) with a scintillation gas, which is optically coupled with photodiode panel fabricated with liquid crystal display technology. The G-GEM is ideal as a low energy deposition radiation detector because of its single stage high gas-gain and hence, its high photon yield. We obtained a preliminary X-ray image with the system by using a Ne/CF4 90/10 gas mixture. The typical position resolution was 0.93 mm in FWHM, which was obtained from the fitting of edge profiles

Fluorescent Proteins for Super-Resolution Microscopy

Super-resolution fluorescence microscopy is the method of choice to monitor cellular and subcellular biological processes in live cells. Among the different fluorescent labels presently available, fluorescent proteins (FPs) of the GFP family have the key advantage of being genetically encodable. Localization-based super-resolution microscopy approaches require photoactivatable FPs (PA-FPs) that will change their spectral properties upon irradiation with light of a particular wavelength. To be able to distinguish individual, activated fluorophores from the background and to localize them with high precision, a high photon yield in the activated state and a high dynamic range, i.e., the contrast ratio between the fluorescence of the activated (on) and deactivated (off) states, are essential. In stimulated emission depletion (STED) super-resolution microscopy, the sample is raster-scanned by a tightly focused excitation beam followed by a red-shifted, donut-shaped depletion beam. Any FP used for STED must be exquisitely photostable because it has to go through multiple excitation-depletion cycles while the sample is scanned near its location. Moreover, it must be excitable and de-excitable by the lasers that are typically installed in commercial STED microscopes. Therefore, far-red emitting FPs are preferred.We have selected the green-to-red photoconvertible mEosFPthermo and the far-red emitting mGarnet as templates for targeted protein engineering. Considering that FPs are all very similar and share the same scaffold, an obvious strategy was to identify specific amino acid residues that elicit certain properties to one FP and introduce the corresponding amino acid in the other FP variant by using site-directed mutagenesis. As we will show, such simple rational engineering approaches often do not meet with success, which clearly shows that our current understanding of the physics of proteins is far from being complete.