We describe a laser–plasma platform for photon–photon collision experiments to measure fundamental quantum electrodynamic processes. As an example we describe using this platform to attempt to ...observe the linear Breit–Wheeler process. The platform has been developed using the Gemini laser facility at the Rutherford Appleton Laboratory. A laser Wakefield accelerator and a bremsstrahlung convertor are used to generate a collimated beam of photons with energies of hundreds of MeV, that collide with keV x-ray photons generated by a laser heated plasma target. To detect the pairs generated by the photon–photon collisions, a magnetic transport system has been developed which directs the pairs onto scintillation-based and hybrid silicon pixel single particle detectors (SPDs). We present commissioning results from an experimental campaign using this laser–plasma platform for photon–photon physics, demonstrating successful generation of both photon sources, characterisation of the magnetic transport system and calibration of the SPDs, and discuss the feasibility of this platform for the observation of the Breit–Wheeler process. The design of the platform will also serve as the basis for the investigation of strong-field quantum electrodynamic processes such as the nonlinear Breit–Wheeler and the Trident process, or eventually, photon–photon scattering.
We present a single-photon avalanche diode (SPAD) developed in 55 nm bipolar-CMOS-DMOS (BCD) technology, which achieves high photon detection probability (PDP) while its breakdown voltage is lower ...than 20 V. To enhance the PDP performance, the SPAD junction is optimized with lightly-doped-drain and high-voltage-well layers which are provided in the BCD process. In addition, the dielectric layers over the SPAD are properly etched to reduce multilayer reflections so that the photon collection efficiency can be maximized. The SPAD achieves a peak PDP of 89.4% at 450 nm wavelength with the excess bias voltage of 7 V, while its breakdown voltage is 16.1 V. At the same bias condition, the device shows a dark count rate (DCR) of 38.2 cps/μm 2 . It also achieves a timing jitter of 55 ps at 940 nm with the 7 V excess bias. This new high-performance SPAD implemented in such an advanced node BCD technology operating at a low breakdown voltage is expected to have a major impact on several single-photon applications, especially biomedical sensing and imaging.
Covalent organic frameworks (COFs) have emerged as potential light emitting polymers for optoelectronic and optical devices, but their nonlinear optical properties, particularly two‐photon absorption ...and fluorescence (TPA/TPF), have seldom been explored. Herein, to construct octupolar three‐branched modules (e.g., acceptor 3‐(donor‐core), triphenylbenzene core) within a 2D cyano‐sp2c‐conjugated framework is proposed that results in two‐photon luminescent COFs, combining a large TPA cross section and high quantum yield (QY). Such octupolar module‐embedded sp2c‐conjugated COFs emit not only intense one‐photon fluorescence with QY of 27.2% in the solid state and 38.1% in tetrahydrofuran—superior to almost all reported COFs, but also efficient two‐photon fluorescence with large TPA cross section of 1225 GM—remarkably surpassing the corresponding cyano‐sp2c‐linked model compounds (104 GM). The finding highlights the synergy between sp2c‐conjugated framework and octupolar modules that leads to markedly improved TPA response owing to extended conjugated length, enhanced planarity and multidimensional intramolecular interaction. In view of the versatility of the branched chromophore, the proposed design idea is expected to be used to exploit more two‐photon active COF materials for a range of applications. Multiple uses of the COF in information encryption and warm white light‐emitting diodes are also exemplified.
Octupolar three‐branched modules embedded in a 2D cyano‐sp2c‐conjugated framework enable two‐photon luminescent covalent organic frameworks (COFs) combining a large two‐photon absorption cross section of 1225 GM and intense one‐photon fluorescence with a quantum yield of 27.2% in solid state and 38.1% in tetrahydrofuran—superior to almost all reported COFs, which can be used in information encryption and warm white light‐emitting diodes.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
We derive the full expression for the shape of the charge spectrum that results from the illumination of a photo-multiplier tube. The derivation is for low intensity illumination with constant gain, ...a common condition for most nuclear and particle physics applications. Under these conditions, it is shown that an analytic expression can be formulated that describes details of the spectrum including the pedestal and dark noise with excellent fidelity to allow statistical fits to data. The derivation and full formula using either Gaussian or Poisson models for gain, and its limiting forms under various simplifying assumptions are presented with strategies on their use. The analytic description can be used to formulate data acquisition strategies to perform precise absolute calibration of photo-multipliers, the digitizers, and the data acquisition system.
In this work, we report the performance of InGaAs/InAlAs single photon avalanche photodiodes (SPADs) with different structures for X-ray photon-counting applications. Combined with the high-speed ...sinusoidally gated quenching technique, InGaAs/InAlAs SPADs with a short dead time and low dark counting rate ( DCR ) achieve a high X-ray photon count rate. A maximum photon count rate of 12 Mcps has been obtained with a 2 GHz repetition frequency at the highest X-ray fluxes. The counting system is close to a non-paralyzable model with a dead time of 56 ns and the linear response count rate is up to 4.1 Mcps (active diameter is 50 μm) at 50 keV, which is suitable for operating in high fluence rates (10 6 -10 9 photons/s/mm 2 ) for clinical CT imaging. Therefore, our results may provide a new approach to improve the performance of X-ray photon-counting detectors.
Two‐photon polymerization (2PP) represents a powerful technique for the fabrication of precise three‐dimensional structures on a micro‐ and nanometer scale for various applications. While many review ...articles are focusing on the used polymeric materials and their application in 2PP, in this review the class of two‐photon photo initiators (2PI) used for radical polymerization is discussed in detail. Because the demand for highly efficient 2PI has increased in the last decades, different approaches in designing new efficient 2PIs occurred. This review summarizes the 2PIs known in literature and discusses their absorption behavior under one‐ and two‐photon absorption (2PA) conditions, their two‐photon cross sections (σTPA) as well as their efficiency under 2PP conditions. Here, the photo initiators are grouped depending on their chromophore system (D‐π‐A‐π‐D, D‐π‐D, etc.). Their polymerization efficiencies are evaluated by fabrication windows (FW) depending on different laser intensities and writing speeds.
Two‐photon polymerization has established itself as one of the most important techniques for the fabrication of 3D structures in the micro to nanometer range. To ensure precise and rapid fabrication, photo initiators (PI) are used that have been specially developed for this purpose. In this review article, the PIs known to the literature are listed and compared in particular according to their structural elements, fabrication behavior and two‐photon cross‐section.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Modern signal and image acquisition systems used in the field of cardiology acquire, analyze, and store data digitally. Surface electrocardiography, intra-cardiac electrogram recording, ...echocardiograms, x-ray, magnetic resonance imaging, and computed tomography are among the modalities in the cardiology field where signal processing is applied. Digital signal processing techniques allow us to automate many of the analyses that had previously been done manually with greater precision, accuracy and speed, as well as detect features and patterns in data that may be too subtle to observe by eye. As more cardiologists are becoming more reliant on such technology, a basic understanding of digital signals and the techniques used to extract information from these signals are required. TOC:Section 1: Basic signal processing and techniques: Digital signals and images.-Differentiation and integration.-Signal averaging.-Data compression.-Frequency domain.-Wavelets.-Pattern matching.- Section 2: Applications to clinical cardiology: Surface ECG.-Intra-cardiac electrograms.-Echocardiogram.-CT and MRI.-The catheterization lab.-Nuclear cardiology.-Holter monitoring.
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FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Although for photon Bose-Einstein condensates the main mechanism of the observed photon-photon interaction has already been identified to be of a thermo-optic nature, its influence on the condensate ...dynamics is still unknown. Here a mean-field description of this effect is derived, which consists of an open-dissipative Schrödinger equation for the condensate wave function coupled to a diffusion equation for the temperature of the dye solution. With this system at hand, the lowest-lying collective modes of a harmonically trapped photon Bose-Einstein condensate are calculated analytically via a linear stability analysis. As a result, the collective frequencies and, thus, the strength of the effective photon-photon interaction turn out to strongly depend on the thermal diffusion in the cavity mirrors. In particular, a breakdown of the Kohn theorem is predicted, i.e. the frequency of the centre-of-mass oscillation is reduced due to the thermo-optic photon-photon interaction.
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