Photon Distribution Research Articles

Photon counting statistics with imperfect detectors

Measurement of photon statistics is an important tool for the verification of quantum properties of light. Due to the various imperfections of real single photon detectors, the observed statistics of photon counts deviates from the underlying statistics of photons. Here we analyze statistical properties of coherent states, and investigate a connection between Poissonian distribution of photons and sub-Poissonian distribution of photon counts due to the detector dead-time corrections. We derive a functional dependence between the mean number of photons and the mean number of photon counts, as well as connection between higher-order statistical moments, for the pulsed or continuous wave coherent light sources, and confirm the results by numerical simulations.

Method and portable bench for tests of the laser optical calibration system components for the Baikal-GVD underwater neutrino Cherenkov telescope

The Large-scale deep underwater Cherenkov neutrino telescopes like Baikal-GVD, ANTARES or KM3NeT, require calibration and testing methods of their optical modules. These methods usually include laser-based systems which allow us to check the telescope responses to the light and for real-time monitoring of the optical parameters of water such as absorption and scattering lengths, which show seasonal changes in natural reservoirs of water. We will present a testing method of a laser calibration system and a set of dedicated tools developed for Baikal-GVD, which includes a specially designed and built, compact, portable, and reconfigurable scanning station. This station is adapted to perform fast quality tests of the underwater laser sets just before their deployment in the telescope structure, even on ice, without a darkroom. The testing procedure includes the energy stability test of the laser device, 3D scan of the light emission from the diffuser and attenuation test of the optical elements of the laser calibration system. The test bench consists primarily of an automatic mechanical scanner with a movable Si detector, beam splitter with a reference Si detector and, optionally, Q-switched diode-pumped solid-state laser used for laboratory scans of the diffusers. The presented test bench enables a 3D scan of the light emission from diffusers, which are designed to obtain the isotropic distribution of photons around the point of emission. The results of the measurement can be easily shown on a 3D plot immediately after the test and may be also implemented to a dedicated program simulating photons propagation in water, which allows us to check the quality of the diffuser in the scale of the Baikal-GVD telescope geometry.

Charged and neutral {overline{B}}_{u,d,s} \u2192 \u03b3 form factors from light cone sum rules at NLO

We present the first analytic mathcal{O}left({alpha}_sright) -computation at twist-1,2 of the {overline{B}}_{u,d,s} → γ form factors within the framework of sum rules on the light-cone. These form factors describe the charged decay {overline{B}}_uto gamma {mathrm{ell}}^{-}overline{v} , contribute to the flavour changing neutral currents {overline{B}}_{d,s}to gamma {mathrm{ell}}^{+}{mathrm{ell}}^{-} and serve as inputs to more complicated processes. We provide a fit in terms of a z-expansion with correlation matrix and extrapolate the form factors to the kinematic endpoint by using the gBB*γ couplings as a constraint. Analytic results are available in terms of multiple polylogarithms in the supplementary material. We give binned predictions for the {overline{B}}_uto gamma {mathrm{ell}}^{-}overline{v} branching ratio along with the associated correlation matrix. By comparing with three SCET-computations we extract the inverse moment B-meson distribution amplitude parameter λB = 360(110) MeV. The uncertainty thereof could be improved by a more dedicated analysis. In passing, we extend the photon distribution amplitude to include quark mass corrections with a prescription for the magnetic vacuum susceptibility, χq, compatible with the twist-expansion. The values χq = 3.21(15) GeV−2 and χs = 3.79(17) GeV−2 are obtained.

Theory and Analysis of Single-Molecule FRET Experiments.

Inter-dye distances and conformational dynamics can be studied using single-molecule FRET measurements. We consider two approaches to analyze sequences of photons with recorded photon colors and arrival times. The first approach is based on FRET efficiency histograms obtained from binned photon sequences. The experimental histograms are compared with the theoretical histograms obtained using the joint distribution of acceptor and donor photons or the Gaussian approximation. In the second approach, a photon sequence is analyzed without binning. The parameters of a model describing conformational dynamics are found by maximizing the appropriate likelihood function. The first approach is simpler, while the second one is more accurate, especially when the population of species is small and transition rates are fast. The likelihood-based analysis as well as the recoloring method has the advantage that diffusion of molecules through the laser focus can be rigorously handled.

Horizontal position reconstruction in PandaX-II

Dual-phase noble-gas time projection chambers (TPCs) have improved the sensitivities for dark matter direct search in past decades. The capability of TPCs to reconstruct 3-D vertexes of keV scale recoilings is one of the most advantageous features. In this work, we develop two horizontal position reconstruction algorithms for the PandaX-II dark matter search experiment using the dual-phase liquid xenon TPC. Both algorithms are optimized by the 83mKr calibration events and use photon distribution of ionization signals among photomultiplier tubes to infer the positions. According to the events coming from the gate electrode, the uncertainties in the horizontal positions are 3.4 mm (3.9 mm) in the analytical (simulation-based) algorithm for an ionization signal with several thousand photon electrons in the center of the TPC.

Two-step spatially offset Raman spectroscopy technique for rapid and non-invasive detection of drugs in containers—simulation and experiment

Spatially offset Raman spectroscopy (SORS) provides a new powerful method for non-invasive detecting of the substance in containers. However, it takes a long time to collect spectra at different offset distances and needs multivariate analysis, which is not suitable for rapid on-site detection. In this paper, a rapid two-step SORS detection method based on the Raman scattering photons transmission and distribution simulated by Monte Carlo is proposed. Commonly used packaging materials such as plastic and glass are considered, the ‘plastic/glass-drug’ double-layer samples were constructed and the Raman intensities of each layer of samples at different offset distances were simulated. The Raman spectra of actual samples at different offset distances were collected by a self-developed portable confocal Raman spectrometer with additional collection probe. The relationship between the optimal offset distance of two-step SORS and the thickness of different materials container wall was investigated. Actual measurement results are consistent with simulation results. The feasibility of decreasing the detection steps and shortening the detection time by pre-selecting the optimal offset distance was studied. Based on this, we propose the two-step SORS technique that only needs to collect spectra at two pre-selected locations with a simple data processing method to quickly obtain the Raman spectrum of the substance in the container. Two-step SORS technique can greatly reduce the detection steps, improve the detection efficiency, and achieve non-invasive rapid detection.

UNO SGUARDO ALL’INTERNO DEL CORPO UMANO: LA SPETTROSCOPIA OTTICA TEMPO RISOLTA PER LA DIAGNOSTICA CLINICA NON-INVASIVA

Diffuse optics studies the propagation of light in highly scattering media (e.g. biological tissues). Time-resolved techniques – which measure the time-of-flight distribution of photons in the medium – permit to separate the contribution of absorption (linked to chemical composition) from scattering (produced by microstructure). Furthermore, for increasing photon time-of-flight, larger tissue depths are reached. These two properties, combined with the intrinsic non-invasiveness of the technique, are very interesting for clinical applications, such as diagnosis of breast cancer, imaging of brain activity, monitoring the functional and metabolic state of biological tissues in depth. The technology has undergone impressive growth, moving from laboratory laser systems to miniature wearable devices. To grant the reliability of the information obtained in vivo, international collaboration is needed to set objective validation protocols, in view of a growing diffusion of the method, from clinical diagnostics to home care.

Novel pre-burst stage of gamma-ray bursts from machine learning

Gamma-ray bursts (GRBs), as extremely energetic explosions in the universe, are widely believed to consist of two stages: the prompt phase and the subsequent afterglow. Recent studies indicate that some high-energy photons are emitted earlier at source than the prompt phase. Due to the light speed variation, these high-energy photons travel more slowly than the low-energy photons, so that they are observed after the prompt low-energy photons at the detector. Based on the data from the Fermi Gamma-ray Space Telescope (FGST), we analyse the photon distribution before the prompt emission in detail and propose the existence of a hitherto unknown pre-burst stage of GRBs by adopting a classification method of machine learning. Analysis on the photons automatically selected by machine learning also produces a light speed variation at ELV=3.55×1017GeV.

Joint Optimization of Photon-Carbon Ion Treatments for Glioblastoma.

Carbon ions are radiobiologically more effective than photons and are beneficial for treating radioresistant gross tumor volumes (GTV). However, owing to a reduced fractionation effect, they may be disadvantageous for treating infiltrative tumors, in which healthy tissue inside the clinical target volume (CTV) must be protected through fractionation. This work addresses the question: What is the ideal combined photon-carbon ion fluence distribution for treating infiltrative tumors given a specific fraction allocation between photons and carbon ions? We present a method to simultaneously optimize sequentially delivered intensity modulated photon (IMRT) and carbon ion (CIRT) treatments based on cumulative biological effect, incorporating both the variable relative biological effect of carbon ions and the fractionation effect within the linear quadratic model. The method is demonstrated for 6 glioblastoma patients in comparison with the current clinical standard of independently optimized CIRT-IMRT plans. Compared with the reference plan, joint optimization strategies yield inhomogeneous photon and carbon ion dose distributions that cumulatively deliver a homogeneous biological effect distribution. In the optimal distributions, the dose to CTV is mostly delivered by photons and carbon ions are restricted to the GTV with variations depending on tumor size and location. Improvements in conformity of high-dose regions are reflected by a mean EQD2 reduction of 3.29 ± 1.22 Gy in a dose fall-off margin around the CTV. Carbon ions may deliver higher doses to the center of the GTV, and photon contributions are increased at interfaces with CTV and critical structures. This results in a mean EQD2 reduction of 8.3 ± 2.28 Gy, in which the brain stem abuts the target volumes. We have developed a biophysical model to optimize combined photon-carbon ion treatments. For 6 glioblastoma patient cases, we show that our approach results in a more targeted application of carbon ions that (1) reduces dose in normal tissues within the target volume, which can only be protected through fractionation; and (2) boosts central target volume regions to reduce integral dose. Joint optimization of IMRT-CIRT treatments enable the exploration of a new spectrum of plans that can better address physical and radiobiological treatment planning challenges.

Reconstruction of the laser Compton scattered gamma-ray distribution in the energy-angle phase space from crystal diffraction data

The distribution of laser Compton scattered (LCS) photons in the energy-angle phase space reflects the parameters of the laser and electron beams at the collision point and provides the spectral density and bandwidth available in the LCS source. Diagnosis of the energy-angle phase space is thus crucial for developing high-flux and narrow-bandwidth LCS sources. Such diagnosis has been utilized for photon energies below 100 keV, but not realized for photon energies above 1 MeV. We demonstrated reconstruction of the energy-angle phase space distribution of an LCS photon beam at an energy of 1.7 MeV by utilizing photon diffraction with a silicon mosaic crystal and a silicon comb crystal, both of which have enlarged integrated reflectivity. The reconstructed photon distribution is well reproduced by numerical simulations. The demonstrated diagnostic technique is an efficient tool for the development of LCS photon sources and is beneficial to the use of existing LCS facilities.

Resonant Scattering of Plane‐Wave and Twisted Photons at the Gamma Factory

AbstractA theoretical investigation of the resonant elastic scattering of laser photons by ultra‐relativistic partially stripped ions, that is the core process of the Gamma Factory project, is presented. Special emphasis in the study is placed on the angular distribution and polarization of scattered photons as observed in the collider and ion‐rest reference frames. In order to describe these (angular and polarization) properties for arbitrary relativistic many‐electron ion, the general approach, based on the application of irreducible polarization tensors, is laid down. By making use of the polarization tensors, the scattering of both conventional plane‐wave‐ and twisted (or vortex) photons is explored in detail. For the former case, it is shown how the propagation directions and polarization states of incident and outgoing photons are related to each other for the , , and resonant transitions. For the scattering of initially twisted light that carries non‐zero orbital angular momentum, the angular distribution of secondary photons is explored and the conditions under which they are also twisted are discussed.

Photonic hook generated by the Janus microcylinder under point-source illumination

A photonic hook (PH) is a high-intensity, curved focusing beam with a subwavelength waist based on the photonic nanojet effect. It is generally created by illuminating mesoscale transparent particles using optical plane waves. In this work, we numerically explore the generation of the PH supported by the Janus microcylinder under point-source illumination. To simulate the photonic intensity distributions near the shadow surface of the Janus microcylinder, a finite-difference time-domain technique is used. The power flow distributions near the Janus microcylinder are examined for working in the visible spectrum. Due to the asymmetric vortices of Poynting vectors, the PH with a large bending angle can be produced. By changing the location of the point-source illumination, the shape and curvature of the PH can be adjusted efficiently. Moreover, when the point-source illumination is located close to the Janus microcylinder, a long focal length PH can be present. Based on the numerical results, we propose a practical modeling scheme for optical imaging using a microscope where the light source is close to the target.

Magnetic dipole moments of the Zc(4020)+ , Zc(4200)+ , Zcs(4000)+ and Zcs(4220)+ states in light-cone QCD

The magnetic dipole moments of the $Z_{c}(4020)^+$, $Z_{c}(4200)^+$, $Z_{cs}(4000)^{+}$ and $Z_{cs}(4220)^{+}$ states are extracted in the framework of the light-cone QCD sum rules. In the calculations, we use the hadronic molecular form of interpolating currents, and photon distribution amplitudes to get the magnetic dipole moment of $Z_{c}(4020)^+$, $Z_{c}(4200)^+$, $Z_{cs}(4000)^{+}$ and $Z_{cs}(4220)^{+}$ tetraquark states. The magnetic dipole moments are obtained as $\mu_{Z_{c}} = 0.66^{+0.27}_{-0.25}$, $\mu_{Z^{1}_{c}}=1.03^{+0.32}_{-0.29}$, $\mu_{Z_{cs}}=0.73^{+0.28}_{-0.26}$, $\mu_{Z^1_{cs}}=0.77^{+0.27}_{-0.25}$ for the $Z_{c}(4020)^+$, $Z_{c}(4200)^+$, $Z_{cs}(4000)^{+}$ and $Z_{cs}(4220)^{+}$ states, respectively. We observe that the results obtained for the $Z_{c}(4020)^+$, $Z_{c}(4200)^+$, $Z_{cs}(4000)^{+}$ and $Z_{cs}(4220)^{+}$ states are large enough to be measured experimentally. As a by product, we predict the magnetic dipole moments of the neutral $Z_{cs}(4000)$ and $Z_{cs}(4220)$ states. The results presented here can serve to be helpful knowledge in experimental as well as theoretical studies of the properties of hidden-charm tetraquark states with and without strangeness.

Lepton pair production in ultraperipheral collisions

The lepton pair production in ultraperipheral collisions is studied in the classical field approximation. We derive a general form of the cross section in terms of photon distributions that depend on the transverse momentum and coordinate based on the wave packet form of nuclear wave functions. Such a general form of the cross section in the classical field approximation contains the results of the generalized equivalent photon approximation (EPA) as well as the corrections beyond EPA in the Born approximation. By rewriting the general form of the cross section in light-cone coordinates, we find a good connection with the transverse momentum dependent distribution factorization formalism in the Born approximation. Our numerical results are consistent with current experimental data.

Imprints of high-momentum nucleons in nuclei on hard photons from heavy-ion collisions near the Fermi energy

The short-range correlation (SRC) induced by the tensor force in the isosinglet neutron-proton interaction channel leads to a high-momentum tail (HMT) in the single-nucleon momentum distributions n(k) in nuclei. Owing to the remaining uncertainties about the tensor force, the shape of the nucleon HMT may be significantly different from the dilute interacting Fermi gas model prediction $n(k) \sim1/k^4$ similar to the HMT in cold atoms near the unitary limit. Within an isospin- and momentum-dependent Boltzmann-Uehling-Uhlenbeck transport model incorporating approximately the nucleon HMT, we investigate hard photon emissions in $^{14}$N+$^{12}$C and $^{48}$Ca+$^{124}$Sn reactions at beam energies around the Fermi energy. Imprints of different shapes of the HMT on the energy spectrum, angular distribution and transverse momentum spectrum of hard photons are studied. While the angular distribution does not carry any information about the shape of the nucleon HMT, the energy spectra and especially the mid-rapidity transverse momentum spectra of hard photons are found to bare strong imprints of the shapes of nucleon HMTs in the two colliding nuclei.

Specific features of radiation emitted upon tunnel ionisation of atoms in extremely intense laser fields

Radiation emitted by fast electrons in the process of multiple tunnel ionisation of heavy atoms in the focus of a laser pulse with extreme intensity exceeding 1022 W cm−2 is studied. It is shown that the spectral-angular distribution of emitted photons in a wide range of angles is qualitatively determined by relations of the synchrotron radiation theory. The dependences of the number and the characteristic frequency of emitted photons on the laser pulse parameters are estimated. The obtained results can be used to determine the maximum laser intensity in the focus.

Simplified derivation of the Kompaneets equation

An isotropic electromagnetic field in a plasma of thermalized electrons undergoes changes in energy as a result of Compton scattering and an Einstein–Hopf drag force on the electrons, eventually approaching a Bose–Einstein photon distribution at the electron temperature. The rate of change of field energy due to the combined effects of Compton scattering and the drag force is shown to be described by the Kompaneets equation for photon diffusion in frequency space. A similarity is noted between this approach and Einstein's derivation of the Planck spectrum based on the recoil of atoms as they absorb and emit radiation.

Comparative analysis of the coordinated motion of Hsp70s from different organelles observed by single-molecule three-color FRET

Cellular function depends on the correct folding of proteins inside the cell. Heat-shock proteins 70 (Hsp70s), being among the first molecular chaperones binding to nascently translated proteins, aid in protein folding and transport. They undergo large, coordinated intra- and interdomain structural rearrangements mediated by allosteric interactions. Here, we applied a three-color single-molecule Förster resonance energy transfer (FRET) combined with three-color photon distribution analysis to compare the conformational cycle of the Hsp70 chaperones DnaK, Ssc1, and BiP. By capturing three distances simultaneously, we can identify coordinated structural changes during the functional cycle. Besides the known conformations of the Hsp70s with docked domains and open lid and undocked domains with closed lid, we observed additional intermediate conformations and distance broadening, suggesting flexibility of the Hsp70s in adopting the states in a coordinated fashion. Interestingly, the difference of this distance broadening varied between DnaK, Ssc1, and BiP. Study of their conformational cycle in the presence of substrate peptide and nucleotide exchange factors strengthened the observation of additional conformational intermediates, with BiP showing coordinated changes more clearly compared to DnaK and Ssc1. Additionally, DnaK and BiP were found to differ in their selectivity for nucleotide analogs, suggesting variability in the recognition mechanism of their nucleotide-binding domains for the different nucleotides. By using three-color FRET, we overcome the limitations of the usual single-distance approach in single-molecule FRET, allowing us to characterize the conformational space of proteins in higher detail.

Machine Learning for Time-Resolved Emission: Image Resolution Enhancement

Abstract This article describes a novel method for improving image resolution achieved using time-resolved photon emission techniques. Instead of directly generating images from photon counting, all detected photons are displayed as a point cloud in 3D space and a new higher-resolution image is generated based on probability density functions associated with photon distributions. Unsupervised learning algorithms identify photon distribution patterns as well as fainter emission sources.

A muon-track reconstruction exploiting stochastic losses for large-scale Cherenkov detectors

IceCube is a cubic-kilometer Cherenkov telescope operating at the South Pole. The main goal of IceCube is the detection of astrophysical neutrinos and the identification of their sources. High-energy muon neutrinos are observed via the secondary muons produced in charge current interactions with nuclei in the ice. Currently, the best performing muon track directional reconstruction is based on a maximum likelihood method using the arrival time distribution of Cherenkov photons registered by the experiment's photomultipliers. A known systematic shortcoming of the prevailing method is to assume a continuous energy loss along the muon track. However at energies >1 TeV the light yield from muons is dominated by stochastic showers. This paper discusses a generalized ansatz where the expected arrival time distribution is parametrized by a stochastic muon energy loss pattern. This more realistic parametrization of the loss profile leads to an improvement of the muon angular resolution of up to 20% for through-going tracks and up to a factor 2 for starting tracks over existing algorithms. Additionally, the procedure to estimate the directional reconstruction uncertainty has been improved to be more robust against numerical errors.