Photon Counting Method Research Articles

Effective and robust quantum state tomography of electron-nuclear spins in diamond by time-resolved fluorescence

Quantum state tomography (QST) of electron-nuclear spins of nitrogen-vacancy (NV) center in diamond commonly requires a sequence of population flipping operations and frequent calibration of basis states by fluorescence photon-counting. Here, we realize an effective and robust quantum state tomography of electron-nuclear spins based on time-resolved fluorescence, which can enhance the signal-to-noise ratio between different basis states up to 29.6% compared to the photon-counting method. Meanwhile, our method can directly obtain the population of four basis states with only one measurement, which significantly improves the efficiency of tomography. Furthermore, the photon count rate fluctuation of time-resolved fluorescence can be reduced to the standard quantum limit by normalization operation, indicating that the time-resolved method is calibration-free. This method could be easily applied to multi-nuclear spins of NV center in diamond and extended to other solid-state spin systems.

The effect of the degree of hydration of aluminium oxide thin films on the afterglow luminescence phenomena

The occurrence of afterglow luminescence in aluminum oxide thin films obtained by non-electrolytic aluminum oxide conversion coating has been proved. The kinetic parameters of luminescence decay and its spectral distribution were determined using the single photon counting method. The obtained samples of hydrated aluminum oxide, supported on metallic aluminum, were subjected to dehydration and dehydroxylation. The process of dehydroxylation led to a significant (by over two orders of magnitude) increase in the efficiency of afterglow luminescence. On the basis of the luminescence decay spectrum, the emitters in the systems studied were identified to be oxygen vacancies in the structure of Al2O3, including F, F2, F+. Moreover, a high probability of involvement of electrons from the conductivity band and F and F+ states photoconversion in determination of the character of afterglow luminescence was indicated. Durations of afterglow luminescence measured for the barrier layers and porous aluminum oxide films, obtained by electrochemical oxidation, were compared. Significant differences were detected between the kinetic parameters of luminescence decay and the character of emission spectra, whose analysis permitted proposing mechanisms of the processes.

Detection of defect-induced luminescence in epoxy-based insulation materials via phase-resolved photon counting method

Electroluminescence (EL) has shown promise in detecting micro-defects in epoxy-based insulation materials. Understanding the various luminescence mechanisms caused by defects is crucial for improving the characterization and analysis of insulation defects. In light of this, this study proposes a photon counting-based approach to investigate the impact of defects on the entire evolutionary process of the luminescence mechanism. A phase-resolved photon counting (PRPC) method is proposed to examine the polarity and periodicity of photon counting results influenced by defects. Additionally, a simulation model based on the finite element method is established to analyze how defects modify the distribution of electric field and space charges. Observations suggest that the PRPC-based approach holds promise for advancing the defect analysis of epoxy insulation used in gas-insulated equipment.

Time-resolved mid-infrared photoluminescence spectroscopy of an undoped InAs substrate

Time-resolved mid-infrared photoluminescence (PL) spectroscopy of an undoped InAs substrate has been achieved with wavelength upconversion and time-correlated single photon counting methods. The substrate exhibits multiple PL peaks at photon energies of around 0.415 eV, and the peak positions and intensities change as the temperature is varied from 3.7 to 80 K. The dominant PL peaks are attributed to free and donor-bound excitons and radiative recombination between electrons at the Fermi edge in the conduction band and holes in the valence band edge. The PL lifetime of the excitons is 12 ns, which is four times longer than that of GaAs. The band edge electron–hole recombination has a longer PL lifetime of 60 ns at 20 K. The unveiling of luminescence dynamics in narrow bandgap semiconductors will contribute to the development of mid-infrared light-emitting devices.

Relationship of single crystal growth and luminescence properties of Cr-doped gadolinium gallium garnet crystals for radiation dose-rate monitoring systems

For the decommissioning of Fukushima Daiichi Nuclear Plants, a novel real-time dose-rate monitor consisting of a scintillator, 100-m long optical fiber and CCD spectrometer has been proposed, and this scintillation material is required to have an emission wavelength of longer than approximately 650 nm. In this paper, as a candidate material for the system, we focused on Ce/Cr co-doped Gd3Ga5O12 (Ce/Cr:GGG) single crystals grown by the micro-pulling down method. Since the light output of this material was expected to depend on the Cr3+ concentration, we investigated the relationship between Cr segregation and luminescence properties in Ce/Cr:GGG crystal. Generally, a single photon counting method is not available to evaluate its light output accurately due to the long decay time, we used a novel technique “emission-intensity two-dimensional- mapping method” (2D-image method) to verify the light intensity at each point of the sample. This method realized estimation of the light intensity within the sample, though segregation of Cr3+ is observed. The results showed that Cr was concentrated in the center part along the radial direction in the grown crystals, while all parts had an emission wavelength of approximately 730 nm excited by X-ray. Using the 2D-image method, emission intensity was found to correspond to the Cr concentration, and its correlation coefficients between emission intensity and Cr concentration were over 0.8. We found that our material is available for the monitoring system when the Cr dense part of the crystal is cut and used.

High-Flux Fast Photon-Counting 3D Imaging Based on Empirical Depth Error Correction

The time-correlated single-photon-counting (TCSPC) three-dimensional (3D) imaging lidar system has broad application prospects in the field of low-light 3D imaging because of its single-photon detection sensitivity and picoseconds temporal resolution. However, conventional TCSPC systems always limit the echo photon flux to an ultra-low level to obtain high-accuracy depth images, thus needing to spend amounts of acquisition time to accumulate sufficient photon detection events to form a reliable histogram. When the echo photon flux is increased to medium or even high, the data acquisition time can be shortened, but the photon pile-up effect can seriously distort the photon histogram and cause depth errors. To realize high accuracy TCSPC depth imaging with a shorter acquisition time, we propose a high-flux fast photon-counting 3D imaging method based on empirical depth error correction. First, we derive the photon flux estimation formula and calculate the depth error of our photon-counting lidar under different photon fluxes with experimental data. Then, a function correction model between the depth errors and the number of echo photons is established by numerical fitting. Finally, the function correction model is used to correct depth images at high photon flux with different acquisition times. Experimental results show that the empirical error correction method can shorten the image acquisition time by about one order of magnitude while ensuring a moderate accuracy of the depth image.

Development of time-resolved photoluminescence microscopy of semiconductor materials and devices using a compressed sensing approach

Charge carrier lifetime is a key property of semiconductor materials for photonic applications. One of the most established methods for measuring lifetimes is time-resolved photoluminescence (TRPL), which is typically performed as a single-point measurement. In this paper, we demonstrate a new time-correlated single photon counting method (TCSPC) for TRPL microscopy, for which spatial information can be achieved without requiring point-by-point scanning through the use of a compressed sensing (CS) approach. This enables image acquisition with a single pixel detector for mapping the lifetime of semiconductors with high repeatability. The methodology for signal acquisition and image reconstruction was developed and tested through simulations. Effects of noise levels on the reliability and quality of image reconstruction were investigated. Finally, the method was implemented experimentally to demonstrate a proof-of-concept CS TCSPC imaging system for acquiring TRPL maps of semiconductor materials and devices. TRPL imaging results of a semiconductor device acquired using a CS approach are presented and compared with results of TRPL mapping of the same excitation area measured through a point-by-point method. The feasibility of the methodology is demonstrated, the benefits and challenges of the experimental prototype system are presented and discussed.

The effect of laser repetition rate in second harmonic generation imaging and intensity detection

Here we revealed that lasers with lower repetition rates (5 kHz and 50 kHz) from an amplifier were more efficient in SHG imaging than a laser with high repetition rate (80 MHz) from an oscillator, demonstrating that peak power played a more important role than the repetition rate for high SHG yield. Although lasers with relatively high peak power damaged the cancer cells used in the imaging at a relatively lower laser power, better signal/noise ratio was achieved before the occurrence of the adverse damage. It was also revealed that photobleaching was avoided with the lower repetition rate lasers. Furthermore, the three lasers were applied in analyzing the scattered SHG intensity from colloidal BaTiO3 nanoparticles using photon counting method. All tests with the three lasers reached satisfactory results. Importantly, the lasers with low repetition rates showed great potential in the detection of weak nonlinear scattering.

Lensless Three-Dimensional Imaging under Photon-Starved Conditions.

In this paper, we propose a lensless three-dimensional (3D) imaging under photon-starved conditions using diffraction grating and computational photon counting method. In conventional 3D imaging with and without the lens, 3D visualization of objects under photon-starved conditions may be difficult due to lack of photons. To solve this problem, our proposed method uses diffraction grating imaging as lensless 3D imaging and computational photon counting method for 3D visualization of objects under these conditions. In addition, to improve the visual quality of 3D images under severely photon-starved conditions, in this paper, multiple observation photon counting method with advanced statistical estimation such as Bayesian estimation is proposed. Multiple observation photon counting method can estimate the more accurate 3D images by remedying the random errors of photon occurrence because it can increase the samples of photons. To prove the ability of our proposed method, we implement the optical experiments and calculate the peak sidelobe ratio as the performance metric.

Quantum noise spectroscopy as an incoherent imaging problem

I point out the mathematical correspondence between an incoherent imaging model proposed by my group in the study of quantum-inspired superresolution [Tsang, Nair, and Lu, Physical Review X 6, 031033 (2016)] and a noise spectroscopy model also proposed by us [Tsang and Nair, Physical Review A 86, 042115 (2012); Ng et al., Physical Review A 93, 042121 (2016)]. Both can be regarded as random displacement models, where the probability measure for the random displacement depends on unknown parameters. The spatial-mode demultiplexing (SPADE) method proposed for imaging is analogous to the spectral photon counting method proposed in Ng et al. (2016) for optical phase noise spectroscopy -- Both methods are discrete-variable measurements that are superior to direct displacement measurements (direct imaging or homodyne detection) and can achieve the respective quantum limits. Inspired by SPADE, I propose a modification of spectral photon counting when the input field is squeezed -- simply unsqueeze the output field before spectral photon counting. I show that this method is quantum-optimal and far superior to homodyne detection for both parameter estimation and detection, thus solving the open problems in Tsang and Nair (2012) and Ng et al. (2016).

Development of photon counting technique to operate from discrete photons to continuous regime using DAQ card in LabVIEW platform

A sensor like a photomultiplier tube (PMT) has shown many applications, particularly in the photon counting regime, where it generates discrete electrical pulses in response to the input photons. Commercially available photon counters used to count these pulses assuming the incident photons in the discrete form. In general, whenever two or more photons arrive concurrently, the photon counter record it as a single pulse and count it as single count. On the contrary, when continuous photons arrive, the discrete photon counting approach ceases to function, and a continuous capture technique is used to estimate the photons intensity. In this article, a photon-counting method based on a data acquisition card (DAQ Model: Agilent U1071A), which works in the discrete to continuous photon regime where the commercial photon counters stop counting is described. To facilitate the precise counting of the discrete and merged pulses, a program has been developed in LabVIEW incorporating the logic of pulse width and amplitude. The developed technique is tested for its functionality and compared with the commercially available photon counter SR400. The outcomes of the study indicate that the developed system is capable of operating from discrete photons to a continuous regime and has a better dynamic range than the SR400 gated photon counter.

Determination of fluorescence quantum yields and decay times of NADH and FAD in water–alcohol mixtures: The analysis of radiative and nonradiative relaxation pathways

Combined studies on fluorescence quantum yield of coenzymes NADH and FAD in water–methanol, water–ethanol and water–propylene glycol mixtures and on time-resolved fluorescence of these molecules under excitation at 450 and 355 nm by means of time-correlated single photon counting (TCSPC) method have been carried out. A novel model that allowed to separate the contributions from several excited state relaxation mechanisms to fluorescence dynamics in the pico- and nanosecond time domains and to fluorescence quantum yield was developed and used for analysis of experimental data. The results indicated the existence of at least two different nonradiative relaxation mechanisms in NADH and FAD: a relatively slow nanosecond and a much faster picosecond ones. The analysis suggested that the increase of NADH fluorescence quantum yield with all alcohols concentration occurred mainly due to relatively slow nanosecond non-radiative and radiative relaxation mechanisms related with the change of conformation distributions, while the picosecond fluorescence quenching was found to have practically the same and conformation-insensitive value in water–monohydric alcohol mixtures. Similar conclusion was made for NADH in water–propylene glycol solutions where however a moderate decrease of the picosecond quenching rate was determined at high propylene glycol concentrations that was attributed to a slowdown of picosecond quenching under high viscosity conditions. In the case of FAD the analysis suggested that the dramatic rise of fluorescence quantum yield with alcohol concentration was mostly due to the conformation-sensitive picosecond quenching. This conclusion supports the known mechanism of the picosecond fluorescence quenching in FAD through electron transfer reaction in the π-stacked conformation between isoalloxazine and adenine moieties. Radiative decay times in NADH and FAD were estimated from experimental data and found to be about 10 ns and 20–30 ns, respectively.

Computational Photon Counting Using Multithreshold Peak Detection for Fast Fluorescence Lifetime Imaging Microscopy.

Time-resolved photon counting methods have a finite bandwidth that restricts the acquisition speed of techniques like fluorescence lifetime imaging microscopy (FLIM). To enable faster imaging, computational methods can be employed to count photons when the output of a detector is directly digitized at a high sampling rate. Here, we present computational photon counting using a hybrid photodetector in conjunction with multithreshold peak detection to count instances where one or more photons arrive at the detector within the detector response time. This method can be used to distinguish up to five photon counts per digitized point, whereas previous demonstrations of computational photon counting on data acquired with photomultiplier tubes have only counted one photon at a time. We demonstrate in both freely moving C. elegans and a human breast cancer cell line undergoing apoptosis that this novel multithreshold peak detection method can accurately characterize the intensity and fluorescence lifetime of samples producing photon rates up to 223%, higher than previously demonstrated photon counting FLIM systems.

Poly(ethylene oxide) Is Positively Charged in Aqueous Solutions.

There have been controversies about the binding of cations to poly(ethylene oxide) (PEO) chains in aqueous solutions. In the current study, single molecular evidence of charging PEO chains by cation binding in aqueous solutions is provided. From the adoption of the photon-counting histogram method, it is discovered that the local pH value at the vicinity of the PEO chain is higher than the bulk solution, showing that the PEO chain is positively charged. Such a situation exists with and without the presence of salt (NaCl) in the solution, presumably due to the binding of cations, such as hydronium and sodium ions. Single molecular electrophoresis experiments using fluorescence correlation spectroscopy demonstrate that the PEO chains are weakly charged with a charging extent of ~5%. In comparison to the salt-free condition, the addition of external salt (NaCl) at moderate concentrations further charges the chain. The charging causes the PEO chains to expand and a further increase in the salt concentration causes the chain to shrink, exhibiting a polyelectrolyte-like behavior, demonstrated by the hydrodynamic radii of a single PEO chain. The effect of ion identity is discovered with alkali cations, with the order of the charging capacity of Li+ < Na+ < Cs+ < K+.

Temperature-sensitive fluorescence decay kinetics of thioflavin T derivatives in glycerol

Possible use of Thioflavin T based fluorescent molecular rotors as temperature sensors was assessed in this work. Fluorescent properties of Thioflavin T and its derivative 6-Me-BTA-2C in 99% glycerol were studied using steady-state and time-resolved fluorescence spectroscopy methods. For Thioflavin T in glycerol it has been found that temperature growth from 261 K to 353 K results in ~ 3 orders of magnitude increase of non-radiative decay rate constant knr for the excited state of the molecule. Fluorescence decay studies by time-correlated single photon counting method showed that fluorescence decay kinetics of Thioflavin T in glycerol can be used for temperature measurements in the range 260-290 K. For 6-Me-BTA-2C molecule the range of the maximal sensitivity was shifted to higher temperatures (280-320 K). The obtained results about fluorescent properties and decay kinetics of Thioflavin T based dyes in highly viscous media can be used to develop nanoscale temperature sensors. Keywords: temperature sensor, fluorescent molecular rotor, nanothermometry, thioflavin T, TICT.

Температурная зависимость кинетики затухания флуоресценции производных тиофлавина T в глицерине

Possible use of Thioflavin T based fluorescent molecular rotors as temperature sensors was assessed in this work. Fluorescent properties of Thioflavin T and its derivative 6-Me-BTA-2C in 99 % glycerol were studied using steady-state and time-resolved fluorescence spectroscopy methods. For Thioflavin T in glycerol it has been found that temperature growth from 261 K to 353 K results in ~3 orders of magnitude increase of non-radiative decay rate constant k_nr for the excited state of the molecule. Fluorescence decay studies by time-correlated single photon counting method showed that fluorescence decay kinetics of Thioflavin T in glycerol can be used for temperature measurements in the range 260–290 K. For 6-Me-BTA-2C molecule the range of the maximal sensitivity was shifted to higher temperatures (280–320 K). The obtained results about fluorescent properties and decay kinetics of Thioflavin T based dyes in highly viscous media can be used to develop nanoscale temperature sensors.

Collisional-radiative recombination of Ne-=SUP=-++-=/SUP=- and Ne-=SUP=-+-=/SUP=- ions with electrons in the decaying plasma of a low-pressure barrier discharge

The results of an experimental study and simulation of radiation generated by the processes of collisional-radiative recombination of neon ions Ne+ and Ne++ with electrons of the decaying plasma are presented. Plasma was created by a barrier discharge in a cylindrical glass tube with electrodes on its surface. Experimental conditions: neon pressure 0.65 Torr, electron density at the initial stage of the afterglow [e] ~ (1-5)·1011 cm-3. The main attention is paid to the comparative analysis of the collisional-radiative recombination of Ne+ and Ne++ ions based on the numerical solution of coupled differential equations for the densities of charged and long-lived excited particles and the electron temperature, taking into account the main elementary processes in decaying neon plasma. Comparison of the model solutions with the intensities of ionic and atomic spectral lines measured by the multichannel photon counting method indicates the need to refine the dependence of the rate of collisional-radiative recombination on the ion charge. Keywords: dielectric barrier discharge, doubly charged ions, collisional-radiative recombination, decaying plasma, elementary processes.

Ударно-радиационная рекомбинация ионов Ne-=SUP=-++-=/SUP=- и Ne-=SUP=-+-=/SUP=- c электронами в распадающейся плазме барьерного разряда низкого давления

The results of an experimental study and simulation of radiation generated by the processes of collisional-radiative recombination of neon ions Ne+ and Ne++ with electrons of the decaying plasma are presented. Plasma was created by a barrier discharge in a cylindrical glass tube with electrodes on its surface. Experimental conditions: neon pressure 0.65 Torr, electron density at the initial stage of the afterglow [e] ≈ (1 - 5) • 1011 cm-3. The main attention is paid to the comparative analysis of the collisional-radiative recombination of Ne+ and Ne++ ions based on the numerical solution of coupled differential equations for the densities of charged and long-lived excited particles and the electron temperature, taking into account the main elementary processes in decaying neon plasma. Comparison of the model solutions with the intensities of ionic and atomic spectral lines measured by the multichannel photon counting method indicates the need to refine the dependence of the rate of collisional-radiative recombination on the ion charge.

Investigation of a single-photon hybrid emitting system based on NV-centers in nanodiamonds integrated with GaP NWs

NV-centers can be used for quantum informatics, quantum communication and quantum sensing. The calculation of optical modes formed in a GaP cylindrical nanocavity covered by nanodiamonds has been performed. GaP nanowires have been synthesized with molecular beam epitaxy and played the role of optical resonators for light-emitting centers on the base of nanodiamonds with NV-centers. The optical characteristics of the GaP-based nanocavity were analyzed. The increase in the rate of spontaneous emission of NV-centers optically coupled to the nanocavity was estimated by the time correlated single photon counting method.

Nanosecond alpha-ray response and gamma-ray radiation resistance of a hydrothermal-grown bulk ZnO single crystal

We report the nanosecond alpha-ray response and gamma-ray radiation resistance of a hydrothermal-grown bulk zinc oxide (ZnO) single crystal. For its initial screening as a scintillator material of a fusion reactor’s radiation detector, the ZnO crystal was irradiated with gamma rays from a cobalt-60 (60Co) source resulting in an absorbed dose of 10 kGy. The crystal’s response under 5.5 MeV alpha-ray excitation from an americium-241 (241Am) source was then studied through photon-counting method. The gamma-ray-irradiated crystal exhibits a pulse height distribution and a 4.5 ns scintillation decay time similar to those of a non-irradiated crystal. Our results show that hydrothermal-grown bulk ZnO single crystals have a fast response under alpha-ray excitation and that gamma-ray irradiation has no apparent effect on the crystals’ scintillation properties.