Innovative airglow instrument based on constant photon count control

An experimental scheme and data processing approaches are proposed for measuring by analog photo detectors the normalized second-order correlation function of the biphoton field generated under spontaneous parametric down-conversion. Obtained results are especially important for quantum SPDC-based technologies in the long-wave spectral ranges, where it is difficult to use the single-photon detector at least in one of the two biphoton channels. The methods of discrimination of analog detection samples are developed to eliminate the negative influence of the detection noises and get quantitatively true values of both the correlation function and the detector quantum efficiency. The methods are demonstrated depending on whether two single-photon avalanche photo detectors are used in both SPDC channels, or at least one single-photon detector is replaced by a photo-multiplier tube which cannot operate in the photon counting mode.

A portable and sensitive time-resolved biosensor for capturing very low intensity light emission is a promising avenue to study plant delayed fluorescence. These weak emissions provide insight on plant health and can be useful in plant science as well as in the development of accurate feedback indicators for plant growth and yield in applications of agricultural crop cultivation. A field-based delayed fluorescence device is also desirable to enable monitoring of plant stress response to climate change. Among basic techniques for the detection of rapidly fluctuating low intensity light is photon counting. Despite its vast utility, photon counting techniques often relying on photomultiplier tube (PMT) technology, having restricted use in agricultural and environment measurements of plant stress outside of the laboratory setting, mainly due to the prohibitive cost of the equipment, high voltage nature, and the complexity of its operation. However, recent development of the new generation solid-state silicon photomultiplier (SiPM) single photon avalanche diode array has enabled the availability of high quantum efficiency, easy-to-operate, compact, photon counting systems which are not constrained to sophisticated laboratories, and are accessible owing to their low-cost. In this contribution, we have conceived, fabricated and validated a novel SiPM-based photon counting device with integrated plug-and-play excitation LED, all housed inside a miniaturized sample chamber to record weak delayed fluorescence lifetime response from plant leaves subjected to varying temperature condition and drought stress. Findings from our device show that delayed fluorescence reports on the inactivation to the plant’s photosystem II function in response to unfavorable acute environmental heat and cold shock stress as well as chronic water deprivation. Results from our proof-of-concept miniaturized prototype demonstrate a new, simple and effective photon counting instrument is achieved, one which can be deployed in-field to rapidly and minimally invasively assess plant physiological growth and health based on rapid, ultra-weak delayed fluorescence measurements directly from a plant leaf.

To realize novel photon-counting energy-dispersive X-ray computed tomography (CT), we have developed a low-dose CT scanner using a detector consisting of a cerium-doped yttrium aluminum perovskite [YAP(Ce)] crystal and a small photomultiplier tube (PMT). X-ray photons are absorbed by the YAP(Ce) crystal, and negative outputs are produced from the PMT. The PMT outputs are amplified by an inverse voltage-to-voltage amplifier, and the event pulses are counted by the counter with a low threshold energy of 20 keV. First, almost all the photons are counted without the photon-energy dependence, since the scintillation-photon number produced by one X-ray photon is proportional to the photon energy. Second, the energy-dispersive imaging is performed using the self-beam hardening by the object. The maximum photon count of the projection data is determined after the air absorption, and the effective photon energy increases with increasing digital-amplification factor at the constant maximum count. In the triple-energy CT, the X-ray beam diameter was 0.5 mm, and the spatial resolutions were approximately 0.3×0.3 mm2 . The exposure time for DE-CT was 9.8 min at a total rotation angle of 180°.

In any quantum communication system, such as a quantum key distribution (QKD) system, data rates are mainly limited by the system clock rate and the various link losses. While the transmission clock rate is limited by the temporal resolution of the single-photon detectors, losses in a fiber-based quantum communication system can be minimized by operating in the near infrared range (NIR), at 1310 nm or 1550 nm. Commercially available InGaAs-based avalanche photo-diodes (APDs) can be operated as single-photon detectors in this wavelength range [Hadfield, 2009]. Due to the severe after-pulsing, InGaAs APDs are typically used in a gated mode and this can limit their application in high-speed quantum communications systems. Superconducting single-photon detectors (SSPDs) can work in the NIR wavelength range with good performance [Gol’tsman et al. 2001; Hadfield, 2009]. However, SSPDs require cryogenic temperatures, and are not widely available on the commercial market at present. In addition, InGaAs/InP based photomultiplier tubes (PMT) can operate in the NIR range, but its performance is limited by very low detection efficiency (1 % at 1600 nm) and large timing jitter (1.5 ns) [Hamamatsu, 2005]. Microchannel plates (MCP) are micro-capillary electron multipliers coated with an electron-emissive material and multiply photon-excited electrons from a photon cathode [Wiza, 1979]. MCPs usually have faster rise times and lower timing jitter than is achievable with PMTs. InGaAs MCPs can work in the NIR range. These MCPs, but are limited by low detection efficiency (~1 %) [Martin, J. & Hink P. 2003]. On the other hand, silicon based avalanche photo-diodes (Si APDs) are compact, relatively inexpensive, and can be operated at ambient temperatures with high detection efficiency and low noise in the visible or near-visible range. Unfortunately they do not work at wavelengths longer than 1000 nm. For those wavelengths, an up-conversion technique has been developed that uses sum-frequency generation (SFG) in a non-linear optical medium to convert the signal photons to a higher frequency (shorter wavelength) in the visible or near visible range. The up-converted photons can then be detected by a Si APD. Up-conversion detectors use commercially available components and devices, and are a practical solution for many applications in quantum communications. To date, several groups have successfully developed highly efficient up-conversion single-photon detectors in the nearinfrared range using periodically poled lithium niobate (PPLN) waveguides [Diamanti et al., 2005; Langrock et al., 2005; Thew et al., 2006; Tanzilli et al., 2005; Xu et al., 2007;] and bulk crystals [Vandevender & Kwiat, 2004].

During the past two decades there has been a dramatic rise in the use of functional near-infrared spectroscopy (fNIRS) as a neuroimaging technique in cognitive neuroscience research. Diffuse optical tomography (DOT) and optical topography (OT) can be employed as the optical imaging techniques for brain activity investigation. However, most current imagers with analogue detection are limited by sensitivity and dynamic range. Although photon-counting detection can significantly improve detection sensitivity, the intrinsic nature of sequential excitations reduces temporal resolution. To improve temporal resolution, sensitivity and dynamic range, we develop a multi-channel continuous-wave (CW) system for brain functional imaging based on a novel lock-in photon-counting technique. The system consists of 60 Light-emitting device (LED) sources at three wavelengths of 660nm, 780nm and 830nm, which are modulated by current-stabilized square-wave signals at different frequencies, and 12 photomultiplier tubes (PMT) based on lock-in photon-counting technique. This design combines the ultra-high sensitivity of the photon-counting technique with the parallelism of the digital lock-in technique. We can therefore acquire the diffused light intensity for all the source-detector pairs (SD-pairs) in parallel. The performance assessments of the system are conducted using phantom experiments, and demonstrate its excellent measurement linearity, negligible inter-channel crosstalk, strong noise robustness and high temporal resolution.

The time correlated single photon (TCSP) technique is more commonly known as the “single photon counting” method, a term that has led to confusion with conventional photon counting detection. Both are spectroscopic detection methods but they differ greatly in principle, instrumentation, and application. Perhaps the distinction between the two techniques will be served by first briefly describing photon counting. Photon counting is an instrumental technique for measuring low levels of light or particle beam densities (1–5). Individual photons incident on a photomultiplier tube (PMT) create discrete pulses or bursts of electrons arriving at the anode at a rate directly proportional to the photon flux. The instrumentation is relatively straightforward. The current pulse from the PMT anode is converted to a voltage, amplified, and sent to a pulse height discriminator. Only those pulses within preset voltage limits are passed on to a counter. Advantages of photon counting include: 1) the signal-to-noise (S/N) ratio is enhanced compared to the DC current measurement method, 2) the data are in digital form, 3) the sensitivity is greater at low light levels, 4) the measurements may be integrated over long periods of time resulting in higher precision and accuracy(2).

The Differential Absorption Lidar (DIAL) technique is one of the most effective methods for detecting atmospheric gases. It is based on the interaction between laser-emitted light and atmospheric molecules. The backscattered optical signal is converted into an electrical signal using photomultiplier tubes or other types of detectors. Two main detection approaches are commonly used: analog detection and photon-counting detection. While the analog mode is widely employed, it suffers from limited sensitivity. The photon-counting mode, although more suitable for detecting extremely weak signals, faces challenges in daytime measurements due to strong solar background noise. The main objective of this study is to evaluate the performance of the photon-counting technique to enable the DIAL system to detect extremely weak optical signals. To this end, modeling and simulation of the parameters influencing system performance have been carried out. Furthermore, the impact of using ultra-narrow band filter (UNBF) has been investigated and compared to that of conventional interference filter, with the aim of reducing background noise in daytime measurements and improving the transmission of the useful signal. The results show that the photon counting acquisition technique for a DIAL system or P-DIAL (Photon-counting DIAL) provides superior performance in terms of signal quality and measurement accuracy compared to analogue detection using an UNBF for noise limitation.

The optically coupled current mirror (OCCM) is a novel optoelectronic architecture that replicates at ground potential a current flowing in an isolated conductor. The mirroring action is done without need to bring any power to the potential of the conductor where the current flows, as its input stage is completely passive. This feature is particularly important when the conductor is at high voltage (HV), a typical case being the photomultiplier tubes (PMTs) biased with positive HV, or when the number of channels is very large as it is the case of many particle physics experiments. The OCCM has been used to equip the two prototype telescopes, each one comprising 440 PMTs, of the ultra-high-energy cosmic-ray experiment Pierre Auger. Despite that the PMT's anodes were at HV, the DC or slowly varying component of the anode current was measured with high resolution, clearly revealing the presence of faint stars, planets, and other similar objects which determine the sky background light. In this paper we describe the principle of operation of the OCCM and its application to the measurement of the anode current of PMTs biased with cathode grounded, as well as the first results obtained with the OCCM on linear transmission of 2-/spl mu/s-width pulses, via fiber optics.

Most of the dust monitors are based on optical principle: the scattered light intensity is registered. The classical approach is using the multiple photon optical signal intensity and processing. Single photon detection -- photon counting is exploited in Satellite Laser Ranging and was implemented in space born application for Mars Surveyor Program 98, as well. The main advantage of single photon detection is an extreme sensitivity, the entire digital approach, no analog signal is treated. All the light intensity information is acquired on the basis of statistical data treatment. The dust detector consists of the LED diode based transmitter, single photon solid state diode detector and the digital data processing unit. The light beam from the LED diode passing the dust column is detected in a photo detector. The detector employs the avalanche Silicon photodiode 40 micrometers diameter active area and is operated in a passive gating and active quenching mode above its breakdown voltage. The detector provides uniform digital pulses, one for each photon detected. The light intensity measurement is converted into the photon flux counting -- frequency or event counting. The microcomputer controlled data processing electronics counts the detector output pulses, accounts for detector dark count rate, calibration constants, and computes the corresponding dust concentration averaged over desired period. The second LED located close to the detector is used as a reference light source to eliminate the temperature, aging and sensor contamination influence. The laboratory measurements show the long term and temperature stability of the scale within 1%. The setup was tested at the cement plant smoke stack and compared to the commercial optical dust concentration monitor operating on analog multiphoton principle. Due to an extreme optical sensitivity of the photon counting detector, the energy balance is favorable to realize lightweight equipment by a factor of ten in comparison to analogue-based device. The photon counting principle along with the self-calibration setup does not require re-calibration. The optical apertures involved are of the order of millimeters what reduces the problems of contamination of the device by the dust monitored. As no collimating optics is used, the no optical alignment is required.

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.

In order to detect a weak signal light that appears after an intensive pulsed background light, we constructed a light detection module that consisted of an internally-gated photomultiplier tube (PMT) and a phase sensitive detector (PSD). Plural even-numbered dynodes of a miniature PMT were controlled for the internal gate operation and the output signal from the PMT was fed into the PSD integration circuit (IC) that worked synchronously with the gated PMT. The module acts as a sort of lock-in light detection system. The combination of the gate-on PMT and the PSD IC detects the weak signal light while the gate-off PMT rejects the intensive pulsed background light. From fundamental performance tests, we found that a background rejection ratio (BGRR) of the gated PMT up to 10,000 could be obtained. We carried out an evaluation experiment using a multi-white light-emitting diode (LED) to demonstrate the pulsed-background-light rejection capability of the module.

For the measurement of astronomical gamma ray radiation in the energy range 50 keV to several MeV usually photomultiplier tubes (PMT) with scintillation crystals are used. However, due to the internal detection mechanism high voltage and single photon counting are required leading to heavy and structurally unpractical systems. Even APD's (avalanche photodiodes) do not circumvent the problem of the high voltage. Recent improvements in the performance of semiconductor detectors allow the use of large area and low noise pin photodiodes as innovative scintillation detectors with 40 - 100 V operating voltage only. Tl-doped CsI as scintillation crystal with a superior light yield has not only a much higher photon output compared to the light yield of pure CsI and BGO crystals which are used for the gamma ray detection with PMTs, but has also a perfect matching of spectral properties of the photodiode. This paper presents a comprehensive comparison with conventional PMT scintillation detector systems and the development activities of full size breadboards with such a photodiode/CsI(Tl) detector set-up. The relevant functional performance test results have shown the high technical maturity of this detector system and the principal feasibility for the application either in the INTEGRAL spectrometer and imager anticoincidence shield (ACS) or in image central detector system. The dedicated ACS configuration design featuring optimized mass budget combined with high gamma ray stopping efficiency is figured.

The neutrino-less double beta decay (0νββ) is a powerful tool to probe the neutrino mass. The 0νββ is forbidden in Standard Model (SM) due to the violation of lepton number conservation. In experiments searching for 0νββ, the two-neutrino double beta decay (2νββ), which is an allowed process in SM, behaves as an irreducible background within the energy of interest. To discriminate the 0νββ from 2νββ, the energy resolution must be improved. The CANDLES experiment is searching for the 0νββ of <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">48</sup> Ca using CaF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (pure) scintillator as the detector and the source. Scintillation photons are collected by Photo Multiplier Tubes (PMTs) surrounding the crystals. A Flash Analog-to-Digital Converter records the waveform of each PMT. Because of the long decay time of CaF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (1 μsec), we make a signal integral of 4 μsec to calculate the obtained energy. Thus, the other fluctuation in the baseline is accumulated in the signal integration, and it makes the energy resolution worse. To reduce this fluctuation, we can count the number of photoelectrons in every PMT. Still, we have a significant overlapping probability of single photoelectron signals. This overlapping probability implies the photoelectrons lost, which causes terrible energy resolution. To improve the energy resolution, we introduce an alternative method named "partial photon counting" by dividing the waveform into two parts, then, perform signal integral in the prompt part and photon counting the second part. As a result, the energy resolution is reduced 4.0-3.5 % at 1460 keV (γ-ray of <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">40</sup> K) and 3-2.7 % at 2615 keV (γ-ray of <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">208</sup> Tl).

Novel micropixel avalanche photodiodes (MAPD) with super high pixel density

The III-Nitride material system is rapidly maturing; having proved itself as a material for LEDs and laser, and now finding use in the area of UV photodetectors. However, many UV applications are still dominated by the use of photomultiplier tubes (PMT). PMTs are capable of obtaining very high sensitivity using internal electron multiplication gain (typically ~10 6 ). It is highly desirable to develop a compact semiconductor-based photodetector capable of realizing this level of sensitivity. In principle, this can be obtained in III-Nitrides by taking advantage of avalanche multiplication under high electric fields – typically 2.7 MV/cm, which with proper design can correspond to an external reverse bias of less than 100 volts. In this talk, we review the current state-of-the-art in III-Nitride solar- and visible-blind APDs, and present our latest results on GaN APDs grown on both conventional sapphire and low dislocation density free-standing c- and m-plane GaN substrates. Leakage current, gain, and single photon detection efficiency (SPDE) of these APDs were compared. The spectral response and Geiger-mode photon counting performance of UV APDs are studied under low photon fluxes, with single photon detection capabilities as much as 30% being demonstrated in smaller devices. Geiger-mode operation conditions are optimized for enhanced SPDE.