This PDF file contains the front matter associated with SPIE Proceedings Volume 6771, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

Time-correlated single photon counting (TCSPC) is based on the detection of single photons of a periodic light signal, measurement of the detection time of the photons, and the build-up of the photon distribution versus the time in the signal period. TCSPC achieves a near ideal counting efficiency and transit-time-spread-limited time resolution for a given detector. We present an advanced TCSPC technique featuring multi-dimensional photon acquisition and a count rate close to the capability of currently available detectors. The technique is able to acquire photon distributions versus wavelength, spatial coordinates, and the time on the ps scale, and to record fast changes in the fluorescence lifetime and fluorescence intensity of a sample. Biomedical applications of advanced TCSPC techniques include time-domain optical tomography, recording of transient phenomena in biological systems, spectrally resolved fluorescence lifetime imaging, FRET experiments in living cells, and the investigation of dye-protein complexes by fluorescence correlation spectroscopy. We demonstrate the potential of the technique for selected applications.

Obtaining geometric snapshots of a protein as it folds will yield insights into how proteins achieve their unique functional native 3-dimensional structure. Time-resolved FRET and time-resolved anisotropy are valuable tools toward obtaining information about site-specific distances and side-chain mobility of the transient structures formed within microseconds of initiating protein folding. To access this timescale we have merged dual-channel TCSPC detection with recently developed laser-micromachining based microsecond turbulent mixer technology to obtain site-specific distance information and rotational correlation times of protein folding intermediates in the 30 microsecond to seconds timescale. Application of this approach shows that chain collapse to globular structures can occur in the several microsecond timescale even for large proteins.

Rejection of transplanted hearts remains an important reason for death of transplanted children. Finding diagnostic tools for its detection can therefore improve the prognosis in this population of patients. Endomyocardial biopsy (EMB) by cardiac catheterization is currently accepted as the "gold standard" for the diagnosis of rejection. Here, we investigate new approach to monitor mitochondrial metabolic state of cardiac cells using spectrally-resolved autofluorescence lifetime detection of nicotinamide adenine dinucleotide (phosphate), or NAD(P)H, the principal electron donor in mitochondrial oxidative energy metabolism responsible for vital ATP supply of cardiomyocytes. NAD(P)H autofluorescence is long used for non-invasive fluorescent probing the metabolic state of the heart. In this contribution we report dynamic characteristics of NAD(P)H fluorescence decays in living human cardiomyocytes from EMB, following excitation by UV-pulsed laser diode and detection by spectrally-resolved time-correlated single photon counting. At least a 3-exponential decay model, with 0.5-0.7 ns, 1.9-2.4 ns and 9.0-15.0 ns lifetimes, is necessary to describe cardiomyocyte autofluorescence in human cells. When gathered data were compared to those recorded under same conditions in rats, autofluorescence in human hearts was found significantly lower in comparison to rat ones. Rotenone, the inhibitor of the Complex I of the respiratory chain, increased the fluorescence in human cardiac cells, making them more comparable to experimental rat model. These results suggest that human cardiac cells are more metabolically active than the rat ones in the same conditions. Presented work proposes a new tool for evaluation of oxidative metabolism changes in transplanted hearts.

We present a new approach for analysis of multi-wavelength time-resolved spectroscopy data, based on sequential spectral unmixing. Principal component analysis was used to identify the number and spectral profiles of the main components of intrinsic flavin signal in multi-wavelength time-resolved fluorescence recordings from isolated living cardiac myocytes. To determine these components, natural variations in the cardiomyocyte autofluorescence spectra were induced by modulators of mitochondrial metabolism and respiration. Using aforementioned approach we have identified two main components of intrinsic flavin emission in cardiac myocytes. The first component show emission maximum at 486-504 nm and mean lifetime of 1.2 nanoseconds, the second component with peak at 522 nm has two-exponential decay with fluorescence lifetimes of 0.3 and 3.1 nanoseconds. Comparison of gathered new results to our previous studies of flavins in vitro and in cardiac cells clearly points to the fact that the estimated spectral components correspond to flavin adenine dinucleotide (FAD) bound to enzyme(s) of mitochondrial metabolic chain, and to free FAD, respectively.

Fluorescence imaging techniques are powerful tools in the biological and biomedical sciences, because they are minimally invasive and can be applied to live cells and tissues. The fluorescence emission can be characterized not only by its intensity and position, by also by its fluorescence lifetime, polarization and wavelength. Fluorescence Lifetime Imaging (FLIM) in particular has emerged as a key technique to image the environment and interaction of specific proteins in living cells. Using a time-correlated single photon counting (TCSPC)-based FLIM set-up, we find that the fluorescence lifetime of GFP-tagged proteins in cells is a function of the refractive index of the medium the cells are suspended in. In addition, combining Fluorescence Recovery After Photobleaching (FRAP) of fluorescently labeled proteins of different sizes in sol gels with time-resolved fluorescence anisotropy measurements, we demonstrate that we can measure their lateral and rotational diffusion. This allows us to infer the size and connectivity of the pores in the sol gel matrix. Moreover, wide-field photon counting imaging, originally developed for astronomical applications, is a powerful imaging method because of its high sensitivity and excellent signal-to-noise ratio. It has a distinct advantage over CCD-based imaging due to the ability to time the arrival of individual photons. The potential of time-resolved wide-field photon counting imaging with a fast CMOS camera applied to luminescence microscopy is demonstrated.

We herein describe a time-of-flight (TOF) technique to localize in 3D the position of a small fluorophore-filled inclusion immersed in a scattering medium. To achieve this, we exploit the arrival time of early excited and fluoresced photons. This is an embodiment of fluorescence diffuse optical tomography (FDOT) which aims to find the position of fluorescent heterogeneities in 3D in thick turbid media non-invasively via optical imaging techniques. In Ref. 4, we gave a short review of previous work on the problem of localizing a fluorescent inclusion via time-resolved measurements. This will not be discussed again here.

First pathological alterations occur at cellular level, most in metabolism. An indirect estimation of metabolic activity in cells is measurement of microcirculation. Measurements of tissue autofluorescence are potentially suited for direct investigation of cellular metabolism. Besides redox pairs of co-enzymes (NADH-NAD, FADH2-FAD) several other fluorophores are excited in tissue. In addition, a number of anatomical structures are simultaneously excited, when investigating the eye-ground. In this study, spectral and time resolved comparison was performed between purified substances, single ocular structures and in vivo measurements of the time-resolved autofluorescence at the human eye. In human eyes, the ageing pigment lipofuscin covers other fluorophores at the fundus in long - wave visible range. Applying lifetime measurements, weakly emitting fluorophores can be detected, when the lifetimes are different from the strongly emitting fluorophore. For this, the autofluorescence was excited at 468 nm and detected in two spectral ranges (500 nm-560 nm, 560 nm-700 nm). In tri-exponential fitting, the short lifetime corresponds to retinal pigment epithelium, the mean lifetime corresponds probably to neural retina and the long lifetime is caused by fluorescence of connective tissue.

The acquisition time of TCSPC FLIM depends on the number of pixels of the image, on the required lifetime accuracy, and on the count rate available from the sample. For samples with high fluorophore concentrations, such as stained tissue or plant cells the available count rates may come close to the maximum counting capability of the currently used TCSPC FLIM techniques. We describe the behaviour of TCSPC at high count rates and estimate the size of counting loss and pile-up effects. It turns out that systematic lifetime errors are smaller than previously believed. TCSPC FLIM can therefore be used to record fast sequences of fluorescence lifetime images. Fast sequential FLIM will be demonstrated for the measurement of chlorophyll transients in living plant tissue.

We demonstrate a two-photon absorption scanning microscope capable of imaging two focal planes simultaneously. The 23MHz fundamental laser is split in two, one part delayed in time while the other is focused with a deformable mirror to change its divergence. Both parts are then recombined to form a 46MHz pulse train consisting of two interlaced trains with different divergences that after the objective are focused at different sample depths. At the detection path, photon counting techniques allow photons coming from each depth to be separated based on their relative timing with respect to the 46MHz train. The separation is accomplished using a field-programmable gate array that has been programmed to switch back and forth between two counters at a rate provided by a master clock generated by the 46MHz pulse train. The computer that controls the scanners reads and resets the counters before moving to a new pixel. The scheme is demonstrated for two depths but can be extended to a larger number, the ultimate limit being the fluorescence lifetime. This technique could also be implemented for second or third harmonic generation microscopy, in this case the ultimate achievable number of focal planes would be determined by the electronics speed.

Confocal time resolved single-molecule spectroscopy using pulsed laser excitation and synchronized multi channel time correlated single photon counting (TCSPC) provides detailed information about the conformational changes of a biological motor in real time. We studied the formation of adenosine triphosphate, ATP, from ADP and phosphate by F_oF₁-ATP synthase. The reaction is performed by a stepwise internal rotation of subunits of the lipid membrane-embedded enzyme. Using Förster-type fluorescence resonance energy transfer, FRET, we detected rotation of this biological motor by sequential changes of intramolecular distances within a single F_oF₁-ATP synthase. Prolonged observation times of single enzymes were achieved by functional immobilization to the glass surface. The stepwise rotary subunit movements were identified by Hidden Markov Models (HMM) which were trained with single-molecule FRET trajectories. To improve the accuracy of the HMM analysis we included the single-molecule fluorescence lifetime of the FRET donor and used alternating laser excitation to co-localize the FRET acceptor independently within a photon burst. The HMM analysis yielded the orientations and dwell times of rotary subunits during stepwise rotation. In addition, the action mode of bactericidal drugs, i.e. inhibitors of F_oF₁-ATP synthase like aurovertin, could be investigated by the time resolved single-molecule FRET approach.

We demonstrate the feasibility of time-resolved diffuse reflectance at small source-detector separations using a single-photon avalanche photodiode (SPAD) operated in time-gated mode. Photon time distributions at an interfiber distance of 0.2 cm were obtained on tissue phantoms with a reduced scattering coefficient of 10 cm^-1, and an absorption coefficient of 0.1 cm^-1, with a dynamic range of 10⁶ and collecting photons at arrival times up to 4 ns. By time-gating the initial photons, carrying information mainly from superficial layers, it is possible to detect longer lived photons that have explored deeper depths even at almost null interfiber distances. The proposed approach should provide higher number of photons at any arrival time, higher contrast, and better spatial resolution as compared to longer interfiber distances.

The first successful photon-counting airborne laser altimeter was demonstrated in 2001 under NASA's Instrument Incubator Program (IIP). This "micro-altimeter" flew at altitudes up to 22,000 ft (6.7 km) and, using single photon returns in daylight, successfully recorded high resolution images of the underlying topography including soil, low-lying vegetation, tree canopies, water surfaces, man-made structures, ocean waves, and moving vehicles. The lidar, which operated at a wavelength of 532 nm near the peak of the solar irradiance curve, was also able to see the underlying terrain through trees and thick atmospheric haze and performed shallow water bathymetry to depths of a few meters over the Atlantic Ocean and Assawoman Bay off the Virginia coast. Sigma Space Corporation has recently developed second generation systems suitable for use in a small aircraft or mini UAV. A frequency-doubled Nd:YAG microchip laser generates few microjoule, subnanosecond pulses at fire rates up to 22 kHz. A Diffractive Optical Element (DOE) breaks the transmit beam into a 10x10 array of quasi-uniform spots which are imaged by the receive optics onto individual anodes of a high efficiency 10x10 GaAsP segmented anode microchannel plate photomultiplier. Each anode is input to one channel of a 100 channel, multistop timer demonstrated to have a 100 picosecond timing (1.5 cm range) resolution and an event recovery time less than 2 nsec. The pattern and frequency of a dual wedge optical scanner, synchronized to the laser fire rate, are tailored to provide contiguous coverage of a ground scene in a single overflight.

We have characterized the performance of photon counting pseudorandom noise (PN) code laser ranging system at both 1064 and 1570 nm. The PN code modulation is a binary signal which is widely used in telecommunications and RF ranging applications. When used in lidar PN code modulation allows the transmitter to operate with a peak power, equal to only twice the average power which is compatible with the optical fiber communication technology. Our photon counting receiver approach accumulates the received photon stream into a histogram, then cross correlates the histogram with the original PN code sequence. The time of flight is given by the location of the peak in the correlation function. For multiple targets within the laser beam footprint, each target produce a peak in the correlation function at the delay corresponding to the target range. Our approach for altimetry also uses receiver range bin much shorter than the PN code bit period. This permits the correlation to be calculated with higher time resolution than the PN code bit period and substantially improves the time and range resolution. Our laboratory measurements with a breadboard receiver shows a greater than 90% probability of detection in a 0.5 msec integration time with 50 fW average received optical power at 1064 nm when using an InGaAsP hybrid photomultiplier tube detector. We have also achieved a less than 5cm rms ranging precision, when using a 250 psec range bin and at about 100 KHz detected signal photon rate.

Single-Photon Avalanche Diodes (SPADs) for near-infrared (800-1700 nm) wavelengths can be manufactured both in InGaAs/InP and in germanium. Recently, new InGaAs/InP SPADs became commercially available with good overall performances, but with the intrinsic bottleneck of strong afterpulsing effect, originated in the InP multiplication layer. At present, germanium technology is not exploited for single-photon detectors, but previous devices demonstrate lower afterpulsing even at very low temperatures and promising dark count rate when employing pure manufacturing process. In this work, we compare germanium and InGaAs/InP SPADs in terms of dark counts, afterpulsing, timing jitter, and quantum efficiency. Eventually, we highlight the motivations for considering germanium as a key material for single-photon counting in the NIR.

In the past, it has been necessary to operate avalanche photodiodes (APDs) in Geiger mode to perform photon counting. The gain and noise performance of available linear-mode APDs was too poor to detect the photocurrent pulse from a single photon using existing amplifier technology. We review the performance thresholds required to achieve linear-mode photon counting, and present measurements from two APD designs that meet the gain and noise requirements. The first design is a previously-reported vertical-junction, electron-avalanche HgCdTe device fabricated from 4.06-μm-cutoff liquid phase epitaxy (LPE)-grown material. These HgCdTe APDs have an excess noise factor of approximately F~1 at a gain of M=150 when measured at 196 K. The second design is a novel InAlAs/InGaAs structure grown by molecular beam epitaxy (MBE) entirely from alloys lattice-matched to InP. The maximum gain found for this new design was as high as M=2000 at 235 K, but the principle of its operation limits the best noise performance of the prototype to gains below M=20, for which it has an excess noise factor of F~2.3 at room temperature (corresponding to k~0.02 when fit to McIntyre's model). This design can be scaled to deliver the same noise performance at higher gains.

We report high gain, high sensitivity 1064-1550 nm avalanche photodiodes (APDs) that are capable of single photon counting in the linear mode below the breakdown voltage and at room temperature. Epitaxial Technologies has developed AlInAs/GaInAs APDs with multiplication gains as high as 347,000, sensitivities of -69 to -77 dBm and photon detection efficiencies as high as 27%. The single photon counting APDs are free of afterpulse artifacts even for pulse widths in the nanosecond range. They can detect single photons at up to 139 MHz and have the capability for gigahertz repetition rate. Based on innovative and proprietary APD production technologies, the APDs have excess noise factors as low as 2 with the high gain. To our knowledge, these are the highest multiplication gains simultaneous with low excess noise factors and high sensitivities reported so far for long wavelength APDs.

Single photon detectors are key components for a wide range of applications in the near infrared (NIR) wavelength range between 1.0 and 1.7 μm. To achieve high performance single photon detection in the NIR wavelength range, single photon avalanche diodes (SPADs) based on the InGaAsP quarternary material system lattice-matched to InP are likely to provide the most appropriate solution in numerous situations. In this paper, we describe the design, characterization, and modeling of InGaAsP/InP avalanche diodes designed for single photon detection at wavelengths of 1.55 μm and 1.06 μm. Critical performance parameters of these SPADs, including dark count rate, photon detection efficiency, and afterpulsing have been studied both experimentally and theoretically. The models developed for the simulation of device performance provided good agreement with experimental results. The relationship between dark count rate and photon detection efficiency is investigated for 1.55 μm SPADs under gated mode operation and 1.06 μm SPADs under both gated mode and free-running operations. We also describe in detail the dependence of afterpulsing effects on numerous operating conditions.

We have developed single photon counting image intensifier tubes combining position and time information read-out with at least 500x500 pixels and sub-nanosecond time resolution. This image intensifier type uses a resistive screen instead of a phosphor screen and the image charge pickup anode is placed outside the sealed tube. We present a novel delay-line anode design which allows for instance detecting simultaneously arriving pairs of photons. Due to the very low background this technique is suited for applications with very low light intensity and especially if a precise time tagging for each photon is required. We show results obtained with several anode types on a 25 mm image intensifier tube and a 40 mm open-face MCP detector and discuss the performance in neutron radiography, e.g. for homeland security, and the prospects for applications like Fluorescence Life-time Imaging Microscopy (FLIM), astronomy and X-ray polarimetry.

We present a novel time-resolved photon counting imaging technique and its use in multi-dimensional luminescence spectroscopy. By using an ultrafast camera coupled to an image intensifier on a microscope, we demonstrate the potential of wide-field time-correlated single photon counting, with a count rate of up to 5 Mhz. This system has the advantage of allowing the detection of single photons in parallel in every pixel. We measured the luminescence decay of Europium Polyoxometalate (POM), and observed contrast on lifetime images of Eu-POM on silver nanocrystals.

We demonstrate photon-number discrimination using a novel semiconductor detector that utilizes a layer of self-assembled InGaAs quantum dots (QDs) as an optically addressable floating gate in a GaAs/AlGaAs δ-doped field-effect transistor. When the QDOGFET (quantum dot, optically gated, field-effect transistor) is illuminated, the internal gate field directs the holes generated in the dedicated absorption layer of the structure to the QDs, where they are trapped. The positively charged holes are confined to the dots and screen the internal gate field, causing a persistent change in the channel current that is proportional to the total number of holes trapped in the QD ensemble. We use highly attenuated laser pulses to characterize the response of the QDOGFET cooled to 4 K. We demonstrate that different photon-number states produce well resolved changes in the channel current, where the responses of the detector reflect the Poisson statistics of the laser light. For a mean photon number of 1.1, we show that decision regions can be defined such that the QDOGFET determines the number (0, 1, 2, or ≥3) of detected photons with a probability of accuracy ≥83 % in a single-shot measurement.

A measurement system is described for acquiring the gain distributions of avalanche photodiodes (APDs) in a range of low average gain. The system is based on an ultralow-noise capacitive transimpedance amplifier to readout the charges generated in an APD. The low noise level of the readout circuit about 7 electrons at the sampling rate of 200 Hz enables us to characterize the gain distributions. The gain distribution of a commercial silicon (Si) APD measured at gain of 3.29 using this system is presented.

We discuss the difficulties of photon-counting at extremely high rates and introduce a scheme for a photon-counting detection system that addresses these difficulties. The method uses an array of N detectors and a 1-by-N optical switch with a control circuit to direct input light to live detectors. We compare performance of our system to other, passive detection systems and show that our detection system can handle incident photon rates higher than otherwise possible by suppressing the effects of detector deadtime. To support this claim, we present results of theoretical analysis and a proof-of- concept experiment. In particular, both calculations and the experiment prove that a group of intelligently managed N detectors provides an improvement in operation rate that can exceed the improvement that would be obtained by either a single detector with deadtime reduced by 1/N, even if it were feasible to produce a single detector with such a large improvement in deadtime, or a passive beamsplitter tree system with N detectors. In addition to deadtime reduction, our scheme reduces afterpulsing as well as background counts (such as dark counts). We conclude that an intelligent active management of a group of N detectors is the best arrangement of photon-counting detectors to handle high photon rates, an important technological challenge for fast developing quantum metrology and quantum key distribution applications.

One of the main drawbacks of Single Photon Avalanche Diode arrays is the optical crosstalk between adjacent detectors. This phenomenon represents a fundamental limit to the density of arrays, since the crosstalk increases with reducing the distance between adjacent devices. In the past, crosstalk was mainly ascribed to the light propagating from one detector to another through a direct optical path. Accordingly, deep trenches coated with metal were introduced as optical isolation barriers between pixels. This solution, however, was unable to completely prevent the crosstalk. In this paper we present experimental evidence that a significant contribution to crosstalk comes from photons reflected internally at the bottom of the chip. These photons can bypass trenches making them ineffective. We also propose an optical model suitable to predict the dependence of crosstalk on the position within the array.

Photon-counting combined with M-ary PPM is practically the most efficient means for implementing freespace optical communications. Data rates are limited by the speed of the counting devices. We calculate here the performance with soft decision coding that one can expect for speeds so fast that device-limiting timing jitter is the primary source of measurement error.

We present a multichannel photon counting module that exploits a monolithic array of single-photon avalanche diodes (SPADs). The detector array consists of eight 50μm diameter SPADs featuring low dark counting rate and high photon detection efficiency (50% at 550nm); inter-pixel crosstalk probability is as low as 2•10^-3. The use of highly integrated active quenching circuits makes it possible to design a very compact read-out circuit, yet providing eight fully independent counting channels and gating capability. The detection module maintains the same physical dimensions of commercially available single element modules and can be used as a plug-in replacement to add multichannel capabilities to existing measurement setups. Full characterization of module performance is here presented.

A 4H-SiC SPAD with an off-mesa bonding pad operating at 280nm is presented in this paper, with a low dark count rate of 14kHz and 27kHz at single photon detection efficiency of 3.3% and 4.5%, respectively. The device has a low breakdown voltage of 117V and a low dark current of 17fA, 49fA and 147fA at 50%, 90%, and 95% of breakdown voltage, respectively. The quantum efficiency is measured to be 28% (32%) at 280nm (270nm) with a UV to visible rejection ratio >1400 (>1600).

The article describes a principle of 3D-positioning by pseudo-ranges using ultrashort laser pulses. It can be used as an local optical positioning system (LOPS). Laser pulses are sent out highly divergent to four detectors with known positions. The goal is to determine the 3D position of the laser pulser. A TSCPC system is used to measure differential time of flight between the four detectors. The main problem of differential TCSPC is the small probability to detect each two photons of the same pulse at different positions. It therefore takes the highest possible laser power to measure pseudo-ranges this way over a distance of 30 m and more. A second requirement for such a system is mobility. This is why we tried to realize the laser subystem with a diode laser and subsequent beam shaping using axicon optics. Investigations with different ps-laser pulsers and different detector types are shown. An important investigation concerning the ranging accuracy was the comparison of two TCSPC systems, one with TAC and ADC and the other with TDC. Furthermore the development of an elastic lens for variable defocussing of the laser is shown.

The absorption effect of the back surface boundary of a diffuse layer was studied via laser generated reflection speckle pattern. The spatial speckle intensity provided by a laser beam was measured. The speckle data were analyzed in terms of fractal dimension (computed by NIH ImageJ software via the box counting fractal method) and weak localization theory based on Mie scattering. Bar code imaging was modeled as binary absorption contrast and scanning resolution in millimeter range was achieved for diffusive layers up to thirty transport mean free path thick. Samples included alumina, porous glass and chicken tissue. Computer simulation was used to study the effect of speckle spatial distribution and observed fractal dimension differences were ascribed to variance controlled speckle sizes. Fractal dimension suppressions were observed in samples that had thickness dimensions around ten transport mean free path. Computer simulation suggested a maximum fractal dimension of about 2 and that subtracting information could lower fractal dimension. The fractal dimension was shown to be sensitive to sample thickness up to about fifteen transport mean free paths, and embedded objects which modified 20% or more of the effective thickness was shown to be detectable. The box counting fractal method was supplemented with the Higuchi data series fractal method and application to architectural distortion mammograms was demonstrated. The use of fractals in diffusive analysis would provide a simple language for a dialog between optics experts and mammography radiologists, facilitating the applications of laser diagnostics in tissues.

Time-resolved experiments employing the timing distribution of synchrotron radiation in contemporary electron storage rings demand a precise control of the bunch fill pattern. At BESSY an X-ray detector based on an Avalanche Photodiode Diode (APD) in combination with time-correlated single photon counting (TSPC) has been developed and used since 1999. After improving the detector and using a novel state-of-the-art TCSPC electronics we demonstrate by several examples that this composition allows for a reliable control of the bunch timing on a ps scale and a dynamics of up to 10⁷ for bunch purity measurements within complicated fill patterns in a variety of operation modes of the BESSY II storage ring.

We have demonstrated a gated-mode single-photon detector at 1550 nm using two thermoelectrically cooled InGaAs/InP avalanche photodiodes (APDs). Balanced outputs from the two APDs were used to cancel the charge and discharge spikes, which were attributable to capacitive behavior in a gated mode. The avalanche signals were not attenuated during the spike cancellation, which enable one to reduce the bias voltage applied to the APDs and thus reduce the dark count probability. We obtained a quantum efficiency of 10.5% with a dark count probability of 4.8E-5 per gate at 212 K. A single photon detector module that integrated APD and all necessary circuits into a compact bin has been performed.