Single-photon Sensitivity Research Articles

Non-fusion time-resolved depth image reconstruction using a highly efficient neural network architecture.

Single-photon avalanche diodes (SPAD) are powerful sensors for 3D light detection and ranging (LiDAR) in low light scenarios due to their single-photon sensitivity. However, accurately retrieving ranging information from noisy time-of-arrival (ToA) point clouds remains a challenge. This paper proposes a photon-efficient, non-fusion neural network architecture that can directly reconstruct high-fidelity depth images from ToA data without relying on other guiding images. Besides, the neural network architecture was compressed via a low-bit quantization scheme so that it is suitable to be implemented on embedded hardware platforms. The proposed quantized neural network architecture achieves superior reconstruction accuracy and fewer parameters than previously reported networks.

Miniaturized USB-powered multi-channel module for gamma spectroscopy and imaging

LAILA is a miniaturized eight-channel electronic readout system for compact γ-ray detectors, combining high-resolution spectroscopy capability with position sensitivity. Compactness is achieved by the combination of a novel CMOS front-end ASIC (Application-Specific Integrated Circuit) for analog processing of a large signal current from Silicon PhotoMultiplier (SiPM) solid-state photodetectors, with a microcontroller-based data acquisition system. The adoption of automatic gain regulation in the gated-integrator stage of the ASIC offers an 84 dB dynamic range, combining single-photon sensitivity with an extended input photon energy range (20 keV-4MeV, using 30 μm-cell SiPMs). Using this module with properly merged 144 SiPM pixels coupled to a 3 in.-thick lanthanum bromide scintillation crystal, a 3% energy resolution at 662 keV and 1cm spatial resolution in the estimation of the interaction coordinates are experimentally demonstrated in this work.

Infrared single-photon sensitivity in atomic layer deposited superconducting nanowires

We report on the extended infrared single-photon response of niobium nitride superconducting nanowires deposited by atomic layer deposition. The superconducting nanowire single-photon detectors are based on 4.65 nm thick NbN, patterned into 100 nm meanders, and characterized at 2.5 K. We verify single-photon sensitivity from 1310 to 2006 nm with saturated response at shorter wavelengths.

Advantages of a curved image plate for rapid laboratory-based x-ray total scattering measurements: Application to pair distribution function analysis.

The analysis and interpretation of the pair distribution function (PDF), as derived from total scattering measurements, is still seen by many as a technique confined to central synchrotron and neutron facilities. This situation has begun to change with a rising visibility of total scattering experiments reported in mainstream scientific journals and the modification of an increasing number of laboratory diffractometers. However, the rigor required during data reduction and the complexities of data interpretation mean the technique is still very far from being routine. Herein, we report the first application of a large area curved image plate system based on a Rigaku SPIDER (R-AXIS RAPID II) equipped with an Ag tube for collecting data amenable to high quality PDF refinement/modeling of crystalline, amorphous, and liquid samples. The advantages of such a system are the large Q range available without scanning (routinely in excess of 20 Å-1) and the inherent properties of an image plate detector (single photon sensitivity, large dynamic range [1.05 × 106], and effectively zero noise). Data are collected and structural models refined for a number of standard materials including NIST 640f silicon for which a Rwp ≤ 0.12 value was obtained with data collected in 60min (excluding background measurements). These and other data are discussed and compared to similar examples in the literature.

Design and first tests of the Gotthard-II readout ASIC for the European X-ray Free-Electron Laser

Gotthard-II is a charge-integrating microstrip detector developed for experiments and diagnostics at free-electron lasers using hard X-rays of 5 keV–20 keV. Thanks to its excellent single photon sensitivity, large dynamic range as well as high frame rate of 4.5 MHz in burst mode, its potential scientific applications include X-ray absorption/emission spectroscopy, hard X-ray high resolution single-shot spectrometry (HiREX), beam diagnostics, as well as veto signal generation for pixel detectors. The Gotthard-II ASIC has been designed and fabricated using UMC-110 nm technology. The final ASIC design and performance in terms of noise, linearity, dynamic range, coupling between channels and speed will be discussed in the paper. In addition, a first measurement of an X-ray absorption spectrum of a standard copper sample has been done. The performance of the Gotthard-II in an experiment using energy dispersive X-rays has been demonstrated.

Sensitive single-photon test of extended quantum theory with two-dimensional hexagonal boron nitride

Quantum theory is the foundation of modern physics. Some of its basic principles, such as Born's rule, however, are based on postulates which require experimental testing. Any deviation from Born's rule would result in higher-order interference and can thus be tested in an experiment. Here, we report on such a test with a quantum light source based on a color center in hexagonal boron nitride (hBN) coupled to a microcavity. Our room temperature photon source features a narrow linewidth, high efficiency, high purity, and on-demand single-photon generation. With the single-photon source we can increase the interferometric sensitivity of our three-path interferometer compared to conventional laser-based light sources by fully suppressing the detector nonlinearity. We thereby obtain a tight bound on the third-order interference term of $3.96(523)\times 10^{-4}$. We also measure an interference visibility of 98.58% for our single-photons emitted from hBN at room temperature, which provides a promising route for using the hBN platform as light source for phase-encoding schemes in quantum key distribution.

Concepts for the XIDer readout ASIC incorporating a pipelined ADC with very low dead time

We present the first concept for the analog front-end of the readout ASIC for the XIDer (X-ray Integrating Detector) detector system which is beingdeveloped by a collaboration between the ESRF and Heidelberg University. The ESRF's Extremely Brilliant Source (EBS) upgrade which has been completed recently provides X-ray beams of unprecedentedquality, requiring new photon detection instruments. The XIDer project has been launched to developa new versatile pixel detector which will be tailored to match requirements imposed by this upgrade. The core challengesinclude fast signal acquisition, large dynamic range and single photon sensitivity. A firstprototype ASIC for the analog front-end of a single pixel has been manufactured. It is based on a pipelined two-stage charge removal circuit which digitizes the incident signal on the fly. We will present measurement results of the first test chip and concepts for the final system-on-chip implementation integrating several tens of thousands of pixels.

Compact long-range single-photon imager with dynamic imaging capability.

Single-photon light detection and ranging (LiDAR) has emerged as a strong candidate technology for active imaging applications. Benefiting from the single-photon sensitivity in detection, long-range active imaging can be realized with a low-power laser and a small-aperture transceiver. However, existing kilometer-range active imagers are bulky and have a long data acquisition time. Here we present a compact co-axial single-photon LiDAR system for kilometer-range 3D imaging. A fiber-based transceiver with a 2.5 cm effective aperture was employed to realize a robust and compact architecture, while a tailored temporal filtering approach guaranteed the high signal-to-noise level. Moreover, a micro-electro-mechanical system scanning mirror was adopted to achieve fast beam scanning. In experiment, high-resolution 3D images of different targets up to 12.8 km were acquired to demonstrate the long-range imaging capability. Furthermore, it exhibits the ability to achieve dynamic imaging at five frames per second over a distance of ∼1km. The results indicate potential in a variety of applications such as remote sensing and long-range target detection.

Remote eavesdropping at 200 meters distance based on laser feedback interferometry with single-photon sensitivity

A remote eavesdropping system based on the laser feedback interferometry is proposed. The diffuse objects neighboring the speaker can work as inconspicuous sensors. The modulated incident beam is scattered back to the laser cavity by the objects, forming the self-mixing interference. The huge amplification caused by the self-mixing interference provides the system with ultra-high sensitivity, even the feedback light whose intensity is -104dB lower than the laser output can still be sensed. The comprehensible voice reconstruction of the object at the distance of 200 m can be realized, although only 0.91 photon in each interference modulation cycle is scattered back into the laser cavity. Additionally, the range of the incident angle of the beam can be up to ±45 deg, and the optimal one is ±30 deg. This system can meet various requirements of acoustic signals detection and be potentially applied in fields as disaster relief and remote surveillance.

Novel imaging technique for α-particles using a fast optical camera

A new imaging technique for α-particles using a fast optical camera focused on a thin scintillator is presented. As α-particles interact in a thin layer of LYSO fast scintillator, they produce a localized flash of light. The light is collected with a lens to an intensified optical camera, Tpx3Cam, with single photon sensitivity and excellent spatial & temporal resolutions. The interactions of photons with the camera is reconstructed by means of a custom algorithm, capable of discriminating single photons using time and spatial information.

Mid-infrared photon counting and resolving via efficient frequency upconversion

Optical detectors with single-photon sensitivity and large dynamic range would facilitate a variety of applications. Specifically, the capability of extending operation wavelengths into the mid-infrared region is highly attractive. Here we implement a mid-infrared frequency upconversion detector for counting and resolving photons at 3 μm. Thanks to the spectrotemporal engineering of the involved optical fields, the mid-infrared photons could be spectrally translated into the visible band with a conversion efficiency of 80%. In combination with a silicon avalanche photodiode, we obtained unprecedented performance with a high overall detection efficiency of 37% and a low noise equivalent power of 1.8 × 10 − 17 W / Hz 1 / 2 . Furthermore, photon-number-resolving detection at mid-infrared wavelengths was demonstrated, for the first time to our knowledge, with a multipixel photon counter. The implemented upconversion detector exhibited a maximal resolving photon number up to 9 with a noise probability per pulse of 0.14% at the peak detection efficiency. The achieved photon counting and resolving performance might open up new possibilities in trace molecule spectroscopy, sensitive biochemical sensing, and free-space communications, among others.

Temperature dependency of InGaAs/InP single photon avalanche diode for 1 550 nm photons

Single-photon detectors for the near-infrared wavelength region are receiving widespread attention in an increasing number of photon counting applications. In fields such as quantum information processing, quantum communication, 3-D laser ranging (LiDAR), time-resolved spectroscopy, etc. An InGaAs/InP single photon avalanche diode (SPAD) was designed and demonstrated to detect 1 550 nm wavelength photons in this paper. The SPAD has a separate absorption, grading, charge and multiplication region structure (SAGCM) with single photon sensitivity when working in Geiger-mode. The characterization of the SPAD include breakdown voltage, dark count rate, single photon detection efficiency and after pulse probability as functions of temperature from 223 to 293 K. The 25 μm diameter SPAD shows certain temperature dependency, with breakdown voltage dependence of approximately 100 mV/K. Operating at 223 K and in Geiger-mode, the SPAD achieves a photon detection efficiency of 21% at 1 550 nm with a dark count rate of 4.1 kHz and a after pulse probability of 3.29%. The source and physical mechanism of the photon detection efficiency, dark count rate and after pulse probability of the SPAD with temperature dependency were also analyzed and discussed. The mechanism analysis, discussion and calculation can provide more theoretical basis and support for the design and fabrication of SPAD.

Mapping the Photoresponse of the Quantum-Dot Based Photon-Number-Resolving Detector

Efficient and versatile photon-number resolving detectors are critical to the development of future communication systems. The quantum-dot, optically-gated, field-effect transistor (QDOGFET) is one such detector. Utilizing quantum dots (QDs), tiny islands of semiconductor, imbedded in a transistor, QDOGFETs have been shown to exhibit single-photon sensitivity and photon-number-resolving (PNR) capabilities. A photon is detected when it photocharges a QD, which alters the amount of current flowing through the transistor by screening the gate field. Crucial to the resolving power is that each charged QD produce the same response, regardless of its location within the active area of the device. Here, we investigate the extent spatial nonuniformities in the QDOGFET’s response to light limit its ability to distinguish different numbers of photons. By using an optical-scanning microscope (OSM), contour plots of a QDOGFET’s response are acquired that show that the device exhibits localized “hotspots” where it is particularly sensitive to photons. The spatial resolution of the microscope is enhanced by capping the QDOGFET with a solid-immersion lens (SIL). We present experimental results that show how the hotspots depend on bias conditions and help decipher the root cause of the nonuniformities.

Single-Photon Imaging Goes Long Range

Single-photon sensitivity and picosecond time resolution are desirable for long-range imaging in a variety of applications. In recent experiments, we were able to substantially exceed the previous single-photon-imaging range record, demonstrating single-photon 3D imaging at a range of up to 45 km in urban environments.

Time-resolved RIXS experiment with pulse-by-pulse parallel readout data collection using X-ray free electron laser

Time-resolved resonant inelastic X-ray scattering (RIXS) is one of the developing techniques enabled by the advent of X-ray free electron laser (FEL). It is important to evaluate how the FEL jitter, which is inherent in the self-amplified spontaneous emission process, influences the RIXS measurement. Here, we use a microchannel plate (MCP) based Timepix soft X-ray detector to conduct a time-resolved RIXS measurement at the Ti L3-edge on a charge-density-wave material TiSe2. The fast parallel Timepix readout and single photon sensitivity enable pulse-by-pulse data acquisition and analysis. Due to the FEL jitter, low detection efficiency of spectrometer, and low quantum yield of RIXS process, we find that less than 2% of the X-ray FEL pulses produce signals, preventing acquiring sufficient data statistics while maintaining temporal and energy resolution in this measurement. These limitations can be mitigated by using future X-ray FELs with high repetition rates, approaching MHz such as the European XFEL in Germany and LCLS-II in the USA, as well as by utilizing advanced detectors, such as the prototype used in this study.

Molecular Platform for Frequency Upconversion at the Single-Photon Level

Direct detection of single photons at wavelengths beyond 2 microns under ambient conditions remains an outstanding technological challenge. One promising approach is frequency upconversion into the visible (VIS) or near-infrared (NIR) domain, where single photon detectors are readily available. Here, we propose a nanoscale solution based on a molecular optomechanical platform to up-convert photons from the far and mid-infrared (covering part of the THz gap) into the VIS-NIR domain. We perform a detailed analysis of its outgoing noise spectral density and conversion efficiency with a full quantum model. Our platform consists in doubly resonant nanoantennas focusing both the incoming long-wavelength radiation and the short-wavelength pump laser field into the same active region. There, infrared active vibrational modes are resonantly excited and couple through their Raman polarizability to the pump field. This optomechanical interaction is enhanced by the antenna and leads to the coherent transfer of the incoming low-frequency signal onto the anti-Stokes sideband of the pump laser. Our calculations demonstrate that our scheme is realizable with current technology and that optimized platforms can reach single photon sensitivity in a spectral region where this capability remains unavailable to date.

Single-photon computational 3D imaging at 45 km

Single-photon light detection and ranging (lidar) offers single-photon sensitivity and picosecond timing resolution, which is desirable for high-precision three-dimensional (3D) imaging over long distances. Despite important progress, further extending the imaging range presents enormous challenges because only a few echo photons return and are mixed with strong noise. Here, we tackled these challenges by constructing a high-efficiency, low-noise coaxial single-photon lidar system and developing a long-range-tailored computational algorithm that provides high photon efficiency and good noise tolerance. Using this technique, we experimentally demonstrated active single-photon 3D imaging at a distance of up to 45 km in an urban environment, with a low return-signal level of ∼ 1 photon per pixel. Our system is feasible for imaging at a few hundreds of kilometers by refining the setup, and thus represents a step towards low-power and high-resolution lidar over extra-long ranges.

Assessment of the potential of SiPM-based systems for bioluminescence detection

Bioluminescence detection requires single-photon sensitivity, extremely low detection limits and wide dynamic range. Such performances were traditionally assured by photomultiplier-tubes based systems. However, development of novel applications and industrialization call for the introduction of more robust, compact and scalable devices. Silicon photomultipliers were recently put forward as the alternative to phototubes for a new generation of flexible and user friendly instruments. In this article, the figures of merit of a silicon-photomultiplier based system relying on a compact, low cost system are investigated. Possible implementations are proposed and a proof-of-principle bioluminescence measurement is performed.

Assessment of a Silicon-Photomultiplier-Based Platform for the Measurement of Intracellular Calcium Dynamics with Targeted Aequorin.

Ca2+ is among the most important intracellular second messengers participating in a plethora of biological processes, and the measurement of Ca2+ fluctuations is significant in the phenomenology of the underlying processes. Aequorin-based Ca2+ probes represent an invaluable tool for reliable measurement of Ca2+ concentrations and dynamics in different subcellular compartments. However, their use is limited due to the lack on the market of ready-to-use, cost-effective, and portable devices for the detection and readout of the low-intensity bioluminescence signal produced by these probes. Silicon photomultipliers (SiPMs) are rapidly evolving solid-state sensors for low light detection, with single photon sensitivity and photon number resolving capability, featuring low cost, low voltage, and compact format. Thus, they may represent the sensors of choice for the development of such devices and, more in general, of a new generation of multipurpose bioluminescence detectors suitable for cell biology studies. Ideally, a detector customized for these purposes must combine high dynamic range with high fidelity in reconstructing the light intensity signal temporal profile. In this article, the ability to perform aequorin-based intracellular Ca2+ measurements using a multipurpose, low-cost setup exploiting SiPMs as the sensors is demonstrated. SiPMs turn out to assure performances comparable to those exhibited by a custom-designed photomultiplier tube-based aequorinometer. Moreover, the flexibility of SiPM-based devices might pave the way toward routinely and wide scale application of innovative biophysical protocols.

Single-Photon Detectors Modeling and Selection Criteria for High-Background LiDAR

Vision systems capable of acquiring both two-dimensional and three-dimensional information through Light Detection And Ranging are assuming ever-increasing importance, being this market driven by the push from automotive companies to develop systems to be integrated in self-driving vehicles. Among others, candidate sensors for these systems are avalanche photodiodes, single-photon avalanche diodes, and silicon photomultipliers. Avalanche Photodiodes provide a good robustness to high background light at the cost of requiring an analog readout, instead Single-Photon Avalanche Diodes offer the possibility to implement digital readout and single-photon sensitivity, but are prone to saturation at extremely high background levels. We compare these three single- and multi-photon detector topologies, operated either in linear or digital regime, aiming at identifying the best suited detector to achieve the highest performance in Light Detection And Ranging applications at the lowest optical power active illumination and in presence of intense background (e.g. 100 klux). We present Matlab modelling and simulations and their experimental validation. Eventually, we propose a nomogram (referred to 100 m target distance) for identifying the most suited sensor topology across different operating areas and constraints, in order to achieve at least 70% success ratio.