This PDF file contains the front matter associated with SPIE Proceedings Volume 9504, including the Title Page, Copyright information, Table of Contents, Invited Panel Discussion, and Conference Committee listing.

We demonstrate a 64-pixel free-space-coupled array of superconducting nanowire single photon detectors optimized for high detection efficiency in the near-infrared range. An integrated, readily scalable, multiplexed readout scheme is employed to reduce the number of readout lines to 16. The cryogenic, optical, and electronic packaging to read out the array, as well as characterization measurements are discussed.

A conical tip made out of good conductive metal can be used to efficiently localize the optical field at the apex of the tip. For a tip of finite length both a field singularity (lightning rod effect) and a surface plasmon resonance contribute to the E-field enhancement. A strongly absorbing superconducting nanodetector placed in the optical near-field of the tip shows enhanced optical absorption. The design of an optimal tip- detector system is non-trivial because the strong damping by the detector shifts the resonance wavelength of the tip and significantly lowers the quality factor of the resonance. We compare calculations of the field enhancement of a bare tip to the absorption enhancement in the detector in the presence of the tip as a function of tip length, apex radius and semi-angle of the cone. The resonance of a 225 nm long gold tip in the presence of a detector occurs at ̴1000 nm and is red-shifted by 150 nm compared to the resonance of a bare tip.

Nanostripes of hybrid superconductor/ferromagnetic (S/F) NbN/NiCu bilayers and pure superconducting NbN nanostripes have been investigated in dark count experiments. Presence of a ferromagnetic layer influences the superconducting properties of the S/F bilayer, such as the critical current density and the transient photoresponse. The observed significant decrease of the dark-count rate is discussed in terms of vortex-related fluctuation models to shed more light in the intriguing question of the basic mechanism responsible for dark counts in superconducting nanostripe single photon detectors.

Performance of superconducting single-photon detectors based on resistive hotspot formation in nanostripes upon optical photon absorption depends strongly on the critical current density J_C of the fabricated nanostructure. Utilization of an ultrathin, weak-ferromagnet cap layer on the top of a superconducting film enhances of the structure’s J_C due to an extra flux pinning. We have fabricated a number of both NbN/NiCu and NbTiN/NiCu superconductor/ferromagnet (S/F) ultrathin bilayers and microbridges. NbN and NbTiN underlayers with thicknesses varying from 4 to 7 nm were grown using dc-magnetron sputtering on chemically cleaned sapphire single-crystal substrates. After rapid thermal annealing at high temperatures, the S films were coated with Ni_0.54Cu_0.46 overlayers with thicknesses of about 6 nm, using cosputtering. Compositions of the deposited films were confirmed by EDX spectroscopy analysis, while TEM studies demonstrated excellent epitaxial quality of our S layers with ~2-nm-thick F/S transition layer and atomically-sharp S/substrate interface. Magnetic properties of bilayers were studied using both the SQUID and Vibrating Sample Magnetometer techniques in low and high magnetic fields. Low-temperature tests confirmed that in all cases NiCu films were ferromagnetic with the Curie temperature of above 30 K. Below the bilayer critical temperature of approx. 12-13 K, the structures were fully proximitized with the strong superconducting signal. For superconducting transport properties characterization, we used bilayers patterned into 40-μm-long microbridges with the width varying from 0.4 μm to 2 μm. The same S/F nanostructures were also used to study their superconducting fluctuations. The temperature dependence of magnetoresistance demonstrated highly 2-dimensional character with an unusual negative region that extended almost to room temperature. In the S/F sample, the fluctuations were observed to be substantially below theoretical expectations.

Nanowires of Y-Ba-Cu-O, with the thickness of 50 nm and the width ranging from 90 nm to 500 nm have been successfully grown on lanthanum aluminate substrates for photon detection experiments. The nanowires were up to 10- μm long and formed a meander structure, covering the area of up to 30×10 μm² with a fill factor of 50%. The samples were excited using optical laser pulses at a 1550 nm wavelength and resulting photoresponse signals were measured as a function of both temperature and normalized bias current. Presence of two, distinct regimes in the photoresponse temperature dependence has been clearly evidenced, suggesting different physical mechanisms of the signal formation. Presented experimental results shed new light on prospects of implementation of high-temperature superconducting oxides in photon detection and counting.

We present an ultrafast NbN Superconducting single-photon detector (SSPD) with active area of 3x3 μm², which reveals better timing performances than a previously developed SSPD with active area of 10x10 μm². The improved SSPD demonstrates the record timing jitter <25 ps, ultra short recovery time <2 ns, extremely low dark counts level, and high detection efficiency (DE) in a wide spectral range from visible to near-infrared. The record parameters were obtained thanks to the development of a new technique of an effective optical coupling between a detector with reduced-size active area and a standard single-mode telecommunication fiber. The advantages of a new approach are experimentally confirmed by performed electro-optical measurements of the device performances.

We are presenting the results of research and development of a new active quenching and gating electronics for Single Photon Avalanche Detector (SPAD). The goal of the work was to develop a new SPAD detector package for Laser Time Transfer ground to space with improved timing resolution and stability. The first version of a SPAD detector is operational on board of GNSS navigation satellites. They are based on 25 μm diameter K14 series SPAD chips. They do provide timing resolution of typically 125 ps and stability of the order of 10 ps. The new control electronics provides timing resolution of 25 ps and timing stability and drifts of the order of one picosecond. The device is constructed on a basis of electronics components for which the space qualified equivalents are commercially available. The device construction, tests and results will be presented in detail.

Time correlated photon counting techniques have been proved to be very effective, especially when very fast and faint optical signals have to be recorded with extremely high precision. Nowadays, a steadily increasing number of applications require not only high performance in terms of photon detection efficiency, time resolution and linearity but also a high number of pixels operating in parallel. In order to combine the features of the most performing detectors and state of art timing electronics, an innovative architecture has been conceived and the main circuits have been designed. The system will employ dense arrays of custom technology Single Photon Avalanche Diode (SPAD) detectors, in order to perform a truly concurrent analysis of the sample, while it will have only a small number of acquisition chains with the ultimate purpose of obtaining very high performance while limiting area occupation and power dissipation. To this aim, three main circuits have been designed: first of all, a pick-up circuit capable of directly reading the signal coming from the sensor; secondly, a timing circuit to measure the arrival time of the each photon with picoseconds resolution and very high linearity and finally, a circuit to perform a dynamic binding between the many sensors and the few conversion chains.

The importance of optical time transfer serving as a complement to traditional microwave links, has been attested for GNSSes and for scientific missions. Single photon time transfer (SPTT) is a process, allowing to compare (subtract) time readings of two distant clocks. Such a comparison may be then used to synchronize less accurate clock to a better reference, to perform clock characterization and calibration, to calculate mean time out of ensemble of several clocks, displaced in space. The single-photon time transfer is well established in field of space geodesy, being supported by passive retro-reflectors within space segment of five known GNSSes. A truly two-way, active terminals work aboard of Jason-2 (T2L2) - multiphoton operation, GNSS Beidou (Compass) - SPTT, and are going to be launched within recent ACES project (ELT) - SPTT, and GNSS GLONASS – multiphoton operation. However, there is still missing comprehensive theoretical model of two-way (using satellite receiver and retroreflector) SPTT link incorporating all crucial parameters of receiver (both ground and space segment receivers), transmitter, atmosphere effects on uplink and downlink path, influence of retroreflector. The input to calculation of SPTT link performance will be among others: link budget (distance, power, apertures, beam divergence, attenuation, scattering), propagating medium (atmosphere scintillation, beam wander, etc.), mutual Tx/Rx velocity, wavelength. The SPTT model will be evaluated without the properties of real components. These will be added in the further development. The ground-to-space SPTT link performance of typical scenarios are modeled. This work is a part of the ESA study “Comparison of optical time-transfer links.”

Aqueye+ is a new ultrafast optical single photon counter, based on single photon avalanche photodiodes (SPAD) and a 4- fold split-pupil concept. It is a completely revisited version of its predecessor, Aqueye, successfully mounted at the 182 cm Copernicus telescope in Asiago. Here we will present the new technological features implemented on Aqueye+, namely a state of the art timing system, a dedicated and optimized optical train, a high sensitivity and high frame rate field camera and remote control, which will give Aqueye plus much superior performances with respect to its predecessor, unparalleled by any other existing fast photometer. The instrument will host also an optical vorticity module to achieve high performance astronomical coronography and a real time acquisition of atmospheric seeing unit. The present paper describes the instrument and its first performances.

Arrays of single-photon avalanche diode (SPAD) detectors were fabricated, using a 0.35 μm CMOS technology process, for use in applications such as time-of-flight 3D ranging and microscopy. Each 150 x 150 μm pixel comprises a 30 μm active area diameter SPAD and its associated circuitry for counting, timing and quenching, resulting in a fill-factor of 3.14%. This paper reports how a higher effective fill-factor was achieved as a result of integrating microlens arrays on top of the 32 x 32 SPAD arrays. Diffractive and refractive microlens arrays were designed to concentrate the incoming light onto the active area of each pixel. A telecentric imaging system was used to measure the improvement factor (IF) resulting from microlens integration, whilst varying the f-number of incident light from f/2 to f/22 in one-stop increments across a spectral range of 500-900 nm. These measurements have demonstrated an increasing IF with fnumber, and a maximum of ~16 at the peak wavelength, showing a good agreement with theoretical values. An IF of 16 represents the highest value reported in the literature for microlenses integrated onto a SPAD detector array. The results from statistical analysis indicated the variation of detector efficiency was between 3-10% across the whole f-number range, demonstrating excellent uniformity across the detector plane with and without microlenses.

The LIDAR scanner is at the heart of object detection of the self-driving car. Mutual interference between LIDAR scanners has not been regarded as a problem because the percentage of vehicles equipped with LIDAR scanners was very rare. With the growing number of autonomous vehicle equipped with LIDAR scanner operated close to each other at the same time, the LIDAR scanner may receive laser pulses from other LIDAR scanners. In this paper, three types of experiments and their results are shown, according to the arrangement of two LIDAR scanners. We will show the probability that any LIDAR scanner will interfere mutually by considering spatial and temporal overlaps. It will present some typical mutual interference scenario and report an analysis of the interference mechanism.

Site-specific fluorescence-resonance-energy-transfer donor-acceptor dual-labelled oligonucleotide probes are widely used in state-of-art biotechnological applications. Such applications include their usage as primers in polymerase chain reaction. However, the steady-state fluorescence intensity signal emitted by these molecular tools strongly depends from the specificities of the probe conformation. For this reason, the information which can be reliably inferred by steady-state fluorimetry performed on such samples is forcedly confined to a semi-qualitative level. Namely, fluorescent emission is frequently used as ON/OFF indicator of the probe hybridization state, i.e. detection of fluorescence signals indicates either hybridization to or detachment from the template DNA of the probe. Nonetheless, a fully quantitative analysis of their fluorescence emission properties would disclose other exciting applications of dual-labelled probes in biosensing. Here we show how time-correlated single-photon counting can be applied to get rid of the technical limitations and interpretational ambiguities plaguing the intensity analysis, and to derive information on the template DNA reaching single-base.

SLR (Satellite Laser Ranging) is the common satellite observation technology with the highest single shot precision. The 532nm wavelength laser signal derived from 1064nm wavelength laser system is generally adopted to laser measurement to satellites. The 1064nm wavelength laser signal has better performances than 532nm ones in atmospheric attenuation, photon number, laser power, development and price, and so on, which is beneficial to enhance the detection ability of measuring system, and carry out the goal of weak signal detection. In this paper, the relevant techniques are presented in building up SLR system with 1064nm wavelength, and the corresponding solutions are put forward. With these techniques, the 1064nm wavelength high precise SLR measurement was successfully carried out by using si-detector for the first time in Shanghai Astronomical Observatory (SHAO) and the experimental foundations have been laid for the further development and applications in the field of far distance and weak signal space targets observation.

A multilayer thin-scintillator concept is described for ultrafast imaging. The individual layer thickness is determined by the spatial resolution and light attenuation length, the number of layers is determined by the overall efficiency. By coating the scintillators with a high quantum-efficiency photocathode, single X-ray photon detection can be achieved using fast scintillators with low light yield. The fast, efficient sensors, when combined with MCP and novel nanostructed electron amplification schemes, is a possible way towards GHz hard X-ray cameras for a few frames of images.

The results of computer modeling of the thermoelectric single-photon detector are presented. We observe the processes of heat distribution after absorption of a photon of 0.1-1 keV energy in different parts of the absorber for different geometries of absorbers and thermoelectric sensors. The calculations were carried out by the matrix method for differential equations using parameters for the tungsten absorber and thermoelectric sensor made of (La, Ce)B6. The results of calculations show that it is realistic to detect photons about 0.1-1 keV and determine their energy with accuracy of not less than 1%. High count rates up to 200 GHz can be achieved.

Experimental methodology for parallel measurements of in-vivo skin autofluorescence (AF) lifetimes and photobleaching dynamic has been developed and tested. The AF lifetime decay distributions were periodically collected from fixed tissue area with subsequent detection of the fluorescence intensity decrease dynamic at different time gates after the pulse excitation. Temporal distributions of human in-vivo skin AF lifetimes and bleaching kinetics were collected and analyzed by means of commercial time-correlated single photon counting system.

The report examines key characteristics of the extrafocal images method. This is the extrafocal images detection planes position and a minimum level of difference between the images energy. The method is used for image reconstruction of low-orbit space objects observed through a turbulent atmosphere. The advantage of this method is the ability to restore the image using one frame. Analysis of line of sight shake compensation and a comparison with the method of triple correlations were performed.