This PDF file contains the front matter associated with SPIE Proceedings Volume 12512, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

We propose a protocol for quantum non-demolition photon counting which uses a Rydberg array as a measurement apparatus. Our protocol consists of (I) photon storage, (II) an observation phase comprised of a series of Rabi flops to a Rydberg state and measurements, and (III) retrieval of the stored photons. A detectable signal of the photon number $n$ is provided by the collective enhancement of the Rabi frequency by a factor of $\sqrt{n}$. Our protocol can be used to distill Fock states from arbitrary initial states and to perform photonic state discrimination. We confirm that it is robust to experimentally realistic noise.

Highly-sensitive broadly-tunable detectors are needed for future multi-domain sensing and quantum-information systems. Layered graphene with “magic” twist-angle between 2 - 4 sheets is superconducting below 2 K. Demonstrated Josephson junctions in this material feature very high dynamic resistance at the maximum zero-voltage current. Biased at this current, a small microwave voltage across the junction shifts the voltage-current step, which results in a large DC output voltage. A suitable antenna driven by external radiation can source the desired AC voltage across the junction. As a non-thermal mechanism, such detectors may in principle be fast, as well as sensitive. Additionally, there is a bolometric response, whose temperature coefficient of resistance we estimate to be 300%/K. Design, fabrication, response, and twist-angle tolerance for antenna-coupled, superconducting-graphene, Josephson-junction detectors of mm-wave and THz radiation are discussed.

With the development of advanced and dedicated timing instrumentation, Time-Correlated Single-Photon Counting (TCSPC) has become the de-facto standard for the measurement of low-light signals in a wide variety of applications, from fluorescence observation in biology to 3D scanning in laser ranging. Despite the huge technical improvements, the historical pile-up limitation still represents an open issue, that reduces the maximum acquisition rate to few percent (1-5 %) of the laser excitation rate. This prevents high-speed and real-time exploitation of TCSPC, thus reducing the range of applications that can benefit from such a powerful technique. To overcome this limitation, in 2017 we proposed a novel theoretical approach based on a time-matching between detector dead time and laser period, and in 2021 we designed the first system implementing this new technique. Preliminary results showed a good accordance between the theoretical framework and practical experiments with standard fluorescence dies up to a rate of 32 Mcps. Since then, we have been working on the exploitation of our system in further practical measurements, to perform a deeper validation of its potential. In particular, we have explored the application of our system into a lidar experiment, as no a-priori knowledge is necessary on the specific type of signal. In this proceeding, we present an overview of our work from the theoretical principles to the field verification.

We present a study of the main SPAD figures of merit using a multiscale approach, from Monte Carlo simulations to SPICE simulations. We explore novel stochastic approaches capable of predicting accurately experimental measurements such as the Breakdown Probability, and the jitter. Additionally, the SPAD avalanche dynamics that is a stochastic process, is discussed within a transient Monte Carlo simulation perspective. We also derived a VerilogA model, making possible the analysis of the stochastic responses of the SPAD, including the buildup of the avalanche but also its quench. This latter quench probability of these diodes once in avalanche, rarely discussed in literature, is related to the dynamics of the voltage change of the floating cathode node. If the cathode voltage recovery (after the debiasing due to the quench circuit) is quicker than the time needed for the carrier evacuation within the avalanche junction, small additional avalanches can occur.

Ultraviolet single-photon avalanche detectors (UV-SPADs) that are low cost, size, weight, and power as well as resilient to shock, high temperatures and stray magnetic fields have a number of applications. SiC is attractive for UV SPADs as it is inherently blind to visible light, and Geiger mode as well as high-gain linear-mode devices have been demonstrated. However, issues remain regarding bias dependence of spatial uniformity of detection efficiency (DE) and responsivity as well as the temporal resolution, or jitter, in Geiger mode. Over a wide range of device structures (p- vs. n- illuminated) we observe a non-uniform responsivity across the active area for values of gain from 100 to 10⁵, and we observe that the nonuniformity is somewhat reduced at higher gain. The spatial dependence of the DE in Geiger mode agrees with linear-mode results for gain >10⁵. This presents in all devices as an “optically dead” region on one side of the detector whose extent varies with operating conditions and is independent of contact geometry and device layout. The temporal resolution of single-photon detection is characterized with a femtosecond-pulsed source at 267 nm and found to have a full-width-at-half-maximum jitter < 92 ps, which is significantly lower than previously reported results and likely an upper bound due to the quenching circuit and the spatial non-uniformity. Numerical modeling suggests that small variations in doping densities and thicknesses of epitaxial layers might be a cause of the non-uniformity. Results also indicate that detector layer design, size, and geometry can mitigate the effects of spatial non-uniformity,

Physical models are key tools for developing new SPADs structures. However, as most SPADs characteristics strongly depends on the electric field, a precise knowledge of the doping profile is required. Unfortunately, common profiling techniques are not accurate enough. To cope with this problem, we developed an inverse approach which resorts to the combined use of electrical simulations and capacitance-voltage measurements. We applied the technique to multiple SPADs and we used the extracted profile to calculate their breakdown voltages. Simulated results closely matching the experimental outcomes provide us a strong validation of the proposed extraction technique.

In this paper we report on recent advancements in the development of linear-mode photon-counting (LMPC) electron-initiated avalanche photodiodes (e-APDs) at Leonardo DRS. The Hg1-xCdxTe linear-mode e-APD fills a gap in single-photon detectors from near- to mid-infrared wavelengths and enables several new space lidar and laser communication applications. The combination of high e-APD gain and near unity excess noise factor enables robust, single-photon detection. Another important feature of the Hg_1-xCd_xTe e-APD is that there is no dead time or latency between successive photon detection events. Since the inception of the device, Leonardo DRS has sought to improve the performance of these e-APDs by: increasing linear gains to greater than 1000; decreasing single photon jitter; reducing ROIC glow contributions to dark counts; and decreasing intrinsic detector dark currents. To these ends, we begin by showing that ROIC glow contributions to the false-event rate (FER) can be significantly reduced using an improved, photon blocking shield. We continue by examining the performance of focal-plane arrays (FPAs) with two differing material cutoff wavelengths, demonstrating record low FERs at high photon detection efficiencies (PDEs); this improvement in performance is assisted in part to the successful integration of micro-lens arrays (MLAs) onto the detectors. We conclude our study by integrating one detector unit into a tactical, Integrated Dewar Cooler Assembly (IDCA) and comparing performance prior and following this integration.

Effects of radiation on the dark count rate (DCR) of CMOS single photon avalanche diodes (SPADs) is reviewed. Both total ionizing and non ionizing dose effects are investigated using a test SPAD chip fabricated in a 180 nm CMOS technology as a case study. Models predicting the probability of damage, estimated through the measurement of DCR increase, are also presented. Emphasis is set on the damage dependence on radiation dose and device geometry. Particular attention is paid to the stochastic phenomena taking place in the sensitive volume of SPADs when they are exposed to relatively low fluences (micro-doses) of neutrons.

NASA’s ICESat-2 mission launched in September 2018 carrying a single instrument, the Advanced Topographic Laser Altimeter System (ATLAS). ATLAS uses a high-repetition-rate, low-pulse-energy laser with its output split into six beams and a photon-counting receiver to measure Earth surface elevation with centimeter-level precision, repeating its ground track every 91 days. During more than four years of on-orbit operation, ATLAS has met or exceeded its lifetime and performance requirements. We present performance measurements, trends and projections for several instrument parameter, including transmitted laser pulse energy, receiver sensitivity, the instrument’s impulse response, transmitter/receiver alignment, dead-time behavior, and elevation measurement performance. The laser energy setting was increased in September 2023, for the first time, to maintain ranging performance at its earlymission level. The trends in instrument parameters indicate capability to continue on-orbit operation of ATLAS for many years into the future.

ONERA – The French Aerospace Lab – develops new concepts of 3D-LiDAR imaging systems including new sensor technologies and data processing. Here, we present a more efficient strategy than existing solutions to numerically enhance the lateral resolution of low photon 3D-LiDAR operating in Geiger mode. Our pipeline makes it possible to reconstruct 3D-images with an unprecedented lateral-resolution, simultaneously at low photon count and Hertz level framerates. It is applied on simulated GmAPD 3D-LiDAR signals. Signals acquired using this category of sensors are unsuitable for direct applications of Compressive Sensing algorithms. Our contribution focuses on a more efficient strategy for waveform denoising and reconstruction. For each pixel, we reconstruct sub-pixels by using a Compressive Sensing approach. Compressive Sensing has already been used for single-photon applications with single-pixel cameras. In our pipeline, we extend this method to focal plane arrays in Geiger-mode. This process can be summarized as a set of signal processing techniques to enhance the incoming signal and to improve the Compressive Sensing reconstruction. Our goal is to recover a complete noise-free waveform. We distinguish two main parts: a reconstruction part which compensates the low dynamic range of the signal induced by the Geiger mode; a denoising part which uses a new denoising strategy based on statistical comparisons. This pipeline can be parallelized on GPU, as each pixel in the focal plane array is independent from the others. In this paper, we will detail the pipeline and then demonstrate its applicability on realistic simulated data.

Many Lidar system applications are best implemented with photon-counting sensors such as Geiger-mode avalanche photo diode arrays (GmAPD). To meet this emerging need, SRI has become a merchant supplier for custom GmAPD sensor arrays. SRI is currently building several different custom sensor chip assembly (SCA) designs for our customers. These entirely new sensors are based on our extensive GmAPD design and camera sensor manufacturing experience and designed to address lessons learned in the field. Our objective is to build GmAPD arrays that are truly ready for use in fielded mission critical systems. We report on our development of new ROICS and both planar and mesa type detectors at 1.0um and 1.5um and our packaging, assembly, and testing approach for these new single photon sensitive sensors.

ONERA – The French Aerospace Lab – develops new concepts of 3D-LiDAR imaging systems including new sensor technologies such as detector for photon counting and, associated data processing. The rising complexities and costs of high performance systems, and the shrinking time to design drove the ONERA approach. The home-grown MATLIS software has been evolving for the past decade. It allows both linear mode LiDAR and single photon electro-optical systems simulation (both GmAPD and SPL) embedded on dynamic platforms (eg. UAVs, Aircrafts). The static or dynamic 3D scene is fully described both in terms of geometry and optical properties (eg. reflectance, background illumination, and atmosphere). The scanning system and the platform motion are taken into account. Laser propagation is fully modelled including atmospheric effects such as turbulence, absorption, and backscattering in the forward and backward directions. Target interaction is angle dependent (temporal broadening and directional backscattering). Optical full-wave-form signal is computed in the focal plane of the imaging system. A 3D point cloud is generated using sensor models (including but not limited to APD, GmAPD, SiPM…). Here, we describe our end-to-end MATLIS software and present validation cases. Then, we apply a complete performance analysis study to design a novel and original concept of low-SWaP 3D-LiDAR to detect non-cooperative targets from a stratospheric surveillance platform.

Single photon counting avalanche diodes (SPADs) are versatile sensors for active and time-correlated measurements such as ranging and fluorescence imaging. These detectors also have great potential for passive or uncorrelated imaging. Recently, it was demonstrated that passive imaging of photon flux is possible by determining the mean photon arrival time. For ambient light illumination, timestamp data can be interpreted as a metric for the photon impingement rate. Various applications have been investigated including high-dynamic-range imaging, single-photon imaging, and capture of fast-moving objects or dynamic scenes. However, the appearance of noise and motion blur requires sophisticated signal processing that enables sub-pixel resolution imaging and reconstruction of the scene by motion compensation. In this paper, we present new results on the evaluation of global scene motion. In our approach, motion is intentionally generated by a rotating wedge prism, resulting in continuous global motion on a circular path. We have studied scenes with different optical contrast.