Explore the vast range of titles available.

Hong–Ou–Mandel (HOM) interference—the bunching of indistinguishable photons at a beamsplitter—is a staple of quantum optics and lies at the heart of many quantum sensing approaches and recent optical quantum computers. Here we report a full-field, scan-free quantum imaging technique that exploits HOM interference to reconstruct the surface depth profile of transparent samples. We demonstrate the ability to retrieve images with micrometre-scale depth features with photon flux as small as seven photon pairs per frame. Using a single-photon avalanche diode camera, we measure both bunched and anti-bunched photon-pair distributions at the output of an HOM interferometer, which are combined to provide a lower-noise image of the sample. This approach demonstrates the possibility of HOM microscopy as a tool for the label-free imaging of transparent samples in the very low photon regime.Hong–Ou–Mandel interference enables depth-resolved quantum imaging at very low light levels.

The fast development of mid-wave infrared photonics has increased the demand for high-performance photodetectors that operate in this spectral range. However, the signal-to-noise ratio, regarded as a primary figure of merit for mid-wave infrared detection, is strongly limited by the high dark current in narrow-bandgap materials. Therefore, conventional mid-wave infrared photodetectors such as HgCdTe require cryogenic temperatures to avoid excessively high dark current. To address this challenge, we report an avalanche photodiode design using photon-trapping structures to enhance the quantum efficiency and minimize the absorber thickness to suppress the dark current. The device exhibits high quantum efficiency and dark current density that is nearly three orders of magnitude lower than that of the state-of-the-art HgCdTe avalanche photodiodes and nearly two orders lower than that of previously reported AlInAsSb avalanche photodiodes that operate at 2 µm. Additionally, the bandwidth of these avalanche photodiodes reaches ~7 GHz, and the gain–bandwidth product is over 200 GHz; both are more than four times those of previously reported 2 µm avalanche photodiodes.We demonstrate an avalanche photodiode design using photon-trapping structures to enhance the quantum efficiency and minimizing the absorber thickness, yielding high quantum efficiency, suppressed dark current density and bandwidth of ~7 GHz.

Non-line-of-sight (NLOS) imaging recovers objects using diffusely reflected indirect light using transient illumination devices in combination with a computational inverse method. While capture systems capable of collecting light from the entire NLOS relay surface can be much more light efficient than single pixel point scanning detection, current reconstruction algorithms for such systems have computational and memory requirements that prevent real-time NLOS imaging. Existing real-time demonstrations also use retroreflective targets and reconstruct at resolutions far below the hardware limits. Our method presented here enables the reconstruction of room-sized scenes from non-confocal, parallel multi-pixel measurements in seconds with less memory usage. We anticipate that our method will enable real-time NLOS imaging when used with emerging single-photon avalanche diode array detectors with resolution only limited by the temporal resolution of the sensor. Current implementations of non-line-of-sight imaging use reconstruction algorithms that are difficult to implement fast enough for real-time application using light efficient equipment. The authors present an algorithm for non-line-of-sight imaging that is low complexity and allows fast and efficient reconstruction on a standard computer.

A photon avalanche (PA) effect that occurs in lanthanide-doped solids gives rise to a giant nonlinear response in the luminescence intensity to the excitation light intensity. As a result, much weaker lasers are needed to evoke such PAs than for other nonlinear optical processes. Photon avalanches are mostly restricted to bulk materials and conventionally rely on sophisticated excitation schemes, specific for each individual system. Here we show a universal strategy, based on a migrating photon avalanche (MPA) mechanism, to generate huge optical nonlinearities from various lanthanide emitters located in multilayer core/shell nanostructrues. The core of the MPA nanoparticle, composed of Yb 3+ and Pr 3+ ions, activates avalanche looping cycles, where PAs are synchronously achieved for both Yb 3+ and Pr 3+ ions under 852 nm laser excitation. These nanocrystals exhibit a 26th-order nonlinearity and a clear pumping threshold of 60 kW cm −2 . In addition, we demonstrate that the avalanching Yb 3+ ions can migrate their optical nonlinear response to other emitters (for example, Ho 3+ and Tm 3+ ) located in the outer shell layer, resulting in an even higher-order nonlinearity (up to the 46th for Tm 3+ ) due to further cascading multiplicative effects. Our strategy therefore provides a facile route to achieve giant optical nonlinearity in different emitters. Finally, we also demonstrate applicability of MPA emitters to bioimaging, achieving a lateral resolution of ~62 nm using one low-power 852 nm continuous-wave laser beam. A general mechanism, migrating photon avalanche, can generate large optical nonlinearity from various lanthanides emitters at the nanoscale.

Single-photon detection has emerged as a method of choice for ultra-sensitive measurements of picosecond optical transients. In the short-wave infrared, semiconductor-based single-photon detectors typically exhibit relatively poor performance compared with all-silicon devices operating at shorter wavelengths. Here we show a new generation of planar germanium-on-silicon (Ge-on-Si) single-photon avalanche diode (SPAD) detectors for short-wave infrared operation. This planar geometry has enabled a significant step-change in performance, demonstrating single-photon detection efficiency of 38% at 125 K at a wavelength of 1310 nm, and a fifty-fold improvement in noise equivalent power compared with optimised mesa geometry SPADs. In comparison with InGaAs/InP devices, Ge-on-Si SPADs exhibit considerably reduced afterpulsing effects. These results, utilising the inexpensive Ge-on-Si platform, provide a route towards large arrays of efficient, high data rate Ge-on-Si SPADs for use in eye-safe automotive LIDAR and future quantum technology applications. By incorporating germanium, single-photon avalanche diode detectors using silicon-based platforms are applied to infrared light detection. Here, a cost-effective planar detector geometry is presented yielding high detection efficiency suitable for applications such as sparse photon imaging or LIDAR.

Non-Line-Of-Sight (NLOS) imaging aims at recovering the 3D geometry of objects that are hidden from the direct line of sight. One major challenge with this technique is the weak available multibounce signal limiting scene size, capture speed, and reconstruction quality. To overcome this obstacle, we introduce a multipixel time-of-flight non-line-of-sight imaging method combining specifically designed Single Photon Avalanche Diode (SPAD) array detectors with a fast reconstruction algorithm that captures and reconstructs live low-latency videos of non-line-of-sight scenes with natural non-retroreflective objects. We develop a model of the signal-to-noise-ratio of non-line-of-sight imaging and use it to devise a method that reconstructs the scene such that signal-to-noise-ratio, motion blur, angular resolution, and depth resolution are all independent of scene depth suggesting that reconstruction of very large scenes may be possible. Non-line-of-sight imaging can recover the 3D geometry of hidden objects, but is limited by weak multibounce signals. Here, the authors introduce a multipixel time-of-flight NLOS imaging approach, combining array detectors and a fast algorithm, for live reconstruction of natural nonretroreflective objects.

Optical imaging techniques, such as light detection and ranging (LiDAR), are essential tools in remote sensing, robotic vision, and autonomous driving. However, the presence of scattering places fundamental limits on our ability to image through fog, rain, dust, or the atmosphere. Conventional approaches for imaging through scattering media operate at microscopic scales or require a priori knowledge of the target location for 3D imaging. We introduce a technique that co-designs single-photon avalanche diodes, ultra-fast pulsed lasers, and a new inverse method to capture 3D shape through scattering media. We demonstrate acquisition of shape and position for objects hidden behind a thick diffuser (≈6 transport mean free paths) at macroscopic scales. Our technique, confocal diffuse tomography, may be of considerable value to the aforementioned applications. Techniques for imaging through scattering media are generally invasive, operate at microscopic scales or require a priori information. Here, the authors overcome these limitations by introducing confocal diffuse tomography, which captures the 3D shape of objects hidden behind scattering media.

The ability to detect single photons has led to the advancement of numerous research fields 1 – 11 . Although various types of single-photon detector have been developed 12 , because of two main factors—that is, (1) the need for operating at cryogenic temperature 13 , 14 and (2) the incompatibility with complementary metal–oxide–semiconductor (CMOS) fabrication processes 15 , 16 —so far, to our knowledge, only Si-based single-photon avalanche diode (SPAD) 17 , 18 has gained mainstream success and has been used in consumer electronics. With the growing demand to shift the operation wavelength from near-infrared to short-wavelength infrared (SWIR) for better safety and performance 19 – 21 , an alternative solution is required because Si has negligible optical absorption for wavelengths beyond 1 µm. Here we report a CMOS-compatible, high-performing germanium–silicon SPAD operated at room temperature, featuring a noise-equivalent power improvement over the previous Ge-based SPADs 22 – 28 by 2–3.5 orders of magnitude. Key parameters such as dark count rate, single-photon detection probability at 1,310 nm, timing jitter, after-pulsing characteristic time and after-pulsing probability are, respectively, measured as 19 kHz µm −2 , 12%, 188 ps, ~90 ns and <1%, with a low breakdown voltage of 10.26 V and a small excess bias of 0.75 V. Three-dimensional point-cloud images are captured with direct time-of-flight technique as proof of concept. This work paves the way towards using single-photon-sensitive SWIR sensors, imagers and photonic integrated circuits in everyday life. A germanium–silicon single-photon avalanche diode operated at room temperature shows a noise-equivalent power improvement over the previous Ge-based single-photon avalanche diodes by 2–3.5 orders of magnitude.

Materials whose luminescence can be switched by optical stimulation drive technologies ranging from superresolution imaging 1 – 4 , nanophotonics 5 , and optical data storage 6 , 7 , to targeted pharmacology, optogenetics, and chemical reactivity 8 . These photoswitchable probes, including organic fluorophores and proteins, can be prone to photodegradation and often operate in the ultraviolet or visible spectral regions. Colloidal inorganic nanoparticles 6 , 9 can offer improved stability, but the ability to switch emission bidirectionally, particularly with near-infrared (NIR) light, has not, to our knowledge, been reported in such systems. Here, we present two-way, NIR photoswitching of avalanching nanoparticles (ANPs), showing full optical control of upconverted emission using phototriggers in the NIR-I and NIR-II spectral regions useful for subsurface imaging. Employing single-step photodarkening 10 – 13 and photobrightening 12 , 14 – 16 , we demonstrate indefinite photoswitching of individual nanoparticles (more than 1,000 cycles over 7 h) in ambient or aqueous conditions without measurable photodegradation. Critical steps of the photoswitching mechanism are elucidated by modelling and by measuring the photon avalanche properties of single ANPs in both bright and dark states. Unlimited, reversible photoswitching of ANPs enables indefinitely rewritable two-dimensional and three-dimensional multilevel optical patterning of ANPs, as well as optical nanoscopy with sub-Å localization superresolution that allows us to distinguish individual ANPs within tightly packed clusters. This study reports unlimited near-infrared photoswitching in inorganic avalanching nanoparticles via a discrete shift of threshold intensity mediated by internal defect-based colour centres.

Colloidal quantum dots (CQDs) are promising for infrared photodetectors with high detectivity and low-cost production. Although CQDs enable photoinduced charge multiplication, thermal noise in low-bandgap materials limits their performance in IR detectors. Here we present a pioneering architecture of a CQD-based infrared photodetector that uses kinetically pumped avalanche multiplication. By applying a strong electric field to a thick CQD layer (>540 nm), electrons acquire kinetic energy beyond the bandgap of the CQD material, initiating kinetically pumped charge multiplication. Optimizing the dot-to-dot distance to approximately 4.1 nm improves performance by balancing impact ionization and electron hopping. Our optimized CQD-based infrared photodetector achieved a maximum multiplication gain of 85 and a peak detectivity of 1.4 × 10 14  Jones at 940 nm. This architecture offers potential for single-photon detection and ultrahigh detectivity applications. Kinetically pumped avalanche multiplication has been demonstrated in a colloidal quantum dot photodetector, achieving an 85-fold multiplication gain. This proposes new opportunities for developing colloidal quantum dot single-photon detectors.