Ultra-low Light Levels Research Articles

A real-time ultra-low light color imaging system based on FPGA

This article shows a low light color image acquisition system, The core components of the system are the Fairchild’s SCMOS image sensor CIS1910F1111 and XILINX’s Artix-7 XC7A100T-2CSG324I FPGA, the remarkable advantage of the system is that it can obtain better color imaging effect under lower illumination environment, and the image noise is much less than other similar products. Based on the excellent imaging performance of the image detector, a high performance real-time low-light level color imaging system is developed. This imaging system can obtain the characteristic information of the targets under ultra-low illuminance environment, including the details, colors and so on. The hardware of the low light level imaging system mainly contains a color SCMOS image sensor and a FPGA, a driving circuit of a combination of DDR3, the ultra-low noise power conversion circuit and a Camera-Link and a 3G-SDI interface circuits. The SCMOS chip is used for photoelectric conversion of the shot scene and the FPGA is used for the control of the whole imaging system, image acquisition and image processing, etc, The FPGA software system consists of SCMOS initialize configuration and timing control module, automatic exposure control module, real-time color image processing module, imaging tone mapping module, image denoising module and image enhancement module. The automatic exposure control (AEC) module adaptively adjusts the average gray value of the region of interest. The module automatically calculates the exposure time and gain value of the next frame according to the current frame image data value. The real-time color image processing module includes color restoration, automatic white balance and color spaces conversion, etc. The image denoising module uses the advanced real-time guide-filter algorithm. The image tone mapping module and enhancement module are proposed based on an improved automatic threshold logarithmic and enhancement algorithm. Combining the hardware and FPGA soft algorithm with excellent performance, the imaging results show that the system can get good color image effect of the ultra-low light level about 10-2lx.

Mutual coupling and synchronization of optically coupled quantum-dot micropillar lasers at ultra-low light levels

Synchronization of coupled oscillators at the transition between classical physics and quantum physics has become an emerging research topic at the crossroads of nonlinear dynamics and nanophotonics. We study this unexplored field by using quantum dot microlasers as optical oscillators. Operating in the regime of cavity quantum electrodynamics (cQED) with an intracavity photon number on the order of 10 and output powers in the 100 nW range, these devices have high β-factors associated with enhanced spontaneous emission noise. We identify synchronization of mutually coupled microlasers via frequency locking associated with a sub-gigahertz locking range. A theoretical analysis of the coupling behavior reveals striking differences from optical synchronization in the classical domain with negligible spontaneous emission noise. Beyond that, additional self-feedback leads to zero-lag synchronization of coupled microlasers at ultra-low light levels. Our work has high potential to pave the way for future experiments in the quantum regime of synchronization.

Laser Acupuncture in Open-Angle Glaucoma Treatment: A Retrospective Study of Eye Blood Flow

Patients with glaucoma can show blood flow anomalies at the eye vessel level. A causal relationship is reasonably expected, but so far, it has not been demonstrated. Traditional Chinese medicine indicates that acupuncture can promote specific blood perfusion in specific body districts. Ninety-eight patients with open-angle glaucoma were treated with an ultralow light–level laser, according to a specific acupuncture protocol, and their blood flow was measured before and after a six-week treatment cycle. Doppler measurements showed significant modifications in both pulsatility and resistivity indexes. The most relevant outcome of this study is that the applied treatment demonstrated its effectiveness not only in vasodilation but also in perfusion control that seems to restore appropriate functionality. The protocol therefore should be investigated in future controlled studies and perhaps in other blood perfusion–related pathologies.

Highly Efficient Rubrene-Graphene Charge-Transfer Interfaces as Phototransistors in the Visible Regime.

Atomically thin materials such as graphene are uniquely responsive to charge transfer from adjacent materials, making them ideal charge-transport layers in phototransistor devices. Effective implementation of organic semiconductors as a photoactive layer would open up a multitude of applications in biomimetic circuitry and ultra-broadband imaging but polycrystalline and amorphous thin films have shown inferior performance compared to inorganic semiconductors. Here, the long-range order in rubrene single crystals is utilized to engineer organic-semiconductor-graphene phototransistors surpassing previously reported photogating efficiencies by one order of magnitude. Phototransistors based upon these interfaces are spectrally selective to visible wavelengths and, through photoconductive gain mechanisms, achieve responsivity as large as 107 A W-1 and a detectivity of 9 × 1011 Jones at room temperature. These findings point toward implementing low-cost, flexible materials for amplified imaging at ultralow light levels.

Performance of hydrogenated amorphous silicon thin film photosensors at ultra-low light levels: towards attomole sensitivities in labon- chip biosensing applications

Thin-film optical transducers integrated in lab-on-a-chip (LoC) devices have the potential to facilitate miniaturization, multiplexing capabilities, portability, and sensitivity. However, there are few systematic studies that provide detailed characterization of these photosensors to particular miniaturized bioassays at reduced light intensities. A more detailed representation of the photosensors performance at low light levels is thus needed in order to improve the engineering of integrated detectors for the next generation of portable biosensors. Here, an assessment of the performance of hydrogenated amorphous silicon (a-Si:H) photosensors, at ultra-low light intensity, based on two different device configurations for integration in a microfluidic platform for biomolecular detection is presented. Both p-i-n photodiodes and parallel contact photoconductors show low dark current density (~10−10 A.cm−2) and photosensitivity comparable with high performing crystalline silicon photosensors. The a-Si:H photosensors were integrated in microfluidic devices for the detection of antibody-horseradish peroxidase conjugates (Ab-HRP) in a chemiluminescence-based assay. Surface concentrations of Ab-HRP as low as ~26 amol.cm−2 and ~9 fmol.cm−2 (corresponding to ~103 and ~106 HRP molecules) were detected with detectors in photodiode and photoconductor configurations, respectively, with the sensitivity of the former being comparable with that of bulky and ultra-sensitive photomultiplier tubes. The excellent sensitivity and dynamic range obtained, together with the miniaturization and arraying potential, highlight the potential of a-Si:H photosensors as an effective means of integrating the multiplexed acquisition of optical data in real time in point-of-need LoC systems.

Ultralow-light-level all-optical transistor in rubidium vapor

An all-optical transistor (AOT) is a device in which one light beam can efficiently manipulate another. It is the foundational component of an all-optical communication network. An AOT that can operate at ultralow light levels is especially attractive for its potential application in the quantum information field. Here, we demonstrate an AOT driven by a weak light beam with an energy density of 2.5 × 10−5 photons/(λ2/2π) (corresponding to 6 yJ/(λ2/2π) and about 800 total photons) using the double-Λ four-wave mixing process in hot rubidium vapor. This makes it a promising candidate for ultralow-light-level optical communication and quantum information science.

Photon counting compressive depth mapping

We demonstrate a compressed sensing, photon counting lidar system based on the single-pixel camera. Our technique recovers both depth and intensity maps from a single under-sampled set of incoherent, linear projections of a scene of interest at ultra-low light levels around 0.5 picowatts. Only two-dimensional reconstructions are required to image a three-dimensional scene. We demonstrate intensity imaging and depth mapping at 256 × 256 pixel transverse resolution with acquisition times as short as 3 seconds. We also show novelty filtering, reconstructing only the difference between two instances of a scene. Finally, we acquire 32 × 32 pixel real-time video for three-dimensional object tracking at 14 frames-per-second.

Ultra-low power, Zeno effect based optical modulation in a degenerate V-system with a tapered nano fiber in atomic vapor

We demonstrate an ultra-low light level optical modulator using a tapered nano fiber embedded in a hot rubidium vapor. The control and signal beams are co-propagating but orthogonally polarized, leading to a degenerate V-system involving coherent superpositions of Zeeman sublevels. The modulation is due primarily to the quantum Zeno effect for the signal beam induced by the control beam. For a control power of 40 nW and a signal power of 100 pW, we observe near 100% modulation. The ultra-low power level needed for the modulation is due to a combination of the Zeno effect and the extreme field localization in the evanescent field around the taper.

Latest bialkali photocathode with ultra high sensitivity

Among photosensitive devices in use today, the photomultiplier tube (PMT) is a versatile device providing extremely high sensitivity, exceptionally low noise and ultra-fast response. It can detect photons at ultra low light level such as single photon counting level. One of the most important characteristics of the PMT is the quantum efficiency (QE) of the photocathode. Among various kinds of photocathodes, a bialkali photocathode is commonly used for particle physics experiments since it has higher sensitivity and lower dark current than other photocathodes. QE of the conventional bialkali photocathode is 27%.Since 2007, we have made a significant improvement in the QE of the bialkali photocathode, achieving as high as 43% at peak wavelength by precise control of the photocathode activation process. This photocathode was named ultra bialkali (UBA) and was incorporated into PMTs successfully.Additionally, we have developed another new kind of bialkali photocathode for very low-temperature environments. At −175°C, the new bialkali photocathode shows good cathode linearity up to 300nA, and it has 28% QE and lower dark current than the UBA photocathode. A PMT with the new photocathode is expected to be an ideal detector for Dark Matter experiments or double-beta decay.

Large Kerr nonlinearities on cavity-atom polaritons

I analyze a scheme that is capable of producing large Kerr nonlinearities on cavity-atom polaritons in a cavity quantum electrodynamics system consisting of multiple three-level atoms confined in a cavity mode. A weak control laser coupled to the atoms from free space induces destructive quantum interference in the polariton excitation of the coupled cavity-atom system and creates large Kerr nonlinearities on the intra-cavity light field. The scheme can be used for optical switching or cross-phase modulation of the cavity-atom polariton at ultralow light levels.

All-optical phase modulations in a silicon wire waveguide at ultralow light levels

Cross-phase modulation (XPM) in a silicon wire waveguide at 1.55 μm telecom band was studied down to ultralow light levels. In the low-power regime, we found that free-carrier dispersion as well as the optical Kerr effect contributes to the XPM. Possible mechanisms of the low-power XPM are discussed.

CMOS imaging for biomedical applications

CMOS photodetectors and imaging systems have shown that they possess adequate performance characteristics to replace CCDs or PMTs in some biomedical applications, thereby providing low power, portable, and cheap integrated bioimaging systems. Some advanced solutions, like novel active pixel sensors that detect ultra-low light levels, and avalanche photodiodes that are integrated in CMOS and perform single photon detection, are addressed in this paper.

A monolithic based NIRS front-end wireless sensor

This paper concerns a novel analog front-end of a wireless brain oxymeter smart sensoring instrument based on near-infrared spectroreflectometry (NIRS). The NIRS sensor makes use of dynamic threshold transistors (DTMOS) for low voltage (1V), low power and low noise enhancement. The design is composed of a transimpedance amplifier (TIA) and an operational transconductance amplifier (OTA). The OTA differential input pairs use DTMOS devices for input common mode range enhancement. The OTA was fabricated in a standard 0.18μm CMOS process technology. Measurements under a 5pF capacitive load for the OTA gave a DC open loop gain of 67dB, unity frequency gain bandwidth of 400kHz, input and output swings of 0.58 and 0.7V, a power consumption of 18μW, and an input referred noise of 134nV/√Hz at 1kHz without any extra noise reduction techniques. The achieved features of the proposed oxymeter front-end will allow ultra low-light level measurements, high resolution and good temperature stability.

All-optical switching at ultralow light levels

We report an experimental demonstration of all-optical switching at ultralow light levels in coherently prepared Rb atoms. A signal light pulse is switched on and off by a control light pulse at different frequencies in a four-level atomic system based on multiphoton interferences. We observed a switching efficiency of 55% with the signal and control light pulses containing approximately 20 photons each, corresponding to a control energy density of approximately 10(-5) photons per atomic cross section lambda(2)/(2pi).

Phase-controlled light switching at low light levels

We report experimental observations of interference between three-photon and one-photon excitations, and phase control of light attenuation and/or transmission in a four-level system. Either constructive or destructive interferences can be obtained by varying the phase and/or frequency of a weak control laser. The interference enables absorptive switching of one field by another field at different frequencies and ultralow light levels.

Oxidative stress in clinical situations - fact or fiction?

Oxidative stress in clinical situations - fact or fiction?

極微弱光イメージングとその生体計測への応用

極微弱光イメージングとその生体計測への応用

Image processing in video microscopy.

The technique called Video Microscopy has become very popular in the field of biomedical research, in such areas as the study of the behavior of calcium ion in single cells. The video microscopy utilizes advantages of both the light microscope and the video camera. There are two typical methods in video microscopy, one of them being Video Enhanced contrast microscopy (VEC) and the other, Video Intensified microscopy (VIM). The VEC technique is being used to visualize specimens far beneath the resolution limits of the optical microscope, such as the observation of moving particles along the single microtuble, the behavior of the microtubles in mitosis and the observation of colloidal gold (5nm in size) in the living cell. VIM technique is a useful and powerful method used to observe or quantitize features under limited light conditions such as fluorescence, bioluminescence and chemiluminescence. The typical application is to study the cytosolic free Ca concentrations in a living cell with a fluorescence microscope. Photon counting imaging (under the ultra-low light level, it had better count photons individually rather than measure the amplitude of the light) is finding applications in biological research to detect chemiluminescence and bioluminescence. This technique provides a means of directly visualizing gene expression in single cells, imaging metabolites in tumor tissue and visualizing the chemiluminescence associated with oxidative metabolism in phagocytic cells. It is clear that VEC and VIM techniques are very promising methods in biomedical research.

Progress in low-light-level charge-coupled device imaging in astronomy

Techniques for data acquisition and processing, which permit accurate photometry at a level of 10−4 of the background night-sky level, are described. High quantum efficiency, excellent linearity, and low noise make frame-transfer silicon charge-coupled devices (CCD’s) nearly ideal imagers at ultralow-light levels in the UV to 900-nm range. Scientific-grade CCD’s are now available with less than 10-electron noise from several manufacturers. In astronomy these CCD’s permit studies of objects that are 100 times fainter than is possible by using photographic or video-camera techniques. Detection levels of 2 × 10−5 photons m−2 nm−1 sec−1 pixel−1 have been achieved. The efficiency of telescopes of all apertures has increased to the point at which observations that were unthinkable a decade ago are now becoming routine. New techniques for ultradeep imaging with CCD’s are described. The telescope is moved randomly between exposures, producing 30–100 disregistered images. Automated image processing on a workstation yields the final image, corrected for CCD imperfections and sky + optics systematics. Faint galaxies and stars of 30th magnitude are detected in 10-h integration on a 4-m telescope, corresponding to 0.02 photon sec−1 pixel−1. These techniques may be applied to longer-wavelength imagers with similar problems of bad pixels, bad lines or columns, background variations, etc. Application to faint-galaxy photometry is reviewed, and mosaic CCD imagers are discussed.

Operation and properties of a p-n avalanche photodiode in a charge integrating mode

An experimental study of charge storage operation in a Si p-n avalanche photodiode (APD) is discussed. It is shown that when the APD is pulsed beyond the breakdown voltage, avalanche multiplication gains of more than 10/sup 5/ are possible and the count rate of photoinduced output events is proportional to the input light intensity at ultralow-light levels. Moreover, in the below-breakdown mode, the amount of output signal charge is proportional to the input light intensity, while the gains are restricted to several tens and below. The slope of photoelectric conversion curves approaches gamma equivalent to 0.5, as a result of self-quenching of the avalanche discharge. >