Photon Sensitivity Research Articles

Characterisation of a new generation of VUV low-light sensors

Silicon Photo-Multipliers (SiPMs) have emerged as a compelling photo-sensor solution over the course of the last decade. In contrast to the widely used Photomultiplier Tubes (PMTs), SiPMs are low-voltage powered, optimal for operation at cryogenic temperatures, and have low radioactivity lev- els with high gain stability over the time in operational conditions. For these reasons, large-scale low-background cryogenic experiments, such as the next- generation Enriched Xenon Observatory experiment (nEXO), are migrating to a SiPM-based light detection system. In this paper we report on the charac- terization of the Hamamatsu VUV4 (S/N: S13370-6152) Vacuum Ultra-Violet (VUV) sensitive Multi-Pixel Photon Counters (MPPC)s as part of the develop- ment of a solution for the detection of liquid xenon scintillation light for the nEXO experiment.

Modeling Gain Mechanisms in Amorphous Silicon Due to Efficient Carrier Multiplication and Trap-Induced Junction Modulation

Amorphous materials have low mobility due to their nature of disorder. Surprisingly, some disordered materials showed photocurrent amplification not by conventional photoconductive gain. Recently, amorphous Silicon (a-Si) photodiodes with thin a-Si layer (∼40 nm) have shown a gain-bandwidth product of over 2 THz with very low excess noise and also have been used as a gain media in a cascaded system with single photon sensitivity. To unveil the true gain mechanism, we performed theoretical modeling and numerical analysis along with experimental data at different frequencies. We show evidence of highly effective carrier multiplication process within a-Si as the primary gain mechanism, especially at high frequency. We also show presence of trap-induced junction modulation at much lower frequency. We modeled the gain mechanism in a-Si by solving the transport equations including dynamics of defect states and carrier multiplication via the local field model. We further justified the application of local field model for thin a-Si, based on the property that in a-Si, the mean-free path for energy relaxation is orders of magnitude greater than the mean-free-path for momentum relaxation. The analysis further suggests that the carrier multiplication process in thin a-Si can be much more efficient than in thick a-Si, even stronger than single crystalline Si in some cases. Although seemingly counter intuitive, this is consistent with the proposed cycling excitation process where the localized states in the bandtails of disordered materials such as a-Si relax the k -selection rule and increase the rate of carrier multiplication.

A quantitative approach to select PMTs for large detectors

Photomultiplier tubes (PMTs) are widely used in neutrino and other experiments for the detection of weak light. To date PMTs are the most sensitive single photon detector per unit area. In addition to the quantum efficiency for photon detection, there are a number of other specifications, such as rate and amplitude of after-pulses, dark noise rate, transit time spread, radioactive background of glass, peak-to-valley ratio, etc. All affect the photon detection and hence the physics goals. In addition, cost is another major factor for large experiments. It is important to know how to properly take into account all these parameters and choose the most appropriate PMTs. In this paper, we present an approach to quantify the impact of all parameters on the physics goals, including cost and risk. This method has been successfully used in the JUNO experiment. It can be applied to other experiments with large number of PMTs.

Material Imaging Via X-RAY Emitted from laser produced plasma

The present work represented to the new idea techinque of imaging material through X-ray emitted from laser produced plasma, here, the plasma intensity in uv-visible region spectrum was measurment from the interaction of the 1.06μm of nedumium-glass laser pulse duration of energy 4J, with five target laser: Al, Cu, C, Pb and Stainless Steel(St.St). Astudy of the X-ray emission intensity as a function of laser produced plasma density and surrouding pressure has been a complished using a high sensitive photon detection and counting technique assoicated with an X-ray intensifying screen whose function is based on X-ray florescence. the stainless –stell target was found to have the highest plasma emission intensity, and as a result it has higher X-ray emission intensity. the results show that the plasma X-ray emission intensity is increased with decreasing surrouding pressure, while this emission intensity is increased with increasing the laser power density. In order to study the spatial scanning of transmitted plasma X-ray intensity and study the factors affecting the x-ray imaging process, a special designed Cu specimen of varying thickness was used. The spatial scanning of transmitted x-ray emission intensity shows a comparative picture to the Cu specimen from the recorded x-ray intensity, in which it decreases at thicker region acorrding to lamberts absorbtion law.

Robustness of Clonogenic Assays as a Biomarker for Cancer Cell Radiosensitivity.

Photon radiation therapy is a major curative treatment for cancer. However, the lack of robust predictive biomarkers for radiosensitivity precludes personalized radiation therapy. Clonogenic assays are the gold standard method for measuring the radiosensitivity of cancer cells. Although a large number of publications describe the use of clonogenic assays to measure cancer cell radiosensitivity, the robustness of results from different studies is unclear. To address this, we conducted a comprehensive detailed literature search of 256 common cancer cell lines and identified the eight cell lines most-frequently examined for photon sensitivity using clonogenic assays. Survival endpoints and experimental parameters from all 620 relevant experiments were compiled and analyzed. We found that the coefficients of variation for SF2 (surviving fraction after 2 Gy irradiation) and for D10 (dose that yields a surviving fraction of 10%) were below 30% for all cell lines, indicating that SF2 and D10 have acceptable inter-assay precision. These data support further analysis of published data on clonogenic assays using SF2 and D10 as survival endpoints, which facilitates robust identification of biological profiles representative of cancer cell sensitivity to photons.

Solid-State Detector SPECT Myocardial Perfusion Imaging.

There has been an evolutionary leap in SPECT imaging with the advent of camera systems that use solid-state crystals and novel collimator designs configured specifically for cardiac imaging. Solid-state SPECT camera systems have facilitated dramatic reductions in both imaging time and radiation dose while maintaining high diagnostic accuracy. These advances are related to simultaneous improvement in photon sensitivity due to the collimator and imaging geometry, as well as image resolution due to the improved energy resolution of the new crystals. Improved photon sensitivity has facilitated fast or low-dose myocardial perfusion imaging (MPI), and early dynamic imaging has emerged as a technique for assessing myocardial blood flow with SPECT. Lastly, general-purpose solid-state camera systems and hybrid SPECT/CT systems have also been developed that may have important clinical roles in cardiac imaging. This review summarizes state-of-the-art solid-state SPECT MPI technology and clinical applications, including emerging techniques for SPECT MPI flow estimation. We also discuss imaging protocols used with the new cameras, potential imaging pitfalls, and the latest data providing large-scale validation of the diagnostic and prognostic value of this new technology.

Development of broadband x-ray radiography for diagnosing magnetically driven cylindrically compressed matter

Experiments and modeling of x-ray radiography of millimeter diameter solid Al wires with laser-produced broadband x rays are reported. Experiments were performed using the 50-TW Leopard short-pulse laser in a laser and pulsed power chamber at the Nevada Terawatt Facility. To characterize broadband x rays and demonstrate a radiographic capability, bremsstrahlung, escaping electrons, and radiograph images of Al wires were simultaneously measured. The angularly resolved x-ray spectra are modeled by comparing measured bremsstrahlung signals in the range between 10 and ∼500 keV with hybrid particle-in-cell simulations. Transmission of Al wires from the radiograph images is further simulated with a Monte Carlo code. The measured transmission profiles of Al wires with three different diameters agree with calculations when a simulated x-ray spectrum composed of line emissions and bremsstrahlung is used with a source size of 600 ± 200 μm. Transmission calculations with only 22 keV Ag Kα or an exponential x-ray spectrum do not reproduce the measurement, suggesting that the accurate determination of an x-ray source spectrum, as well as the inclusion of the photon sensitivity of the detector, is critical in transmission calculations to infer the density of an object. The laser-based broadband x-ray radiography that was developed has been successfully implemented in a pulsed power chamber for future laser-pulsed-power coupled experiments.

Multi-wavelength spatial frequency domain diffuse optical tomography using single-pixel imaging based on lock-in photon counting.

We present a spatial frequency domain (SFD) diffuse optical tomography for simultaneous acquisition of multi-wavelength tomographic images of turbid media. We propose a highly sensitive single-pixel SFD imaging system for simultaneously collecting multi-wavelength spatially modulated reflectance images, instead of using the expensive electron-multiplying charge-coupled device camera that requires switching between the multi-wavelength collections. The single-pixel SFD imaging system using three low-power light sources (455, 532 and 660 nm) that were intensity-modulated by square waves with three different frequencies for frequency encoding, and all the light sources were focused onto one digital micromirror device (DMD) for generating wide-field sinusoidal illumination patterns. Reflected light from the surface of the turbid media was modulated by the other DMD with many sampling patterns before being spatially integrated. Spatially integrated light signals were frequency decoded with a novel highly sensitive lock-in photon counting detection, then multi-wavelength spatially modulated reflectance images were recovered with the single-pixel imaging (SPI) method. We incorporated the two-dimensional discrete cosine transform (DCT) into the SPI method to reduce the number of sampling patterns, and, thereby, the proposed DCT-SPI scheme achieved a fast acquisition of SFD reflectance images that is desired for a dynamic SFD imaging application. Direct current (DC) and alternating current (AC) amplitudes at all the locations on the media surface were extracted from the recovered images. Multi-wavelength tomographic images were reconstructed with an inversion algorithm based on the first-order Rytov approximation of the diffusion equation, using both the extracted DC and AC amplitudes. We performed experiments using a series of tissue simulating phantoms to verify the performances of the proposed approach and compared the experimental results with those using a conventional camera-based SFD imaging system. The results demonstrate that our DCT-SPI based SFD-DOT approach is well suited for simultaneous reconstruction of multi-wavelength tomographic images to pave the way for many SFD imaging applications.

Experimental characterization of SNSPD receiver technology for deep space FSO under laboratory testbed conditions

Deep space Free Space Optical (FSO) systems are an emerging technology, characterized with very high performance in terms of information capacity and communication distances. However, this novel technology demands preliminary experiments, which are unmanageable in real conditions. Regarding this issue, an innovative approach for testing deep space optical communication links in controlled laboratory environment is developed. The proposed testbed is based on fibre optics technology and combines a couple of units, which represent a real deep space FSO link. The parameters of several different photon-counting receivers are discussed. Similar to already demonstrated deep space missions, the implemented optical receiver is Superconducting Nanowire Single Photon Detector (SNSPD) characterized with high single photon sensitivity and detection efficiency. Consequently, in this paper an authentic deep space Poisson channel is theoretically defined, emulated and examined. The description of the Poisson point process is supported by real SNSPD measurements in terms of high efficiency single-photon detection. Moreover, a self-developed unit including Variable Optical Attenuator (VOA) and software controlling the attenuation in the communication loop of the breadboard is applied. Apart from possibility for representing atmospheric-induced fading due to turbulence and Mie scattering effects, the module is utilized as a precise attenuator changing dynamically the optical power based on lookup tables. Addressing the capabilities of VOA unit, detection intensity, detector noise and efficiency versus SNSPD’s bias current is measured. In addition, VOA is used as a very slow optical modulator for testing the restrictions regarding On-Off extinction ratio of the implemented SNSPD detector.

Megapixels @ Megahertz – The AGIPD high-speed cameras for the European XFEL

The European XFEL is an extremely brilliant Free Electron Laser Source with a very demanding pulse structure: trains of 2700 X-ray pulses are repeated at 10 Hz. The pulses inside the train are spaced by 220 ns and each one contains up to 1012 photons of 12.4 keV, while being ≤100fs in length. AGIPD, the Adaptive Gain Integrating Pixel Detector, is a hybrid pixel detector developed by DESY, PSI, and the Universities of Bonn and Hamburg to cope with these properties. It is a fast, low noise integrating detector, with single photon sensitivity (for Eγ⪆6keV) and a large dynamic range, up to 104 photons at 12.4 keV. This is achieved with a charge sensitive amplifier with 3 adaptively selected gains per pixel. 352 images can be recorded at up to 6.5 MHz and stored in the in-pixel analogue memory and read out between pulse trains. The core component of this detector is the AGIPD ASIC, which consists of 64 × 64 pixels of 200µm×200µm. Control of the ASIC’s image acquisition and analogue readout is via a command based interface. FPGA based electronic boards, controlling ASIC operation, image digitisation and 10 GE data transmission interface AGIPD detectors to DAQ and control systems. An AGIPD 1 Mpixel detector has been installed at the SPB 1 experimental station in August 2017, while a second one is currently commissioned for the MID 2 endstation. A larger (4 Mpixel) AGIPD detector and one to employ Hi-Z sensor material to efficiently register photons up to Eγ≈25keV are currently under construction.

Two-crossed-polarizers based optical property modulation method for ionizing radiation detection for positron emission tomography

Recent work shows that Pockels effect and optics pump-probe measurement could be utilized as a novel method for 511 keV ionizing radiation photon detection for positron emission tomography (PET) which could potentially overcome the inherent physical limitation for coincidence time resolution of around 100 ps (Tao et al 2016 Phys. Med. Biol. 61 7600–22). In this paper, we embrace this observation and introduce a two-crossed-polarizers based setup to achieve similar detection concept, which is a simpler and more compact setup with comparable ionizing radiation detection capability as the setup used in the previously proposed work. We evaluated the performance of our experimental setup with Lithium Niobate (LiNbO3) and Cadmium Telluride (CdTe) detector crystals, and the desired properties of an ideal detector crystal were discussed. The modulation signal induced by 511 keV photons in both LiNbO3 and CdTe can be detected with repeatable signal amplitude using two-crossed-polarizers based method, while CdTe could provide eight times higher detection sensitivity to 511 keV photons than LiNbO3 under the same bias voltage, suggesting high effective Z number and high density properties of CdTe, as well as a shorter carrier lifetime and lower carrier mobility of LiNbO3. In addition, the strength of modulation signal increased linearly with bias voltage before saturation. The modulation signal strength in LiNbO3 continued to increase after 2000 V due to its high resistivity which could reduce the dark current in the detector, while the modulation signal of CdTe with low resistivity tended to be saturated at a bias voltage higher than 1200 V. Therefore, further increasing the bias voltage for detector crystals (especially for LiNbO3) may enhance the modulation strength and improve the detection sensitivity for annihilation photons.

Wearable, Fiber-less, Multi-Channel System for Continuous Wave Functional Near Infrared Spectroscopy Based on Silicon Photomultipliers Detectors and Lock-In Amplification.

Development and in-vivo validation of a Continuous Wave (CW) functional Near Infrared Spectroscopy (fNIRS) system is presented. The system is wearable, fiber-less, multi-channel (16×16, 256 channels) and expandable and it relies on silicon photomultipliers (SiPMs) for light detection. SiPMs are inexpensive, low voltage and resilient semiconductor light detectors, whose performances are analogous to photomultiplier tubes (PMTs). The advantage of SiPMs with respect to PMTs is that they allow direct contact with the scalp and avoidance of optical fibers. In fact, the coupling of SiPMs and light emitting diodes (LEDs) allows the transfer of the analog signals to and from the scalp through thin electric cables that greatly increase the system flexibility. Moreover, the optical probes, mechanically resembling electroencephalographic electrodes, are robust against motion artifacts. In order to increase the signal-to-noise-ratio (SNR) of the fNIRS acquisition and to decrease ambient noise contamination, a digital lock-in technique was implemented through LEDs modulation and SiPMs signal processing chain. In-vivo validation proved the system capabilities of detecting functional brain activity in the sensorimotor cortices. When compared to other state-of-the-art wearable fNIRS systems, the single photon sensitivity and dynamic range of SiPMs can exploit the long and variable interoptode distances needed for estimation of brain functional hemodynamics using CW-fNIRS.

High Sensitivity Photon Sensors Relying on Superconducting Micro Resonators

High Sensitivity Photon Sensors Relying on Superconducting Micro Resonators

Demonstration of Microwave Multiplexed Readout of DC-Biased Superconducting Nanowire Detectors

Superconducting nanowires are widely used as sensitive single photon detectors with wide spectral coverage and high timing resolution. We describe a demonstration of an array of DC biased superconducting nanowire single photon detectors read out with a microwave multiplexing circuit. In this design, each individual nanowire is part of a resonant LC circuit where the inductance is dominated by the kinetic inductance of the nanowire. The circuit also contains two parallel plate capacitors, one of them is in parallel with the inductor and the other is coupled to a microwave transmission line which carries the signals to a cryogenic low noise amplifier. All of the nanowires are connected via resistors to a single DC bias line that enables the nanowires to be current biased close to their critical current. When a photon hits a nanowire it creates a normal hot spot which produces a voltage pulse across the LC circuit. This pulse rings down at the resonant frequency of the LC circuit over a time period that is fixed by the quality factor. We present measurements of an array of these devices and an evaluation of their performance in terms of frequency and time response.

Intercrystal scatter studies for a 1 mm3 resolution clinical PET system prototype

Positron emission tomography (PET) systems designed with multiplexed readout do not usually have the capability to resolve individual intercrystal scatter (ICS) interactions, leading to interaction mispositioning that degrades spatial resolution and contrast. A 3D position sensitive scintillation detector capable of individual ICS readout has been designed and incorporated into a 1 mm3 resolution clinical PET system used for locoregional imaging. Incorporating ICS events increases photon sensitivity by 51.5% compared to using only photoelectric events. A Compton scatter angle error minimization algorithm is used to estimate the first ICS interaction location for accurate line-of-response pairing of coincident photons. An optimal scatter angle error threshold of 15 degrees is used to discard ICS events with a high mismatch between energy-derived and position-derived intercrystal scatter angles. Finally, positioning rather than rejecting ICS events boosts peak contrast to noise ratio by 8.1%, and allows for an equivalent dose reduction of 12% while maintaining equivalent image quality.

Functionalized Carbon Nanotube Phototransistors with Sub-Femtowatt Sensitivity at Room Temperature

Detecting low intensity light requires photodetectors with high gain. Carbon nanotube (CNT) transistors functionalized with light absorbers have emerged as a promising approach to realize photodetectors that could approach single photon sensitivity at room temperature. Our previous work demonstrated high sensitivity for CNT transistors functionalized with C60, with modeling indicating that electron-donating sensitizers could lead to even better performance. Here we explore this concept and present a P3HT-functionalized CNT phototransistor capable of detecting 500 aW of visible light at room temperature, corresponding to a responsivity of 2e9 A/W (Gain > 4e9). Furthermore, the dynamical processes lead to a significantly improved response time down to the millisecond range. Combined, these factors suggest that functionalized quasi-one-dimensional channels are a promising path for next-generation room temperature photodetectors.

Selective-Assembling Hybrid Porphyrin-Silicon Nanowire Field-Effect Transistor (PSNFET) for Photonic Sensor

In this letter, a novel photonic sensor composed of a selective-assembling porphyrin-silicon nanowire field-effect transistor (PSNFET) was proposed and fabricated by the complimentary metal-oxide-semiconductor (CMOS)-compatible technique. By intensively designing the hydrophobic isolation structure in the novel device, selective assembling of a wealth of porphyrin molecules to the surface of the poly-Si nanowire can be achieved, which was verified by the laser confocal fluorescence microscopy, SEM, and AFM. Meanwhile, compared to the control group, the selective-assembling PSNFET shows improved sensitivity to porphyrin assembly itself as well as the photo-electronic detection. Such a device structure provides an innovative scheme for photonic sensitivity enhancement and the possibility for the hybrid sensor integration on silicon.

Particle identification with DIRCs at PANDA

The DIRC technology (Detection of Internally Reflected Cherenkov light) offers an excellent possibility to minimize the form factor of Cherenkov detectors in hermetic high energy detectors. The PANDA experiment at FAIR in Germany will combine a barrel-shaped DIRC with a disc-shaped DIRC to cover an angular range of 5 to 140 degrees. Particle identification for pions and kaons with a separation power of 3 standard deviations or more will be provided for momenta between 0.5 GeV/c and 3.5 GeV in the barrel region and up to 4 GeV/c in the forward region. Even though the concept is simple, the design and construction of a DIRC is challenging. High precision optics and mechanics are required to maintain the angular information of the Cherenkov photons during multiple internal reflections and to focus the individual photons onto position sensitive photon detectors. These sensors must combine high efficiencies for single photons with low dark count rates and good timing resolution at high rates. The choice of radiation hard fused silica for the optical material and of MCP-PMT photon sensors is essential for DIRC detectors to survive in an environment of radiation and strong magnetic field. The two DIRC detectors differ in the focusing optics, in the treatment of chromatic dispersion and in the electronic readout systems. The technical design of the two DIRC detectors and their validation by testing prototypes in a mixed particle beam at CERN are presented.

Hybridized MAPS with an in-pixel A-to-D conversion readout ASIC

Abstract New accelerator-based photon sources require pixel detectors with fast readout rate and large dynamic range. When the development is focused on detecting soft x-ray single photons then low noise is another competing requirement of the detector. FLORA, conceived to exploit the high repetition rate operation at LCLS-II with focus on soft X-rays, is being developed to address these needs. It targets single photon sensitivity at 250 eV, a dynamic range of 104 photons per pixel per frame, a continuous readout of more than 40k frames per second (kfps), and a pixel of 50 um × 50 um. We present and discuss technical choices and test results of the first prototypes.

Sensitive Time-Correlated Single Photon Counting Systems for Lumincescence Spectroscopy of Small Molecules and Building Blocks

Sensitive Time-Correlated Single Photon Counting Systems for Lumincescence Spectroscopy of Small Molecules and Building Blocks