Microchannel Plate Stack Research Articles

Continuous temporal ion detection combined with time-gated imaging: Normalization over a large dynamic range

Imaging micro-channel plate (MCP) detectors are a common tool for chemical physics studies used to image a single ion mass species in a time-of-flight (TOF) spectrum. Temporal selection of the mass to be imaged is traditionally implemented by gating the voltage across the MCP stack, however this leads to the loss of all information about other species in the mass spectrum. Here we show that by gating the phosphor voltage instead, as has been demonstrated by Zajfman et al. (1995) among others, we gain the capability of measuring multiple masses in TOF while retaining the ability to image a single desired species. In our precision spectroscopy experiment, we image the spatial distribution of Hf+ photodissociation fragments, while its more plentiful HfF+ precursor, which arrives at a later time, can also be detected in TOF. This enables the shot by shot normalization of technical noise associated with the precursor production. Since the scheme alters only the configuration of the high-voltage switch, it can be readily implemented in most existing gated MCP setups, allowing the full TOF information to be harvested. Combining the imaging and TOF data in a single shot, we can detect species with substantially different abundances.

使用曲面微通道板和感应电荷位置灵敏阳极的软X射线-极紫外光子计数成像探测器研究

The research on key techniques of wide field extreme ultraviolet( EUV) spherical micro-channel plate( MCP) photon-counting imaging detector which will be used in space probe in China have been done.Firstly,the secondary electron yield model of photocathode material was built,and the secondary yield of alkali halide and MCP in soft X-ray and EUV band were calculated using the model. The measurement equipment of MCP's quantum detection efficiency also was set up. The calculated fomula of MCP' s quantum efficiency was introduced,and MCP's quantum efficiency vs. wavelength and incidence angle in soft X-ray and EUV region were measured. secondly,the instrument of solid core spherical MCP fabrication was established,a set ofspherical MCP with 150 mm radius were made using the instrument. The 48 mm induced charge wedge and strip anode in effective diameter was made by the use of traditional UV lithography,and the photon-counting imaging detector was integrated based on the anode and spherical MCP stack in Z configuration. Thirdly,the position readout electronics including analog frent-end and digital processing circuit and the software with image distortion rectification and real-time collection were developed. Finally,the measurement instrument of spherical MCP detector's spatial resolution and image linearity was built,and the specifications of the detector were measured using the instrument,showing that all technical specificaions of the detector satisfy the design requirements.

Multi-channel picosecond photon timing with microchannel plate detectors

Microchannel plate-based detectors have the capability to photon-count at time resolutions which outperform solid-state devices such as the APD or SiPM, and have a geometry that lends itself to pixelated readouts. We describe a multi-channel, photon-counting microchannel plate detector optimised for photon timing in the picosecond regime. The detector was originally developed for application to time-resolved spectroscopy in the life sciences, however its performance characteristics make it suitable for applications where high time resolution and multi-channel photon-counting are required including Cherenkov light detection in nuclear physics, particle physics, and astroparticle astronomy. We describe the prototype detector, a sealed tube device comprising an optical photocathode proximity focussed to a small pore microchannel plate stack. Event charge is collected on a multi-channel readout comprising an 8×8 pixel array, manufactured on a multilayer ceramic, which provides vacuum integrity for the detector enclosure and a multi-way electrical feedthrough for the readout array. Each pixel addresses one channel of a NINO ASIC, a multi-channel preamplifier–discriminator device. The discriminator outputs are timed to 25 ps by the HPTDC time-to-digital converter ASIC, which uses a time-over-threshold technique for amplitude walk correction. We present performance measurements using a pulsed laser of the 64 channel prototype system comprising a 25 mm detector, NINO front-end, and a CAEN V1290A VME module utilising HPTDC. We discuss the next phase in the project—design and manufacture of a 40 mm detector with a 16×16 pixel 2 readout coupled to custom NINO/HPTDC electronics constructed as a series of 64 channel modules, expandable to even larger channel densities.

Fast, High Resolution Mass Spectrometry Imaging Using a Medipix Pixelated Detector

In mass spectrometry imaging, spatial resolution is pushed to its limits with the use of ion microscope mass spectrometric imaging systems. An ion microscope magnifies and then projects the original spatial distribution of ions from a sample surface onto a position-sensitive detector, while retaining time-of-flight mass separation capabilities. Here, a new type of position-sensitive detector based on a chevron microchannel plate stack in combination with a 512 × 512 complementary metal-oxide-semiconductor based pixel detector is coupled to an ion microscope. Spatial resolving power better than 6 μm is demonstrated by secondary ion mass spectrometry and 8-10 μm spatial resolving power is achieved with laser desorption ionization. A detailed evaluation of key performance criteria such as spatial resolution, acquisition speed, and data handling is presented.

High-resolution UV, alpha and neutron imaging with the Timepix CMOS readout

A CMOS application-specific integrated circuit (ASIC) called the “Timepix” has been used to readout the pulsed charge signal from various microchannel plate (MCP) stacks. The Timepix 256×256 array is a newer version of the Medipix2 ASIC with added features and modes. One of these modes is the “time over threshold” (TOT) mode where the amplitude of a single charge event can be determined per pixel. With a properly sized input charge cloud from an MCP stack, the centroid of the charge cloud can be determined to sub-pixel accuracy, allowing much higher spatial resolution than the 55 μm pixel size. Using this technique, we demonstrate a spatial resolution better than 57 lp/mm for UV photons, limited by the MCP pore spacing. Also, by changing the top MCP in the stack to a neutron-sensitive MCP, we show a spatial resolution to thermal neutrons of less than 35 μm FWHM. This technique can also be applied to alpha particle imaging using silicon diode arrays bump bonded to a Timepix. Allowing the large conversion charge generated by the alpha particle to diffuse over many pixels, we can centroid 5.5 MeV alphas from 241Am to 18 μm FWHM.

A time-of-flight spectrometer for angle-resolved detection of low energy electrons in two dimensions

We have developed a time-of-flight photoelectron spectrometer that simultaneously analyzes low energy electrons photoemitted from solid surfaces in an energy- and angle-resolved manner. To achieve this, a field free drift tube with an acceptance angle of 22° is combined with two-dimensional position-sensitive detection of photoelectrons, which is realized by a microchannel plate stack and a delay-line anode for position encoding. Here, we present the design considerations and principles of operation including analysis of multiple events per light pulse. The performance of the spectrometer is demonstrated by photoemission from a Cu(111) single crystalline surface by UV femtosecond laser pulses at 6.2 eV photon energy.

Multidetection (e,2e) electron spectrometer

An electron-pair coincidence spectrometer, using only a single electrostatic toroidal analyzer, has been developed for the study of final-state electron pairs following ionization by electron impact. The system allows the angular and energy distribution of electron pairs emitted in a selected plane to be detected by a single planar microchannel plate stack followed by two position-sensitive semicircular wedge-and-strip anodes. The output signals are decoded into energy, angle and nanosecond coincidence timing information from which relative energy and angular triple differential ionization cross sections are determined. The performance of the instrument is indicated by He I photoionization of krypton and the first measurements of differential cross sections for electron-impact ionization of the P3∕22 and P1∕22 states of krypton. For perpendicular-plane scattering and an excess energy of 10 eV for the P3∕22 state and 0.67 eV less for the P1∕22 state, these cross sections are significantly different for the two states and indicate the importance of the final state of the ion in the scattering process.

Cross-strip readouts for photon counting detectors with high spatial and temporal resolution

The combination of a photocathode, microchannel plate stack and photon counting, imaging readout provides a powerful tool for high dynamic range, high spatial resolution, and high timing accuracy detectors for the X-ray to visible light spectral range. Significant improvements in spatial resolution, quantum efficiency, and background rate have made these devices attractive for many applications and are being applied to completely new research areas. We describe the latest developments in high-resolution cross-strip (XS) anode readout for photon counting imaging with microchannel plates (MCPs). We show that the spatial resolution of an MCP detector with the cross-strip readout is now limited only by the MCP pore width. For the first time, we show images of resolution test masks illustrating the exceptional spatial resolution of the cross-strip readout, which at the present time can resolve features on the scale of /spl sim/7 /spl mu/m with MCP gains as low as 6/spl times/10/sup 5/. Low-gain operation of the detector with high spatial resolution shown in this paper is very beneficial for applications with high local counting rate and long lifetime requirements. The spatial resolution of the XS anode can be increased even further with improved anode uniformity, lower noise front-end electronics, and new centroiding algorithms. This could be important when MCPs with smaller than existing 6 /spl mu/m pores become commercially available, thus improving the detector resolution down to the few micrometer scale.

The formation of fluorescent and metastable fragments by photoexcitation of somediatomic molecules in the vacuum ultraviolet region

The formation of fluorescent and metastable fragments from four diatomic molecules,i.e. O2, N2, NO and CO, has been investigated in the vacuum ultraviolet region. The neutralparticles are detected by using a microchannel plate stack, where retardingelectric potentials prevent charged particles from reaching the detector. Everydiatomic molecule investigated here shows the formation of fluorescent andmetastable fragments in particular photon energy regions. Three Rydberg states ofO2 convergingto O2+(a 4Πu) undergo both neutral dissociation processes forming fluorescent[O+(4S)]3s 3S1 andmetastable [O+(4S)]3s 5S2; the yield curve for each fragment is determined. Direct and cascade formation of the fluorescent[N+(3P)]3s 4P fragmentfrom N2 are separated, and it is found that the dissociation of the4s σ Rydberg state convergingto N2+(C 2Σu+) preferentiallyproduces [N+(3P)]3p fragments,but not or weakly the [N+(3P)]3s 4P fragment. High -n Rydbergstates converging to NO+(c 3Π) and CO+(D 2Π) undergo neutral dissociation described by the core ion model, resulting in large peaks forneutral particle formation.

Competition between autoionization and dissociation in the[O2+(B 2Σg−)]nl and[O2+(c 4Σu−)]nl Rydberg states investigated by photon-induced dissociation to neutral fragments

Formation of fluorescing and metastable fragments from photon-induced dissociation ofO2 has been investigated in the 20.2–21.2 eV and 22.5–25.0 eV photon energy regions underhigh resolution. The neutral particles are detected using a microchannel plate stack, whereelectric potentials prevent charged particles from reaching the detector. Yieldcurves of excited neutral particles exhibit peaks at Rydberg states converging toO2+(B 2Σg−) andO2+(c 4Σu−).Furthermore, these yields are strongly enhanced athigh-n,enabling the measurement of their energy location and width. Asimple model for the decay of the Rydberg states converging toO2+(c 4Σu−) based on the competition between autoionization and neutral dissociation is used todescribe qualitatively the observed spectrum. The results indicate that the lifetime of theO2+(c 4Σu−)v = 0 level is two orders of magnitude longer than that of theO2+(c 4Σu−)v = 1 level.

A position sensitive detector for SPIDR—a mission to map the cosmic web

The primary goal of the Spectroscopy and Photometry of the IGM's Diffuse Radiation (SPIDR) mission is to detect and map the huge filamentary structures, the “cosmic web”, predicted to be present in the IGM. To accomplish this task the SPIDR instrument comprises six imaging spectrographs providing high-resolution spatial maps of IGM features in the critical OVI and CIV lines at both rest and red-shifted wavelengths. Each spectrograph uses a two-dimensional position sensitive microchannel plate detector to image UV dispersed by a normal incidence grating, encoding spectral and spatial information. Two-dimensional imaging is recovered by tomographic reconstruction of data from the slowly spinning spacecraft. The detector configuration utilizes an open faced microchannel plate stack coated with a UV photocathode. The conservative imaging requirements are met by a wedge and strip anode whose performance has been enhanced by using the image charge technique. Image charge provides a highly stable and predictable detector response which has enabled us to use software simulation to improve the linearity of the readout considerably.

Algorithms for correcting geometric distortions in delay-line anodes

Time-delay anodes are typically used in conjunction with microchannel plates to create photon counting, two-dimensional imaging detectors. The anode and associated electronics are used to compute the centroid of the charge cloud from the microchannel plate stack. The computation of event position is done in analog circuitry and then digitized to an appropriate number of bits. The analog nature of the time-delay anode makes it susceptible to a wide variety of outside influences resulting in variations in the correlation between physical space and the reported digital value. These variations, both local and global, must be corrected as part of the reduction of scientific data. If left uncorrected in spectral data, for example, these variations result in decreased spectral resolution, inaccurate wavelength identifications, and/or distorted spectral line profiles. This work presents successful algorithms for correcting the dominant distortions present in a time-delay anode. These algorithms were developed as part of the data reduction pipeline for the cosmic origins spectrograph (COS) far ultraviolet channel. COS is a fourth generation instrument for the Hubble Space Telescope.

Results of in-beam tests of an MCP-based vacuum sector prototype of the T0/centrality detector for ALICE

We report on results of efficiency tests for MIPs and timing resolution studies obtained with different layouts of micro-channel plate (MCP) detector prototypes at CERN PS test beams. The detector is composed of an MCP stack and multipad readout anodes integrated with a passive isochronal summator. Several types of setups were tested, including MCPs with different gain. Also, a very first test of the Micro Sphere Plates detector was performed. The performance of fast electronics including Double Threshold Discriminators and a fast multiplicity discriminator for short 2 ns signals was studied. Currently, the best experimental results for MCP detectors show 75 ps timing resolution obtained at 75% efficiency for the registration of a single muon. We expect further enhancements, mostly through improvements in the fast electronics.

Spatial distribution of electron cloud footprints from microchannel plates: Measurements and modeling

The measurements of the electron cloud footprints produced by a stack of microchannel plates (MCPs) as a function of gain, MCP-to-readout distance and accelerating electric field are presented. To investigate the charge footprint variation, we introduce a ballistic model of the charge cloud propagation based on the energy and angular distribution at the MCP output. We also simulate the Coulomb repulsion in the electron cloud, which is likely to cause the experimentally observed increase in the cloud size with increasing MCP gain. Calculation results for both models are compared to the charge footprint sizes measured both in our experiments with high rear-field values (∼200–900 V/mm) and in the experiments of Edgar et al. [Rev. Sci. Instrum. 60, 3673 (1989)] (accelerating electric field ∼30–130 V/mm).

Efficient and robust anion source, based on a microchannel plate electron source

In this work, an efficient, cheap, and robust anion source is described, which is based on a high-pressure supersonic expansion crossed with a pulsed high-energy electron beam. The special property of this anion source is “soft” electron attachment and efficient stabilization and cooling, which results predominantly in molecular and cluster anions of intact molecules. As electron source, a stack of microchannel plates is used, which is seeded by photoelectrons generated by a weak ultraviolet light pulse. By this special electron source 109–1010 electrons of 1 keV energy are provided at a pulse width of 150 ns. These operational conditions can be maintained up to a repetition rate of 4 kHz. Further advantages of this device are its long lifetime even at relatively high vacuum pressures and its stability against reactive samples, such as oxygen and organic molecules.

A novel imaging readout with improved speed and resolution

We describe a novel, charge centroiding, position readout, the spiral anode (SPAN) which combines excellent spatial resolution with very high count rate performance. SPAN is a planar structure of six electrically isolated electrodes. The ratio of the charges collected by the electrodes determines a two-dimensional position. The novel design allows the spatial resolution to be an order of magnitude better than the charge measurement accuracy. We present results from a prototype detector consisting of a microchannel plate stack in conjunction with the SPAN readout and discuss opportunities for the use of the SPAN readout with other photon counting detectors.

Investigations of the small-scale flat field response of microchannel plate detectors in the far and extreme ultraviolet

High signal-to-noise flat field images taken in the extreme and far ultraviolet with photon-counting microchannel plate (MCP) detectors are presented. Small spatial scale (<1 mm) modulations of the flat field, in particular the hexagonal mesh pattern and dead spots, are discussed. It is shown that the hexagonal modulation at the multifiber bundle boundaries of the MCPs is due to a differential nonlinearity in the mapping of input photon position to readout pixel and is caused by the rear plates of the MCP stack. Possible mechanisms for the nonlinearity, including hexagonal gain variations, are presented.

An x-ray image intensifier system for precision wavelength dispersive x-ray spectroscopy

We have constructed a high-resolution x-ray image intensifier (XRII) for use in atomic physics. The XRII consists of an alkali halide scintillator crystal coupled by a fiber optic to a proximity focused microchannel plate stack with a bialkali photocathode and wedge and strip readout. The useful area of the detector is 12 cm2. We have measured full width half maximum spatial resolutions at 22 keV of 300 μm and at 122 keV of 600 μm with 0.5-mm-thick and 1.6-mm-thick CsI(Na) crystals, respectively. With NaI(Tl) crystals, x-ray arrival times can be determined with sub-100 ns resolution. In this paper we present the detailed performance of the XRII as well as a brief discussion of the theory of photoelectron limited fast timing.

Optical Ranicon detectors for photon counting imaging. I

We discuss the design and development of Ranicon detectors for optical photon counting imaging on ground-based telescopes. The significant factors which determine the performance of these detectors are found to be the proximity focusing stage, the microchannel-plate stack (MCP), and the signal processing electronics. For applications in optical astronomy, the low photon counting efficiency typically found with optical MCP-based detectors, due to ion barrier films, presents an additional consideration. We review the performance of each stage of the Ranicon detector and the techniques for achieving optimal performance. A new approach to the signal processing electronics reduces nonlinearity, while achieving increased processing speeds and a position error corresponding to &amp;lt;21 μm FWHM. A significant improvement in detector performance is achieved with an advanced Ranicon incorporating a reduced proximity focusing gap and an unfilmed input plate in the MCP stack. The theoretical spatial resolution of both standard and advanced Ranicon designs is derived and compared to the experimentally determined values. For the advanced Ranicon, this spatial resolution is shown to be typically 40 μm FWHM at ∼650 nm. The point spread function of the Ranicon system is shown to be stationary over the active imaging area, principally due to the removal of nonlinearities and noise sources from the signal processing electronics.

A magnetic sector atom-probe FIM

The 60 ° magnetic sector atom-probe field ion microscope displays a section of the momentum spectrum on a stack of microchannel plates and a proximity-focused phosphor screen. A mass resolution ΔM / M ∼ 1/2000 is achieved, and “spectral lines” made up of a few individual ions may be used for the detection and identification of products of field evaporation of metals and their compounds with adsorbate gases. The capability of the new instrument is complementary to the established ToF atom probe as it employs very low evaporation rates in slow pulse or dc field evaporation, and displays the energy distribution of field ions. As an example of the difference, a palladium–neon ion compound PdNe+ is demonstrated to be very abundant, while it is a rare species in the ToF atom probe.