Microchannel plate based detectors are widely used for photon counting spectroscopy and imaging in astronomical, high energy physics and remote sensing applications1-15. We present progress in the development of imaging cross strip readout detectors using novel microchannel plates functionalized by atomic layer deposition (ALD). ALD microchannel plates have established formats of 10 cm with 10 μm pore sizes and 20 cm with 20 μm pores. ALD MCPs show with high quantum efficiency (>50% @115 nm) using opaque alkali halide photocathodes and very low background levels (0.05 events cm-2) have been achieved. Readout systems have also evolved and now cross-strip anodes and encoding electronics enable high spatial resolution (<20 μm) at low gain (106) and over large formats (10 cm) with high dynamic range (>5 MHz). These characteristics are essential for UV instrument concepts currently under study for NASA including the Large UV/Optical/IR Surveyor (LUVOIR)16, the Habitable Exoplanet Imaging Mission (HABEX)16, and Cosmic Evolution Through UV Spectroscopy (CETUS)16.
We report on life testing of conventional microchannel plates (MCPs) and atomic layer deposition (ALD) MCPs. For the Global-scale Observations of the Limb and Disk (GOLD) mission, long-duration, deep charge extraction testing was performed on a Z-stack triplet of 12 μm pore conventional MCPs with a CsI photocathode on the top surface. A relatively low gain (≈1000e-), modest charge extraction (0.07 C/cm2) full-field conditioning burn-in was performed followed by a very deep narrow line burn-in to emulate a GOLD spectral line. The gain local to the line burn-in decreased by ≈20% over ≈1 C/cm2 of extracted charge, and then remained stable (to 95 C/cm2). We also present the performance of several sets of 20 μm pore ALD MCPs with MgO secondary electron emission layers through full-field conditioning burn-ins at both full gain and low gain.
We present recent progress in the development of novel microchannel plates (MCPs) manufactured using standard lead glass and with borosilicate glass microcapillary arrays functionalized using Atomic Layer Deposition (ALD) technology. Standard glass MCPs have achieved high quantum efficiency (~60% @115 nm & 65 nm) using opaque alkali halide photocathodes. Enhanced performance standard glass MCPs have also been demonstrated with no fixed pattern noise due to construction defects. Novel borosilicate glass atomic layer deposited MCPs up to 20 cm format show good overall response uniformity, tight pulse height distributions and very low background levels (0.05 events cm-2). Spatial resolutions of the order of 20 μm are demonstrated with 10 μm pore atomic layer deposited MCPs, and their fixed pattern noise has been significantly reduced. Bialkali cathodes in sealed tubes show high (<30%) efficiency at ~200 nm and long wavelength cutoffs at ~360 nm have been engineered.
Microchannel plate sensors are widely used as photon counting imagers in many applications, including, astronomy, high energy physics, and remote sensing. Potential future NASA observatories with ultraviolet instruments, such as LUVOIR and HABEX, will require large area detectors (8k × 8k pixels) with large dynamic range (≥1 kHz/resel), high quantum efficiency (75% peak), and very low backgrounds (≤0.1 cts/sec/cm2 ). New microchannel plate technology combining borosilicate glass microcapillary arrays with high efficiency materials applied by atomic layer deposition are being developed with these goals in mind. Detectors with these microchannel plates can be made in large formats (up to 400 cm2 ) with focal plane matching, have high spatial resolution (<20μm), are radiation hard, and have very low background rates (<0.05 events/sec/cm2 ) with no readout noise. Typical sensors make use of high efficiency photocathodes in open faced detectors (< 110 nm range) or in ultra-high vacuum sealed tube devices (>110 nm range). New photocathodes, such as GaN and hybrid bialkali/alkali halide, have high quantum efficiencies over broadband wavelengths. Cross-strip anodes are well suited for large format detectors with high spatial resolution and high dynamic range requirements. Improvements to detector anodes and readout electronics have resulted in better spatial resolution (10×), output event rate (100×), and temporal resolution (1000×), all the while operating at lower gain (10×). Combining these developments can have a significant impact to potential future NASA sub-orbital and satellite instruments.
The Emirates Mars Mission (EMM) UV Spectrograph (EMUS) is a far ultraviolet (102 nm to 170 nm) imaging spectrograph for characterization of the Martian exosphere and thermosphere. Imaging is accomplished by a photon counting open-face microchannel plate (MCP) detector using a cross delay line (XDL) readout. An MCP gain stabilization (“scrub”) followed by lifetime spectral line burn-in simulation has been completed on a bare MCP detector at SSL. Gain and sensitivity stability of better than 7% has been demonstrated for total dose of 2.5 × 1012 photons cm−2 (2 C · cm−2 ) at 5.5 kHz mm−2 counting rates, validating the efficacy of an initial low gain full-field scrub.
The GOLD mission is a NASA Explorer class ultraviolet Earth observing spectroscopy instrument that will be flown on a telecommunications satellite in geostationary orbit in 2018. Microchannel plate detectors operating in the 132 nm to 162 nm FUV bandpass with 2D imaging cross delay line readouts and electronics have been built for each of the two spectrometer channels for GOLD. The detectors are “open face” with CsI photocathodes, providing ~30% efficiency at 130.4 nm and ~15% efficiency at 160.8 nm. These detectors with their position encoding electronics provide ~600 x 500 FWHM resolution elements and are photon counting, with event handling rates of > 200 KHz. The operational details of the detectors and their performance are discussed.
The ICON Far Ultra Violet Imaging Spectrograph (ICON FUV) instrument includes one sealed tube microchannel plate (MCP) converter for each of two (135.6 nm and 157 nm wavelength) channels. These are each integrated with a CCD camera assembly to provide ICON FUV’s sensor systems. The ICON FUV sealed tube converters have a 27mm active area and include a double MCP stack with a cesium iodide (CsI) photocathode, a magnesium fluoride (MgF2) input window, a ceramic and Kovar brazed mechanical structure and a phosphor output screen. Performance characteristics are measured for each detector throughout manufacturing and before shipping and include the collection of gain-voltage data, pulse height distributions, flat field images of the output window, background count rates and images, quantum efficiency curves and resolution characteristics. The design and testing of the ICON FUV sealed tube converters are described here.