Retroreflectors ('retros') in front of the receiver provide feedback from multiple locations of each heliostat's radiant footprint thereon, simultaneously for all of them. The retros and their mounts are made of quartz glass to allow placement in the 'hot zone'. To discriminate samples of light returned by multiple retros from each other and from the brightly lit receiver, the retro reflectivities are modulated at unique frequencies by spinning them. The presentation will show component and system test results.
A method is proposed to keep all heliostats in a Concentrated-Solar-Power (CSP) facility under closed-loop pointing control while also providing feedback on the detailed alignment of the segment mirrors of each heliostat. The method uses the sunlight reflected by the heliostats towards the receiver, and thus works under full operational conditions and without the need of secondary optical alignments. It is based on retro-reflectors (‘retros’) to simultaneously return samples of the sunlight reflected by each mirror back to that same mirror. It goes beyond previous efforts at using retros by placing them into the concentrated sunlight, instead of in its periphery. Quartz glass will be used for its heat tolerance, and reflectivity modulation for visibility is achieved by rotating the retros. The technology can be retrofitted into existing CSP facilities to improve operational efficiency, and it can be used to relax the stability requirements of heliostats, and thus their cost, in the planning of new ones.
We demonstrate high-energy x-ray (HEX-ray) generation using 3-mJ, 850fs pulses on a liquid metal target in a laser plasma x-ray Source (LPXS). The measured HEX-ray spectra reach into the MeV spectral range. The spectrum follows approximately a Boltzmann energy distribution with a maximum HEX-ray “temperature” of 350 to 440 keV. The low laser intensity requirement, orders of magnitude less than previously reported, enables operation with widely available picosecond, millijoule laser systems with hundreds of Watt average laser power. Based on lasers with Yb-doped active media, compact HEX-ray sources driven with kilowatt average laser power are achievable very soon.
We demonstrate High-Energy X-ray (HEX-ray) generation using 2.8-mJ, 850fs pulses on a liquid metal target in a Laser Plasma X-ray Source (LPXS). The measured HEX-ray spectra reach into the MeV spectral range. The spectra follow Boltzmann energy distributions with a maximum HEX-ray “temperature” of 420 keV. The low laser intensity requirement, orders of magnitude less than previously reported, enables operation with widely available picosecond, millijoule laser systems with hundreds of Watt average laser power. Based on lasers with Yb-doped active media, HEX-ray sources driven with kilowatt average laser power are achievable in the very near future.
A Laser-Driven Plasma X-ray Source (LPXS) can provide intense, hard X-rays in femtosecond pulses emitted from a micrometer-size spot on a recirculating liquid-metal target. Unlike X-ray tubes based on electron beams, which are subject to constraints of the electron optics and space-charge effects, there is no fundamental limit to the amount of laser power that can be concentrated into the micrometer focus. With the increasing availability of industrial picosecond and femtosecond laser systems it now is practical to offer high average X-ray flux, combined with far higher brilliance and far shorter pulses than possible with X-ray tubes. Because the laser target in an LPXS is a liquid-metal, each laser shot encounters a fresh surface. Metal vapor and droplets are collected and recirculated to the target metal pump for maintenance-free operation. Hard X-rays are generated at tens of keV photon energies consisting of continuum radiation and, depending on the target material composition, of Ga-K, Bi-K or In-K emission lines.
Incom Inc. is developing and commercializing a novel type of microchannel plate (MCP) electron multipliers. These new devices are called “ALD-GCA-MCPs” and are made from glass capillary arrays (GCA), glass plates with a regular array of hollow glass capillaries that are functionalized using atomic layer deposition (ALD) thin film coating technology. ALD-GCA-MCPs are a technology advancement that affords MCPs with significantly improved performance, as compared to conventional MCPs. Notable benefits over conventional lead-oxide based MCPs are larger size, high and stable gain, low dark counts and gamma-ray sensitivity, improved mechanical stability, and the unique ability to tune the MCP resistance and electron amplification characteristics over a much wider range and independent from the glass substrate. Incom now routinely produces ALD-GCA-MCPs with 10 and 20 μm pore size at MCP dimensions up to 20 cm x 20 cm. The MCPs show a number of favorable characteristics, such as 3x lower gamma-ray sensitivity compared to conventional MPCs, low background (< 0.05 cts/s/cm2), and stable, high gains (<1×104 for single MCP and <1×107 for a chevron pair configuration, at 1000V/MCP). ALD-GCA-MCPs find use in a variety of photon counting applications and are particularly suited for charged particle detection that requires high timing and spatial resolution, such as Ion time-of-flight (TOF), electron spectroscopies, analytical and space instruments, and MCP-based photomultipliers such as the Large-Area Picosecond Photodetector (LAPPDTM), which is also being developed by Incom Inc. In this paper, we provide a brief technology overview highlighting the current state of the art of Incom’s ALD-GCA-MCP technology, as well as current and future development efforts that address the GCA glass substrate as well as the resistive and electron emissive ALD coatings.
Incom, Inc. is now producing commercially available Large Area Picosecond Photo-Detectors (LAPPD™) usable in applications by early adopters. The first generation LAPPD™ is an all-glass 230 x 220 x 22 mm3 flat panel photodetector with a chevron stack of glass capillary array microchannel plates functionalized by atomic layer deposition, a semitransparent bi-alkali photocathode, and a strip-line anode. The photodetector is being optimized for applications requiring picosecond timing and millimeter spatial resolution and has achieved single photoelectron (PE) timing resolutions of α≤52 ps. Typical performance metrics include electron gains of 107 at 1 kV per MCP, low dark noise rates (15-30 Hz/cm2 at moderate gains), single PE spatial response along and across strips of 1.8 mm and 0.76 mm respectively and quantum efficiencies that are typically ≥20% at 365 nm. Changes to the “baseline” LAPPD™ are under development to optimize the photodetector for applications requiring very high spatial resolutions.
In proton therapy treatment, proton residual energy after transmission through the treatment target may be determined by measuring sub-relativistic transmitted proton time-of-flight velocity and hence the residual energy. We have begun developing this method by conducting proton beam tests using Large Area Picosecond Photon Detectors (LAPPDs) which we have been developing for High Energy and Nuclear Physics Applications. LAPPDs are 20cm x 20cm area Micro Channel Plate Photomultiplier Tubes (MCP-PMTs) with millimeter-scale spatial resolution, good quantum efficiency and outstanding timing resolution of ≤70 picoseconds rms for single photoelectrons. We have constructed a time-of-flight telescope using a pair of LAPPDs at 10 cm separation, and have carried out our first tests of this telescope at the Massachusetts General Hospital's Francis Burr Proton Therapy Center. Treatment protons are sub-relativistic, so precise timing resolution can be combined with paired imaging detectors in a compact configuration while still yielding high accuracy in proton residual energy measurements through proton velocity determination from nearly monoenergetic protons. This can be done either for proton bunches or for individual protons. Tests were performed both in "ionization mode" using only the Microchannel Plates to detect the proton bunch structure and also in "photodetection mode" using nanosecond-decay-time quenched plastic scintillators to excite the photocathode within each of the paired LAPPDs. Data acquisition was performed using a remotely operated oscilloscope in our first beam test, and using 5Gsps DRS4 Evaluation Board waveform digitizers in our second test, in each case reading out both ends of single microstrips from among the 30 within an LAPPD. First results for this method and future plans are presented.
We have demonstrated a high resolution (10 micron) X-ray scintillator plate as part of an indirect X-ray detection system. Scintillator plates are typically integrated with a 2-dimensional array of photodiodes based upon amorphous Si. This paper describes an alternative digital capture system that leverages low cost CCD/CMOS cameras. Our detector has a broad set of potential applications, however the initial target application is mammography. Full-field mammography mandates an imaging area of 180mm x 240mm or larger. Very large CCD/CMOS sensors have recently been developed for high resolution cameras, such as the 250-pixel Canon camera which has sensor dimensions of 202mm x 205mm, and could conceivably be matched to our high-resolution scintillator plate without any intervening optics for magnification. However, such large format CCD/CMOS sensors have limited availability because of low production yields and high cost considerations. On the other hand, small form (36mm x 24mm) and medium format (44mm x 33mm) CCD/CMOS-based photodiodes have become widely available at low cost due to their applications in the large markets of mobile devices and consumer cameras. We have therefore developed a simple optical scheme for utilizing four small or medium format CCD/CMOS cameras to capture a larger, high-resolution image. Current systems employed in screening mammography resolve tissue features of 75-100 microns. Suspicious features found during preliminary mammographic screenings are further investigated during diagnostic mammographic tests which use a high-resolution detector that is focused over the suspicious lesion. Typically, an area less than 100mm x 80mm, the current maximum size of our high-resolution scintillation plate, is interrogated. We show that diagnostic mammography, over an area of 100mm x 80mm, could be performed using our system with a feature resolution down to 7 microns.
In digital X-ray imaging, a crucial factor determining image resolution of all indirect detection systems is the spread of light in the X-ray scintillator. Currently deployed clinical x-ray detectors, with a resolution between 75 and 300 microns, are affected by such spread of light. This work demonstrates the significantly improved the resolution of an indirect X-ray scintillation detector using a new structuring approach The new structured scintillator consists of three main components: a high optical quality ‘channel plate’, a reflective material within the capillaries of the channel plate, and a polymer-based scintillating material that is incorporated in the capillaries. Channel plates, which are utilized for a variety of optical applications, are produced from bundles of hollow drawn borosilicate glass fibers, with repeated bundling and drawing reducing the diameter of the core and capillary pores down to values as low as 5 microns. These bundles are then cut to make high quality plates (‘channel plates’) with a thickness around 1 mm. Channel plates contain geometrically ordered capillary channels (about 5 million channels per square cm). The channel walls were coated with a 70 nm thick coating of Al2O3:W using atomic layer deposition (ALD) to optically confine the photoemission within the channel. The optical channel plates were infiltrated with a new bismuth-based scintillating polymer developed at Lawrence Livermore National Laboratory, with a photon yield of > 30,600 photons/keV for X-ray energies of 20-30 keV, a range of interest for mammography. The new scintillator plate was used to experimentally demonstrate an X-ray resolution of 10 microns (or 50 linepairs/ mm), an approximately 7 times improvement over existing scintillating detectors. A structured scintillator plate, coupled with a digital detection system may be used to improve the spatial resolution in applications such as mammography, radiography, and computed tomography.
Microchannel plates have been made by combining glass capillary substrates with thin films. The films impart the resistance and secondary electron emission (SEE) properties of the MCP. This approach permits separate choices for the type of glass, the MCP resistance and the SEE material. For example, the glass may be chosen to provide mechanical strength, a high open area ratio, or a low potassium-40 concentration to minimize dark rates. The resistive film composition may be tuned to provide the desired resistance, depending on the power budget and anticipated count rate. Finally, the SEE material may be chosen by balancing requirements for gain, long term stability of gain with extracted charge, and tolerance to air exposure.
Microchannel plates have been fabricated by Incom Inc., in collaboration with Argonne National Laboratory and UC Berkeley. Glass substrates with microchannel diameters of 10 and 20 microns have been used, typically with a length to diameter ratio of 60:1. Thin films for resistance and SEE are applied using Atomic Layer Deposition (ALD). The ALD technique provides a film with uniform thickness throughout the high aspect ratio microchannels. MCPs have been made in sizes up to 8”x8”. This three-component method for manufacturing MCPs also makes non-planar, curved MCPs possible.
Life testing results will be presented for 10 and 20 micron, 60:1 l/d ratio MCPs, with an aluminum oxide SEE film and two types of glass substrates. Results will include measurements of resistance, dark count rates, gain, and pulse height distributions as a function of extracted charge.
Atomic layer deposition (ALD) has enabled the development of a new technology for fabricating microchannel plates (MCPs) with improved performance that offer transformative benefits to a wide variety of applications. Incom uses a “hollow-core” process for fabricating glass capillary array (GCA) plates consisting of millions of micrometer-sized glass microchannels fused together in a regular pattern. The resistive and secondary electron emissive (SEE) functions necessary for electron amplification are applied to the GCA microchannels by ALD, which – in contrast to conventional MCP manufacturing– enables independent tuning of both resistance and SEE to maximize and customize MCP performance.
Incom is currently developing MCPs that operate at cryogenic temperatures and across wide temperature ranges. The resistive layers in both, conventional and ALD-MCPs, exhibit semiconductor-like behavior and therefore a negative thermal coefficient of resistance (TCR): when the MCP is cooled, the resistance increases, and when heated, the resistance drops. Consequently, the resistance of each MCP must be tailored for the intended operating temperature. This sensitivity to temperature changes presents a challenge for many terrestrial and space based applications.
The resistivity of the ALD-nanocomposite material can be tuned over a wide range. The material’s (thermo-) electrical properties depend on film thickness, composition, nanostructure, and the chemical nature of the dielectric and metal components. We show how the structure-property relationships developed in this work can be used to design MCPs that operate reliably at cryogenic temperatures. We also present data on how the resistive material’s TCR characteristics can be improved to enable MCPs operating across wider temperature ranges than currently possible.
Bundles of hollow glass capillaries can be tapered to produce quasi-focusing x-ray optics. These optics are known
as Kumakhov lenses. These optics are interesting for lab-based sources because they can be used to collimate
and concentrate x-rays originating from a point, such as a laser focus or an electron-beam focus in a microtube.
We report pilot production and advanced development performance results achieved for Large Area Picosecond
Photodetectors (LAPPD). The LAPPD is a microchannel plate (MCP) based photodetector, capable of imaging with
single-photon sensitivity at high spatial and temporal resolutions in a hermetic package with an active area of 400 square
centimeters. In December 2015, Incom Inc. completed installation of equipment and facilities for demonstration of
early stage pilot production of LAPPD. Initial fabrication trials commenced in January 2016. The “baseline” LAPPD
employs an all-glass hermetic package with top and bottom plates and sidewalls made of borosilicate float glass. Signals
are generated by a bi-alkali Na2KSb photocathode and amplified with a stacked chevron pair of “next generation” MCPs
produced by applying resistive and emissive atomic layer deposition coatings to borosilicate glass capillary array (GCA)
substrates. Signals are collected on RF strip-line anodes applied to the bottom plates which exit the detector via pinfree
hermetic seals under the side walls. Prior tests show that LAPPDs have electron gains greater than 107, submillimeter
space resolution for large pulses and several mm for single photons, time resolutions of 50 picoseconds for
single photons, predicted resolution of less than 5 picoseconds for large pulses, high stability versus charge extraction,
and good uniformity. LAPPD performance results for product produced during the first half of 2016 will be reviewed.
Recent advances in the development of LAPPD will also be reviewed, as the baseline design is adapted to meet the
requirements for a wide range of emerging application. These include a novel ceramic package design, ALD coated
MCPs optimized to have a low temperature coefficient of resistance (TCR) and further advances to adapt the LAPPD
for cryogenic applications using Liquid Argon (LAr). These developments will meet the needs for DOE-supported RD
for the Deep Underground Neutrino Experiment (DUNE), nuclear physics applications such as EIC, medical, homeland
security and astronomical applications for direct and indirect photon detection.
Mark Popecki, Daniel Bennis, Bernhard Adams, Aileen O'Mahony, Christopher Craven, Michael Foley, Michael Minot, Joseph Renaud, Justin Bond, Michael Stochaj, Klaus Attenkofer, Eli Stavitski
A new spectrometer design that will result in a highly efficient, easy to handle, low-cost, high-resolution spectroscopy system with excellent background suppression is being developed for the NSLS-II Inner-Shell Spectroscopy beamline. This system utilizes non-diffractive optics comprised of fused and directed glass capillary tubes that will be used to collect and pre-collimate fluorescence photons. There are several advantages enabled by this design; a large energy range is accessible without modifying the s-stem, a large collection angle is achieved per detection unit: 4-5% of the full solid angle, easy integration in complex and harsh environments is enabled due to the use of a pre-collimation system as a secondary source for the spectrometer, and background from a complex sample environment can be easily and efficiently suppressed.
The polycapillary X-ray focusing optics segment of this application has been under development. This includes improvement in manufacturing methods of polycapillary structure for x-ray optics, forming the polycapillary structure to produce X-ray optics to achieve the required solid angle collection and transmission efficiency, and measurement of X-ray focusing properties of the optics using an X-ray source. Two promising advances are large open area ratios of 80% or more, and the possibility of adding coatings in the capillaries using Atomic Layer Deposition techniques to improve reflection efficiency.
We demonstrate a cost-effective and robust route to fabricate large-area microchannel plate (MCP) detectors, which
will open new potential in larger area MCP-based detector technologies. For the first time, using our newly
developed process flow we have fabricated large area (8"x8") MCPs. We used atomic layer deposition (ALD), a
powerful thin film deposition technique, to tailor the electrical resistance and secondary electron emission (SEE)
properties of large area, low cost, borosilicate glass capillary arrays. The self limiting growth mechanism in ALD
allows atomic level control over the thickness and composition of resistive and SEES layers that can be deposited
conformally on high aspect ratio capillary glass arrays. We have developed several robust and reliable ALD
processes for the resistive coatings and SEE layers to give us precise control over the resistance (106-1010Ω) and
SEE coefficient (up to 5). This novel approach allows the functionalization of microporous, insulating substrates to
produce MCPs with high gain and low noise. These capabilities allow a separation of the substrate material
properties from the amplification properties. Here we describe a complete process flow to produce large area MCPs.
A crystal-optic x-ray fluorescence analyzer has been designed and tested, which combines the features of electron-Volt
energy resolution, large solid angle coverage, and tunability over several thousand electron-Volts. Dependent on
experimental requirements the crystal shape can be chosen within the elasticity limits of the crystal. This allows the use
of the device not only for high resolution X-ray spectroscopy, but also for imaging purposes. We present the basic
design, a self-alignment algorithm, and a basic discussion about the principal feasibilities and limitations of this concept.
Additionally, first experimental results on ultra dilute systems and other applications will be presented.
A way is proposed to obtain pulses of visible/infrared light in femtosecond synchronism with x-rays from an x-ray free-electron laser (XFEL), using the recently proposed emittance-slicing technique. In an XFEL undulator, only the short section of an electron bunch whose emittance is left unchanged by the slicing will emit intense coherent x-rays in the XFEL undulator. At the same time, the bunch emits highly collimated transition undulator radiation (TUR) into a cone whose opening angle is the reciprocal relativisticity parameter gamma. Due to the variation of the transverse momentum induced by the emittance slicing, the effective number of charges contributing to the TUR varies along the bunch, and is higher in the sliced-out part that emits the coherent x-rays. As with coherent synchrotron radiation (CSR), the TUR is thus coherently enhanced (CTUR) at near-infrared wavelengths. Coming from the same part of the bunch the CTUR and the coherent x-rays are perfectly synchronized to each other. Because both types of radiation are generated in the long straight XFEL undulator, there are no dispersion effects that might induce a timing jitter. With typical XFEL parameters, the energy content of the single optical cycle of near-IR CTUR light is about 100 Nano-Joule, which is quite sufficient for most pump-probe experiments.
The dynamical theory of x-ray diffraction is extended in the form of an explicitly time-dependent synthesis of the Takagi-Taupin and eikonal theories of x-ray diffraction. Being based upon microscopic electromagnetism, the theory can describe time dependence on subpicosecond timescales. Several x-ray optical elements are proposed
for the subpicosecond manipulation of x-rays.
The diffraction of x-rays in crystalline materials is governed by the amplitudes of the Fourier transform of the electron density, commonly called the structure factors. A change in these amplitudes can be induced by a high-power laser and can lead to a number of interesting effects, like a sweep of the beam propagation direction that could be used for a device for time-resolved x-ray detection that bears some similarity to a streak camera and can potentially reach few-femtosecond resolution. Another effect that becomes relevant on subpicosecond timescales is the generation of frequency-shifted x-rays, which could be used in Mossbauer spectroscopy, or for the concentration of x-ray photons into a narrow energy band. Even small changes in the structure factors can produce a large effect through coherent interaction with the x-rays in a large crystalline volume. A theoretical treatment, based on the Takagi-Taupin theory of dynamical diffraction, is presented.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.