The newest Gas Cherenkov Detector (GCD-3) diagnostic has completed its Phase I commissioning/milestone at the
National Ignition Facility (NIF). GCD-3 was fielded for several years at the Omega Laser Facility in its initial
configuration, before being moved to the NIF. Installation at the NIF involved optimization of GCD-3 for the higher
background environment and designing a new insertion carrier assembly. GCD-3 serves as the initial phase towards the
implementation of the “Super GCD” (SGCD) at the NIF. During this phase of development GCD-3 took measurements
from a re-entrant well, 3.9 meters from target chamber center (TCC). Plans to insert GCD-3 within 20 cm of TCC with a
Target and Diagnostic Manipulator (TANDM) will be discussed. Data was collected using a Photomultiplier Tube
(PMT) in combination with a Mach-Zehnder based recording system. These measurements were used to aid in shielding
analysis, validate MCNP models, and fuel design efforts for the SGCD. Findings from the initial data will be covered
extensively, including an in-depth look into sources of background and possible mitigation strategies. Ongoing
development of phase two, the addition of an ultra-high bandwidth Pulse Dilatation Photomultiplier Tube (PD-PMT),
will also be presented.
The fusion diagnostic community require optical recording instruments with precise time resolution covering a dynamic range of many orders of magnitude. In 2012 the Laboratory for Laser Energetics, Photek and Sydor Instruments embarked on the re-design of an improved streak tube for fusion diagnostics. As a baseline, we started with the Photek STY streak tube because the tube body can accommodate a 35 mm long photocathode. Electron optical modelling was carried out by both Paul Jaanimagi in the US and by Photek in a parallel exercise. Many changes and modifications were made: the time resolution was improved to 5 ps, the usable cathode length was increased from 20mm to 32 mm under high extraction field operation and the off-axis spatial resolution was substantially improved compared to other tubes of this format. Several tubes have been built and tested in a Sydor ROSS-5800 streak cameras, and show greatly improved resolution (MTF).
Time-correlated single photon counting (TCSPC) is a widely used, sensitive, precise, robust and mature technique to measure photon arrival times in applications such as fluorescence spectroscopy and microscopy, light detection and ranging (lidar) and optical tomography. Wide-field TCSPC detection techniques, where the position and the arrival time of the photons are recorded simultaneously, have seen several advances in the last few years, from the microsecond to the picosecond time scale. Here, we summarise some of our recent work in this field with emphasis on microsecond resolution phosphorescence lifetime imaging (PLIM) and nanosecond fluorescence lifetime imaging (FLIM) microscopy.
This paper reviews recent European developments in imaging photomultiplier technology.
Photocathode technology is well established and has been optimised for a variety of applications; for example, the multi
alkali cathode has deep UV response optimised for Cerenkov detectors in particle physics and also for use in UV laser
inspection systems. Telluride based cathodes have been substantially improved for both astronomical and solar blind
Recent developments have significantly advanced the time resolution limits of MCP based photomultipliers; this is of
particular importance for applications in nuclear physics. The same technology is driving multi-pixel photomultiplier
developments for biological applications.
Gate units designed using a push-pull MOSFET output for single nanosecond ultra-fast electronic shuttering (or
"gating") of image intensifiers or photomultipliers normally have to be tuned to fit the capacitance load of the detector
being gated. Photek has developed a self-tuning gate unit that automatically achieves the fastest possible gating speed for
any capacitance load up to 250 pF. We demonstrate an exposure time of 2 ns for a 9 mm × 9 mm segment on a 40 mm
diameter detector divided into 8 segments for high speed framing. The same gate unit is capable of an exposure time of
10 ns for a full 75 mm diameter working area detector. We also demonstrate transition times in single nanoseconds from
"OFF" to fully "ON" on large area ultrafast photomultipliers tubes. Sub-nanosecond gate units based on avalanche
technology are often limited to short gate exposures or are unable to achieve d.c. operation. This new development has a
fully flexible output that follows the TTL trigger input right up to d.c. exposure and is capable of repetition rates up to
We have developed single photon counting image intensifier tubes combining position and time information read-out with at least 500x500 pixels and sub-nanosecond time resolution. This image intensifier type uses a resistive screen instead of a phosphor screen and the image charge pickup anode is placed outside the sealed tube. We present a novel delay-line anode design which allows for instance detecting simultaneously arriving pairs of photons. Due to the very low background this technique is suited for applications with very low light intensity and especially if a precise time tagging for each photon is required. We show results obtained with several anode types on a 25 mm image intensifier tube and a 40 mm open-face MCP detector and discuss the performance in neutron radiography, e.g. for homeland security, and the prospects for applications like Fluorescence Life-time Imaging Microscopy (FLIM), astronomy and X-ray polarimetry.
We have developed image intensifier tubes with delay-anode read-out for time- and position-sensitive photon
counting. The timing precision is better than 1 ns with 1000x1000 pixels position resolution and up to one megacounts/s
processing rate. Large format detectors of 40 and 75 mm active diameter with internal helical-wire delay-line anodes
have been produced and specified. A different type of 40 and 25 mm tubes with semi-conducting screen for image
charge read-out allow for an economic and robust tube design and for placing the read-out anodes outside the sealed
housing. Two types of external delay-line anodes, i.e. pick-up electrodes for the image charge, have been tested. We
present tests of the detector and anode performance. Due to the low background this technique is well suited for
applications with very low light intensity and especially if a precise time tagging for each photon is required. As an
example we present the application of scintillator read-out in time-of-flight (TOF) neutron radiography. Further
applications so far are Fluorescence Life-time Microscopy (FLIM) and Astronomy.
The Image Dissector was one of the first all electronic TV tubes and was described by Farnsworth in 1934. (Ref 1).
Fifty years later, in 1983, more modern image dissectors were used to measure the electron bunch lengths in
synchrotrons. The advent of modern computers and high-speed electronics enables these rather elderly tubes to be used
in exciting new applications.
This paper described how we have adapted the image dissector to enable the development of low cost instruments with
exceptional bandwidth, sensitivity and sampling rate for optical signals.
We have designed and built a sealed tube microchannel plate (MCP) intensifier for optical/NUV photon counting applications suitable for 18, 25 and 40 mm diameter formats. The intensifier uses an electronic image readout to provide direct conversion of event position into electronic signals, without the drawbacks associated with phosphor screens and subsequent optical detection. The Image Charge technique is used to remove the readout from the intensifier vacuum enclosure, obviating the requirement for additional electrical vacuum feedthroughs and for the readout pattern to be UHV compatible. The charge signal from an MCP intensifier is capacitively coupled via a thin dielectric vacuum window to the electronic image readout, which is external to the sealed intensifier tube. The readout pattern is a separate item held in proximity to the dielectric window and can be easily detached, making the system easily reconfigurable. Since the readout pattern detects induced charge and is external to the tube, it can be constructed as a multilayer, eliminating the requirement for narrow insulator gaps and allowing it to be constructed using standard PCB manufacturing tolerances. We describe two readout patterns, the tetra wedge anode (TWA), an optimized 4 electrode device similar to the wedge and strip anode (WSA) but with a factor 2 improvement in resolution, and an 8 channel high speed 50 ohm device, both manufactured as multilayer PCBs. We present results of the detector imaging performance, image resolution, linearity and stability, and discuss the development of an integrated readout and electronics device based on these designs.
The output pulse width in the time response of photo-multiplier tubes (PMT) is much faster in micro-channel plate (MCP) models compared to more standard dynode chain PMTs due to a vastly reduced variation in the path length of the electrons through the amplifying system. Typically the pulse widths can be in the region of 200ps compared to the nanosecond domain occupied by the best conventional PMTs. Photek manufacture PMTs with one, two or three MCPs depending on the gain required, and also use the same structure without any MCPs to work as simple photodiodes. We demonstrate the variation of output pulse characteristics due to the number and design of MCPs in a range of PMT models and illustrate the importance of having a properly designed 50ohm transmission line to deliver the pulse from the detector.
Previously we have described several types of charge division electronic image readouts for microchannel plate based imaging detectors developed at MSSL, primarily for space astronomy applications. These have included the wedge and strip anode<SUP>1</SUP> (WSA), the Vernier anode<SUP>2</SUP> - a high resolution readout, capable of exploiting the limiting spatial resolution offered by the microchannel plate, and FIRE<SUP>3</SUP> - an imaging device operating at event rates in excess of 10 MHz. MSSL and Photek have now joined in collaboration to develop an intensifier based imaging system designed to employ this range of readout systems for general laboratory use. The image intensifier uses the image charge technique<SUP>4,5</SUP> whereby the event charge is used to induce electrical signals on the capacitively coupled readout pattern, obviating the requirement for the readout to be inside the vacuum enclosure. The image readout is manufactured as a separate component, and can be interchanged to suit the specific application requirements. The intensifier tube design can be generic enabling it to be used with a variety if image readouts designs. We describe the image intensifier and electronic design, including the common charge amplifier, event timing and computer interface. We discuss the anticipated performance of the various readout systems - Wedge and Strip, Vernier and FIRE in terms of spatial resolution, maximum count rate, and timing resolution.