Microchannel Plate Image Intensifier Research Articles

Ultrafast optical gated image intensifier with a temporal resolution of 230 picosecond using uniform underlayer

An Au uniform photocathode underlayer is employed in this paper to obtain picosecond (ps) optical gating width for image intensifier tube. The transmittances and gating pulse transmission efficiencies of the underlayer with different thicknesses are tested and compared to determine the optimal thickness. An 18 mm diameter proximity focused microchannel plate image intensifier tube with S25 photocathode is fabricated using this uniform underlayer. The profile measurement shows the tube has an optical gating time as low as 230 ps full width at half maximum (FWHM) when gated with a 176 ps width gating pulse. The measured iris delay is between 83 ps and 108 ps, which approaches the theoretical limit of its kind.

Two-axis XUV/SR Imaging System with Temporal-spatial Resolution for Wire Array Z-pinch on Qin-1

Qin-1 is a Z-pinch pulse power generator. Due to the diagnostic requirements of its wire array Z-pinch, a two-axis temporal-spatial resolution XUV/SR imaging system has been developed. The system is composed of filters, two gated pinhole cameras, and a synchronized electric control system. Each camera consists of a pinhole array, a four-frame microchannel plate image intensifier and a CMOS camera. The whole system can synchronously diagnose plasma from two directions with a time resolution of 3 ns. The spatial resolution of the system is approximately 51 μm when the diameter of the pinhole is 20 μm and incident radiation is greater than 455 eV. By using the system, the implosion of symmetric loads and asymmetric loads was investigated. The generation, ablation and compression of the coronal plasma and instabilities in the implosion axis at stagnation can be directly observed from two views. The results indicated that the position of the implosion axis is related to the mass distribution of the wire array and provided more details about bright spots on individual wire arrays. In addition, the diagnostic results of a single wire with energy resolution were acquired.

A MOSFET-based high voltage nanosecond pulse module for the gating of proximity-focused microchannel plate image-intensifier

Gate modules based on avalanche technology for photocathode gating to proximity-focused microchannel-plate image intensifier (MCPII) are often limited to short gate exposures. A nanosecond pulse module based on MOSFET devices has been demonstrated at our lab, which is capable of generating pulses of adjustable full width at half maximum (FWHM) from 3 ns to D.C. operation with 1 ns switching time and a burst repetition rate up to 4 MHz. A method of supplying gate-current pulses to the MOSFET device is adopted to increase the switching speed based on the totem pole driver. Nanosecond optical gating time of an 18-mm proximity-focused MCPII with a metallic underlay photocathode was obtained. A MCPII with standard multi-alkali photocathode was analyzed for comparison. Moreover, a photocathode-MCP model based on the Finite Integral Technique (FIT) is developed to investigate the dependence of the gating time on the sheet resistance of the photocathode.

Performance Evaluation of the Thick Pinhole Gamma Rays Diagnostic System

The diagnostic methods for the profile of the radiation source were estab-lished at first based on the pinhole imaging principle. In this paper, the relationships among various parameters of the gamma-rays crammer such as the modulation transfer function (MTF), the noise power spectrum (NPS), the signal-noise ratio (SNR) and the detective quantum efficiency (DQE) are developed and studied experimentally on the cobalt radiation source. The image diagnostic system is consisting with rays-fluorescence convertor (YAG crystal), optical imaging system, MCP image intensifier, CCD camera and other devices. The spatial resolution of the modulation transfer function (MTF) at 10% intensity was measured as 1 lp/mm by knife-edge method. The quantum of the measurement system is about 150 under weak radiation condition due to the single particle detection efficiency of the system. The dynamic range was inferred preliminarily as about 437. The required radiation intensity was calculated using the experiment result for the (SNR) = 1, 5, 10, respectively. The theoretical investigation results show that the radiation image with (SNR) = 1 can be only obtained when the pinhole diameter is 0.7 mm, object distance and image distance are both 200 cm, and the radiation intensity is about 1.0 × 1012 Sr-1·cm-2.

Evaluation of Major Factors Affecting Spatial Resolution of Gamma-Rays Camera

Gamma-rays camera is mainly used in image diagnostics of intense pulse radiation sources. The spatial resolution of the camera was measured on a 60Co gamma-rays source with edge method. The spatial resolution MTF (modulation transfer function) at the 10% intensity was about 2 lp/mm and the maximal single-noise ratio (SNR) of the camera was found to be about 5:1. In addition, the spatial resolution of the camera was measured with pulse X-rays with 0.3 MeV in average energy and exclusion of effects of secondary electrons from consideration. Accordingly, the spatial resolution MTF at the 10% intensity was about 5lp/mm, verifying effects of secondary electrons induced by 1.25MeV gamma-rays in the scintillator upon the spatial resolution. Based on our analysis, dispersion sizes of secondary electrons in the scintillator are about 0.4 mm∼0.6 mm. Comparatively, as indicated by detailed analysis of spatial resolutions of the MCP image intensifier and CCD devices, both have little effect on the camera's spatial resolution and could be well neglected.

Four-dimensional positron age-momentum correlation

We have performed first four-dimensional age-momentum correlation (4D-AMOC) measurements at a pulsed high intensity positron micro beam and determined the absolute value of the three-dimensional momentum of the electrons annihilating with the positrons in coincidence with the positron age in the sample material. We operated two position sensitive detectors in coincidence to measure the annihilation radiation: a pixelated HPGe-detector and a microchannel plate image intensifier with a CeBr3 scintillator pixel array. The transversal momentum resolution of the 4D-AMOC setup was measured to be about 17 × 10−3 (FWHM) and was circa 3.5 times larger than the longitudinal momentum resolution. The total time resolution was 540 ps (FWHM). We measured two samples: a gold foil and a carbon tape at a positron implantation energy of 2 keV. For each sample discrete electron momentum states and their respective positron lifetimes were extracted.

Position and time resolution measurements with a microchannel plate image intensifier: A comparison of monolithic and pixelated CeBr3 scintillators

To perform Four Dimensional Age Momentum Correlation measurements in the near future, where one obtains the positron lifetime in coincidence with the three dimensional momentum of the electron annihilating with the positron, we have investigated the time and position resolution of two CeBr3 scintillators (monolithic and an array of pixels) using a Photek IPD340/Q/BI/RS microchannel plate image intensifier. The microchannel plate image intensifier has an active diameter of 40mm and a stack of two microchannel plates in chevron configuration. The monolithic CeBr3 scintillator was cylindrically shaped with a diameter of 40mm and a height of 5mm. The pixelated scintillator array covered the whole active area of the microchannel plate image intensifier and the shape of each pixel was 2.5·2.5·8mm3 with a pixel pitch of 3.3mm. For the monolithic setup the measured mean single time resolution was 330ps (FWHM) at a gamma energy of 511keV. No significant dependence on the position was detected. The position resolution at the center of the monolithic scintillator was about 2.5mm (FWHM) at a gamma energy of 662keV. The single time resolution of the pixelated crystal setup reached 320ps (FWHM) in the region of the center of the active area of the microchannel plate image intensifier. The position resolution was limited by the cross-section of the pixels. The gamma energy for the pixel setup measurements was 511keV.

Development of a new time and position resolving detector for the pulsed low energy positron system PLEPS

The pulsed low energy positron system PLEPS at the Munich research reactor FRM-II is a user facility for depth resolved positron lifetime measurements. Besides positron lifetime measurements 2D-AMOC (Two Dimensional Age Momentum Correlation) experiments are also possible. 2D-AMOC provides in coincidence the lifetime of the positron and the longitudinal momentum distribution of the annihilated electron. It would be of great scientific concern to measure simultaneously the entire 3D-momentum distribution of the electron annihilating with the positron and the corresponding lifetime of the positron (4D-AMOC). To perform 4D-AMOC measurements a time and position resolving detector is required in coincidence with a pixelated Germanium detector. Therefore a time and spatially resolving detector is currently developed at our institute with envisaged time resolution of 100 ps (FWHM) and a spatial resolution of about 2.6 mm (FWHM) over an area of 12 cm2. First test measurements have been carried out with a 25 mm diameter MCP (Micro Channel Plate) image intensifier and with special delay-line anode readout for the spatial information. Up to now 178 ps (FWHM) time resolution and on average 3.4 mm (FWHM) position resolution have been achieved with BaF2 as scintillator material and a 60Co source.

Formation mechanism of “memory” phenomenon of microchannel plate image intensifier

A discrete resistance capacitance dynodes chain of channel multiplication model worked in a continuous variable dynode number described here is an attempt to explain the formation mechanism of “memory” phenomenon of microchannel plate image intensifier, wherein it was concluded conclusion that “memory” phenomenon of image intensifiers were the results of a silicon-rich layer, which existed between emission layer and conduction layer of channel inner wall of microchannel plate, having much higher resistance as compared with the conduction layer, and there are two distinct appearance ways of “negative memory” and “positive memory” only due to a difference in illumination and duration of the image intensifier suffered, and a strictly controlled MCP manufacture process would make considerable reduction of “memory” phenomenon occurrence ratio.

Evaluation of Major Factors Affecting Spatial Resolution of Gamma-Rays Camera

The spatial resolution of the gamma-rays camera was measured on a60Co gamma-rays source with edge method. The gamma-rays camera is consisting with rays-fluorescence convertor, optical imaging system, MCP image intensifier, CCD camera, electronic control system and other devices, and is mainly used in the image diagnostics of the intense pulse radiation sources [1]. Due to the relatively big quantum detective efficiency (DQE) and quantum gain of the gamma-rays, etc., the experimental data were processed by averaging multiple images and fitting curves. According to the experimental results, the spatial resolution MTF (modulation transfer function) at the 10% intensity was about 2lp/mm. Meanwhile, because of the relatively big dispersion effects of the fluorescence transmissions in the scintillator and the optical imaging system, the maximal single-noise ratio (SNR) of the camera was found to be about 5:1. In addition, the spatial resolution of the camera was measured with pulse X-rays with 0.3MeV in average energy and exclusion of the effects of secondary electrons from consideration. Accordingly, the spatial resolution MTF at the 10% intensity was about 5lp/mm. This could be an additional evidence to verify the effects of secondary electrons induced by the 1.25MeV gamma-rays in the scintillator upon the spatial resolution. Based on our analysis, the dispersion sizes of the secondary electrons in the scintillator are about 0.4mm-0.6mm. Comparatively, as indicated by the detailed analysis of the spatial resolutions of the MCP image intensifier and CCD devices, both of them have little effect on the spatial resolution of the gamma-rays camera that could be well neglected.

Dynamic States of Heavy Hydrocarbon-Oxygen Premixed Flames on an Annular Burner

The spatial and temporal characteristics of dynamic states of premixed flames on an annular burner are found to be significantly different from the characteristics of the dynamic states observed on a circular burner. At increasingly larger values of a control parameter of heavy hydrocarbon-oxygen mixtures, the steady, uniform, annular front is replaced by a sequence of time-dependent states in which bright spots, highly localized regions of optical emission, move rapidly around the annulus. These particle-like objects appear spontaneously, individually, or in counterpropagating pairs, move in either direction, collide, and annihilate. A high speed camera equipped with a microchannel plate image intensifier is used to record this $>35$ Hz motion. Video sequences of these states are embedded in this presentation in order to demonstrate how the nonperiodic nature of this dynamics evolves at increasing values of the driving parameter. Our results are compared with the findings of numerical studies by Bayliss and Matkowsky on solid fuel combustion in an annular geometry.

Development of an advanced X-ray detector for inspecting inner microscopic structural details in industrial applications

A new charge coupled device (CCD)-based X-ray detector, which uses a high-gain microchannel plate image intensifier for upfront optical gain, is proposed. The intensifier is directly coupled with the photosensitive surface of a CCD by a fiber optic taper and acts as both a converter and intensifier. Experimental results for the detector in X-ray imaging show that the detector currently has an intrinsic resolution of approximately 83 μm (12 lp/mm).

Synchrotron radiation microdiffraction of ballistic molten wax microdrops

Using stroboscopic techniques, diffraction patterns of ballistic paraffin wax microdrops have been observed. The microdrops, generated by a high-temperature ink-jet system, travel through the 1 mum synchrotron radiation beam with a speed of about 1.4 m/s. Diffraction patterns were recorded in flight by a charge couple device with a microchannel plate image intensifier stage, which was activated with the microdrop generation frequency of 1000 Hz during 2 mus. The data show liquid microdrops with a constant temperature up to 8 mm from the ink-jet system capillary exit. The general technique could be adapted for studying fast structural processes, such as protein conformational changes in aqueous microdrops.

Dynamic modulation transfer function measurement of image intensifiers using a narrow slit

Modulation transfer function (MTF) is an important figure of image resolution of microchannel plate image intensifiers (MCPIIs). Dynamic MTFs of two Gen-II MCPIIs were measured under pulsed voltage operation (gated mode) using a narrow slit. The resolution determined by the MTF was calculated under various bias voltages and gate widths. Our numerical results show that with the increase of the reverse bias of MCPIIs, the resolution is improved rapidly below 40 V and then gradually decreased. With the MCP bias increased, both MCPIIs start to suffer rapid reductions in resolution at 800 and 750 V, respectively. The change of phosphor voltage has little influence on the resolution. The resolution declines rapidly with the decrease of the gate width below 20 ns but goes steady above 30 ns. We explored causes of these variations.

High speed photon-counting imager using a position sensitive diode

A new use for a 2-dimensional position sensitive diode (PSD) is described. A duolateral PSD was used with a microchannel plate image intensifier as a proof-of-concept photon counting (event driven) imager for astronomical imaging and photometry. This produced an imager capable of counting 25–30 kcps over the astronomical bands B, V & R, with an overall efficiency of ∼19%.

Transmission grating spectrograph with on-line recording of XUV soft X-ray spectra from laser produced plasmas

The setting up and on-line operation of a transmission grating spectrograph in the XUV soft X-ray region is described. The detector was a microchannel plate–image intensifier combination, and the output of the image intensifier was coupled to a CCD camera–frame grabber system through an imaging lens. The spectrograph could be operated in the 5–20 Å range with 0.6 Å spectral resolution and in the 5–50 Å range with ∼1 Å resolution, respectively. The high sensitivity of the detector enables single shot operation, which is useful for several laser plasma interaction studies.

Time-dependent spectroscopy of plasma plume under laser welding conditions

Momentary emission spectra of iron and argon lines were measured in a plasma plume induced during welding with a continuous wave CO2 laser. Time-dependent spectra were registered using a fast gate, lens coupled microchannel plate image intensifier placed between a spectrograph and a 1254 silicon intensified target detector connected to an optical multichannel analyser. The results, together with the analysis of the colour images from a fast camera, show that in the case when argon is the shielding gas, two plasmas exist: the argon plasma and the iron plasma. It has been found that during strong bursts the plasma plume over the keyhole consists mainly of metal vapour, not being diluted by the shielding gas. No apparent mixing of the metal vapour and the shielding gas has been observed. The space-averaged electron densities determined from the Stark broadening of the 7503.87, 7514.65 Å Ar I lines amounts to (0.75–1.05) × 1023 m−3 depending on the distance from the surface. Assuming that argon is not mixed with the metal vapour and is in local thermodynamic equilibrium these electron densities correspond to the temperatures of 12–13 kK. At the peaks of strong vapour bursts the space-averaged electron densities determined from the Stark broadening of the 5383.37 Å Fe I line are (0.6–1) × 1023 m−3. Numerical simulations showed that the maximum densities in the plasma centre are considerably higher and amount to ∼1.8 × 1023 m−3 and ∼2.45 × 1023 m−3 in the case of the argon and metal plasma, respectively. Consequently the absorption of the laser beam in the plasma plume amounts to ∼5% of the beam power in the case of argon and 10% in the case of metal plasma.

Spectroscopic measurements of plasma plume induced during the laser deposition of the hydroxyapatite

Plasma plume induced by ArF exeimer laser ablation of a Ca10(PO4)6(OH)2 hydroxyapatite target during deposition process has been studied in different ambient conditions, i.e. in air or water vapour. ArF laser operated at the wavelength of 193 nm with the pulse energy of 300 mJ and 20 ns pulse duration. Spectroscopic measurements of the emission spectra of plasma plume have been made with the use of a fast gate, lens coupled micro-channel plate (MCP) image intensifier placed between a spectrograph and a 1254 silicon intensified target (SIT) detector connected to an optical multichannel analyser. The electron densities of 1022 ÷ 1023m−3 have been determined from the Stark broadening of Ca I lines as a function of the distance from the target. The expansion of the plasma plume has been studied using the time of flight method. The time-dependent radiation of the 422.673 nm Ca I and 393.366 nm Ca II lines has been, registered with the use of a monochromator and photomultiplier at various distances from the target. Velocities between 104 ÷ 103 m/s have been found. The velocity in air is several times higher than in the case with water vapour. The plasma plume dynamics is also different in both cases. In the presence of water vapour the spliting of the plasma plume appears.

PhiFLIM: a new method to avoid aliasing in frequency-domain fluorescence lifetime imaging microscopy.

In conventional wide-field frequency-domain fluorescence lifetime imaging microscopy (FLIM), excitation light is intensity-modulated at megahertz frequencies. Emitted fluorescence is recorded by a CCD camera through an image intensifier, which is modulated at the same frequency. From images recorded at various phase differences between excitation and intensifier gain modulation, the phase and modulation depth of the emitted light is obtained. The fluorescence lifetime is determined from the delay and the decrease in modulation depth of the emission relative to the excitation. A minimum of three images is required, but in this case measurements become susceptible to aliasing caused by the presence of higher harmonics. Taking more images to avoid this is not always possible owing to phototoxicity or movement. A method is introduced, phiFLIM, requiring only three recordings that is not susceptible to aliasing. The phase difference between the excitation and the intensifier is scanned over the entire 360 degrees range following a predefined phase profile, during which the image produced by the intensifier is integrated onto the CCD camera, yielding a single image. Three different images are produced following this procedure, each with a different phase profile. Measurements were performed with a conventional wide-field frequency-domain FLIM system based on an acousto-optic modulator for modulation of the excitation and a microchannel-plate image intensifier coupled to a CCD camera for the detection. By analysis of the harmonic content of measured signals it was found that the third harmonic was effectively the highest present. Using the conventional method with three recordings, phase errors due to aliasing of up to +/- 29 degrees and modulation depth errors of up to 30% were found. Errors in lifetimes of YFP-transfected HeLa cells were as high as 100%. With phiFLIM, using the same specimen and settings, systematic errors due to aliasing did not occur.

Development of a gated scintillation fiber neutron detector for areal density measurements of inertial confinement fusion capsules

A detector for fuel areal density measurements in inertial confinement fusion capsules has been designed. Observation of neutrons scattered in an imploded deuterium capsule (0.27–0.6 MeV) is a promising method for areal density measurements in the National Ignition Facility DD surrogate capsules. In order to detect scattered neutrons, we need to (1) suppress interference due to the strong direct neutron burst and (2) suppress the background produced by neutrons scattering on nontarget material (mainly from the target chamber). In our detector system, we suppress direct neutrons by gating the detector. We suppress the nontarget background neutrons by placing the detector outside the target chamber and limiting the view of the detector with collimators. In addition, we are developing a lithium-glass scintillation-fiber detector (LG-SCIFI) to detect the scattered neutrons. The LG-SCIFI will work as a multichannel scintillator array. The scintillation signal will be amplified by a microchannel plate image intensifier, which is gated to accept signals only in a specific time-of-flight window for the scattered neutrons. The gated scintillation image will be recorded by a charge-coupled device. Since the detector is segmented, neutron detection events will be clearly identified as bright spots in the gated image.