Microchannel Plate Intensifier Research Articles

Novel imaging technique for thermal neutrons using a fast optical camera

A novel imaging technique for thermal neutrons using a fast optical camera is presented. Thermal neutrons are reacted with 6Lithium to produce a pair of 2.73 MeV tritium and 2.05 MeV alpha particles, which in turn interact in a thin layer of LYSO crystal scintillator to produce a localized flash of light. These photons are directed by a pair of lenses to a micro-channel plate intensifier, and its output is connected to the optical camera, TPX3CAM. The results from the camera are reconstructed through a custom algorithm. Various cutting parameters were found through data analysis to eliminate the background, and they were shown effective in matching the simulated rate of the neutron source. The system is fast with 40 ns decay time and allows free-space light collection, both vastly enhances flexibility of neutron detection.

Focus on photonics, spectroscopy, and spectrometry

Focus on photonics, spectroscopy, and spectrometry

Preliminary Study on Possibility Cl Detection in Soil by Means of The Unique Sub-target in a Transversely Excited Atmospheric Pressure (TEA) Carbon Dioxide (CO2) Laser Induced Breakdown Spectroscopy

A preliminary study on Cl detection in soil sample using LIBS has been carried out. The soil sample was mixed with silicon grease to allow attachment to the surface of a nickel plate acting as a sub-target. The laser used in this work is a TEA CO2 laser that operates at wavelength of 10.6μm with energy and pulse duration of 2.5 J and 200 ns, respectively. The laser beam was focused onto the sample using a zinc selenium lens (f = 200 mm) under air and helium surrounding gas at atmospheric pressure. The emission spectrum from the generated plasma was detected using an optical multichannel analyser (OMA)system consisting of a 0.32-m-focal length spectrograph with a grating of 1200 graves/mm and a 1024-channel photodiode detector array with a micro-channel plate intensifier. Soil sample used in this work is a standard soil sample mixed with NaCl solution at various concentrations. The results show that many emission lines due to salts such as Ca, Mg, Na and K can be detected clearly. Nevertheless, Cl emission line cannot be detected in soil sample, although the sample has been intentionally mixed with Cl, even when Cl content reaching 1000 ppm. It is therefore necessary to develop a new approach to allow LIBS techniques for detecting Cl in soil samples.

Plasma induced by a pulsed CO2 laser from powder samples mixed with silicone on metal subtarget and its possibility for detecting difficult salts of Cl, B, and S

Emission spectrum from plasma produced by a transversely excited atmosphere (TEA) carbon dioxide (CO2) laser from pure powder samples mixed with silicone grease attached to a nickel plate was studied. The pulsed CO2 laser operating at wavelength of 10.6 μm with energy and duration of the laser pulse is 2.5 J and 200 ns, respectively. The plasma was produced by focusing the laser beam onto the sample using a focusing lens (f = +200 mm) under air and helium surrounding gas at atmospheric pressure alternatively. The plasma emission spectrum was detected using an optical multichannel analyser (OMA) system equipped with a 0.32-m-focal length spectrograph. The spectrograph consists of a grating of 1200 graves/mm and a 1024-channel photodiode detector array with a micro-channel plate intensifier. The samples used this work are pure chemical powder samples. This technique was used to investigate emission spectral lines due to important salts but difficult to detect such as boron (B), chlorine (Cl) and sulphur (S) from powder samples. It was found that emission intensity detected from the produced plasma is remarkably higher in case using He as ambient gas compared with that using air. It was found that emission spectral lines due to B, Cl, and S can clearly be detected. Even though concentration of the salts (B, Cl, S) is very high since the samples used are pure chemical powder, however several emission spectral lines theoretically expected to appear with strong relative intensity displays relatively low intensity in the detected spectrum. This result confirms the difficulty for detecting the salts, especially chlorine (Cl) and sulphur (S). This technique basically promises a potential application for direct detection of B, Cl and S from powder samples, however new approaches must be developed to realise a high sensitive detection especially for Cl and S.

Detection of salts in soil using transversely excited atmospheric (TEA) carbon dioxide (CO2) laser-induced breakdown spectroscopy (LIBS) by the aid of a metal mesh

In this work, a nickel metal mesh was used to allow a direct detection of salt in soil sample by LIBS utilizing unique characteristics of a TEA CO2. The metal mesh is placed in the front of the soil sample to prevent the soil sample from blowing off upon focusing the high pulsed laser beam irradiation. LIBS apparatus used in this work is a TEA CO2 laser operated at wavelength of 10.6 μm with pulse energy and duration of 3J and 200 ns, respectively. The laser beam was focused using a ZnSe lens (f = 200 mm) onto soil sample after passing through the metal mesh. The emission spectrum from the induced plasma was detected using an optical multichannel analyzer (OMA) system consisting of a 0.32-m-focal length spectrograph with a grating of 1200 graves/mm and a 1024-channel photodiode detector array with a micro-channel plate intensifier. The soil sample used is a standard soil and ordinary soil containing several salts such as Ca, Mg at high concentration. The LIBS experiment was carried out at high pressure surrounding gas of 1 atmosphere. It was observed that by the aid of the metal mesh, strong breakdown gas plasma can be produced just after TEA CO2 laser irradiation on soil sample without significant sample blowing off. It was found that emission lines from salts, Ca (Ca II 393. 3 nm, Ca II 396.3 nm, Ca I 422.5 nm), and also other salts including Mg and Na can clearly be detected with strong emission intensity and narrow spectral width. This result implies that a TEA CO2 LIBS assisted by the metal mesh (metal mesh method) can be used for direct analysis several salts such as Ca, Mg, and Na in soil sample.

Demountable readout technologies for optical image intensifiers

We describe a generic microchannel plate intensifier design for use with a variety of demountable readout devices manufactured using standard multi-layer PCB techniques. We present results obtained using a 50 Ω multi-element design optimized for high speed operation and a four electrode multi-layer device developed from the wedge and strip anode with enhanced image resolution. The benefits of this intensifier design are discussed and a project to develop a detector system for bio-medical applications using a demountable readout device with integrated multi-channel ASIC-based electronics is announced.

Instrumentation for analysis and utilization of extreme-ultraviolet and soft x-ray high-order harmonics

The design and the performances of an extreme ultraviolet (EUV)spectrometer/monochromator for generation and diagnostics of high-order harmonics of an ultrashort (<30 fs) pulsed laser focused onto a gas jet are presented. The harmonic generation is optimized using an adaptive mirror before the laser focusing stage. A toroidal mirror is used to focus the XUV radiation in an intermediate stage for pump/probe experiments. A grazing-incidence flat-field spectrometer for the 5–75 nm spectral region has been designed: it adopts a stigmatic toroidal mirror and a varied line-space flat grating mounted in converging light. The almost flat stigmatic spectrum is acquired by a 40-mm-diameter microchannel plate intensifier; the whole detector can be moved to scan various portions of the spectrum. Different detectors allow one to acquire both integrated and single shot spectra at 1 kHz repetition rate. The absolute calibration of the spectrometer is provided. The same optical scheme can be applied to the design of a constant deviation angle EUV monochromator by substituting the detector block with an exit slit.

Optical design of a spectrometer-monochromator for the extreme-ultraviolet and soft-x-ray emission of high-order harmonics.

A grazing-incidence spectrometer-monochromator for diagnostics and application of the extreme-ultraviolet (EUV) and soft-x-ray high-order harmonics generated by the interaction between a few-optical-cycle laser pulse and a gas jet has been fabricated. We address the necessity of high-resolution spectral and spatial analyses of the high-order harmonics as well as their use as short EUV backlighters in pump-probe experiments. The spectrometer that we present uses a variable-line-spaced flat grating illuminated in the converging light coming from a toroidal mirror. The spectrum is stigmatic, and the focal surface is almost flat in a wide spectral region. The detector is a microchannel plate intensifier with a phosphor screen optically coupled to a CCD camera; it can be moved by means of a linear drive to acquire different portions of the spectrum in the 5-75-nm region. The resolution is almost limited by the pixel size of the detector. We apply the same optical scheme to achieve a constant-deviation-angle monochromator by substituting an exit slit for the detector block: The rotation of the grating gives the spectral scanning. A monochromator for the 5-50 nm spectral region is achieved.

High-order laser harmonics detection in the EUV and soft x-ray spectral regions

The design and performance of a spectroscopic instrument able to simultaneously measure spectral features, angular divergence, and conversion efficiency of high-order harmonics generated by an ultrashort pulsed laser focused onto a gas jet are presented. It combines an advanced optical setup with a EUV-sensitive bidimensional detector. The grazing-incidence spectrometer consists of two optical elements: a toroidal mirror and a spherical variable-line-spaced grating with flat-field properties. The mirror focuses the radiation tangentially on the grating entrance plane, in order to increase the flux collected by the grating. The grating has a variable groove spacing with parameters optimized to produce an almost flat focal surface in the 5–40 nm region. A 40 mm diameter microchannel plate intensifier is used to acquire the spectrum. The mirror does not compensate for the grating astigmatism, so the length of the spectral lines on the spectrum is proportional to the sagittal angular divergence of the high-order harmonic emission. The absolute response of the system was measured in order to obtain the conversion efficiency of the harmonic generation process. Some experimental examples reported here show very high sensitivity, which makes the system able to work in the single-shot operation, thus allowing us to follow the dynamic evolution of the harmonic generation process.

Grazing-incidence flat-field spectrometer for high-order harmonic diagnostics

The design and performances of an EUV spectrometer for diagnostics of high-order harmonics generated by an ultrashort (<30 fs) pulsed laser focused onto a gas jet are presented. The system consists of a toroidal mirror, an entrance slit, a spherical variable-line-spaced grating and a bidimensional detector. The mirror focuses astigmatically the radiation from the gas jet, with the tangential focus on the entrance slit. The grating diffracts the radiation coming out from the slit, spectrally focusing the 5 to 40 nm wavelength range in an almost straight focal curve, where the detector is located. The latter is a 40 mm diameter microchannel-plate intensifier. The spatial focal point of the toroidal mirror lies before the spectral focal plane of the spectrometer, so measurement of the height of the spectral lines gives the beam divergence. The spectral resolution of the spectrometer was measured using the narrow line spectra obtained by a microfocus soft x-ray source. Also the absolute response of the system, that is grating efficiency plus detector efficiency, was measured.

Comparison of charge coupled device vs film readouts for gated micro-channel plate cameras

We have used a large format (4000×4000) high resolution (9 μm pixels) charge coupled device (CCD) to record images from the rear of a gated micro-channel plate (MCP) intensifier, and compared the results with conventional film recording. Measurements of linearity, dynamic range, dark noise, and distortion all show that the CCD is a superior replacement for film. Furthermore, its excellent registration allows for easy flat fielding, using data from a uniformly exposed MCP. As we increase the signal level to where the signal to noise is not dominated by photon counting statistics, we find that this flat fielding procedure produces a significant improvement in signal to noise. The small spatial scale of this noise has led to its identification as high spatial frequency variations in the MCP phosphor.

Temporally and Spectrally Resolved Imaging Microscopy of Lanthanide Chelates

The combination of temporal and spectral resolution in fluorescence microscopy based on long-lived luminescent labels offers a dramatic increase in contrast and probe selectivity due to the suppression of scattered light and short-lived autofluorescence. We describe various configurations of a fluorescence microscope integrating spectral and microsecond temporal resolution with conventional digital imaging based on CCD cameras. The high-power, broad spectral distribution and microsecond time resolution provided by microsecond xenon flashlamps offers increased luminosity with recently developed fluorophores with lifetimes in the submicrosecond to microsecond range. On the detection side, a gated microchannel plate intensifier provides the required time resolution and amplification of the signal. Spectral resolution is achieved with a dual grating stigmatic spectrograph and has been applied to the analysis of luminescent markers of cytochemical specimens in situ and of very small volume elements in microchambers. The additional introduction of polarization optics enables the determination of emission polarization; this parameter reflects molecular orientation and rotational mobility and, consequently, the nature of the microenvironment. The dual spectral and temporal resolution modes of acquisition complemented by a posteriori image analysis gated on the spatial, spectral, and temporal dimensions lead to a very flexible and versatile tool. We have used a newly developed lanthanide chelate, Eu-DTPA-cs124, to demonstrate these capabilities. Such compounds are good labels for time-resolved imaging microscopy and for the estimation of molecular proximity in the microscope by fluorescence (luminescence) resonance energy transfer and of molecular rotation via fluorescence depolarization. We describe the spectral distribution, polarization states, and excited-state lifetimes of the lanthanide chelate crystals imaged in the microscope.

Uses of microchannel plate intensified detectors for imaging applications in the X-ray, EUV and visible wavelength regions

The Rutherford Appleton Laboratory Photon Counting Detector (RALPCD) has been refined to meet project requirements for a flexible imaging arrangement with applications at X-ray, EUV and visible wavelengths. The basic detector design comprises commercially available high gain microchannel plate intensifiers fibre optically coupled to CID or CCD cameras, to form a modular detector arrangement with the appropriate RAL detection and centroiding software. Frames of data from the cameras are detected and centroided in a Transputer or C40 parallel processor array where correction algorithms use look up tables to produce pattern free images at high resolution. Data from completed applications are used to illustrate the performance and future advances are discussed.

The effects of secondary electron emission on the operation of position sensitive anodes

Secondary electron emission plays a crucial role in the operation of position sensing anodes used in imaging microchannel plate (MCP) intensifiers. Secondary electrons emitted from the anode strongly influence both the size and shape of the collected charge cloud distribution and also mediate charge redistribution between the anode electrodes. The performance of position readouts using charge division can be severely limited by these mechanisms. We describe experiments designed to study the secondary electron emission process from a charge division position readout. An intermediate grid between the MCP and anode is used to establish an electric field above the anode to control the trajectories of the secondaries without disturbing the operation of the MCP. Tuning of the grid and anode voltages allows the measurement of a variety of physical processes occurring within the detector. We present measurements of the secondary emission coefficients of anode and grid materials, and show how both the initial spatial and energy distribution of primary electrons from the MCP may be measured. The usefulness of controlling secondary electrons to improve imaging performance is demonstrated.

Results from a 40 mm intensifier using a multilayer ceramic imaging element

We describe a highly versatile 40 mm diameter microchannel plate intensifier tube using an electronic image read out manufactured in a collaboration between the Mullard Space Science Laboratory and EEV. A development programme is underway to demonstrate photon imaging using a variety of charge division image read-out designs all of which are accommodated in a new generic tube design. Each read out is aimed for maximum performance at a specific region of the resolution versus dynamic range envelope, from high-speed, moderate resolution (10 MHz, 64 pixel) to ultimate resolution (100 kHz, 4000 pixel). The generic tube design utilizes a multilayer ceramic component which forms the tube vacuum vessel rear flange, while also acting as a 26 contact electrical feedthrough and as a substrate for the read-out anode. The output pins of the ceramic are arranged to mate with an industry-standard multipole socket for easy connection and replacement. This component provides a much more compact and robust solution to the integration of the electronic read out with the intensifier than is commonly seen with this technology. A further novel element in the design is a semi-transparent grid above the anode used to control secondary electron emission, an effect which can compromize imaging performance. We present results from initial testing of the device.

A position-sensitive detector mounted on an inner-shell electron energy-loss spectrometer

An inner-shell electron energy-loss spectrometer has been equipped with a position-sensitive multi-detector system consisting of two microchannel plate intensifiers, a phosphor screen and a charge-coupled device. This has led to a strong improvement in the data collection time which generally is fairly large for inner-shell transitions as the excitation cross sections are much smaller than those for valence-shell transitions. The SF6 electron energy-loss spectrum recorded at the S 2p edge with an energy resolution of 200 meV is given as an example.

Line spread function degradation in photon-counting detectors

An investigation of the degradation of the line spread function due to electron scattering in a micro-channel plate intensifier employing a semi-transparent photocathode and proximity focusing is reported. Data obtained using the Anglo-Australian Telescope (AAT) are used to measure emission line broadening and infilling of absorption features in astronomical spectra, due to scattering in the micro-channel plate intensifier. A comparison with a magnetically focused four-stage cascade intensifier is made. Values are obtained with the two intensifiers for equivalent width and residual infilling of a totally saturated absorption feature. The micro-channel plate intensifier is found to scatter into the wings of emission lines a larger fraction of the input signal than the cascade intensifier, amounting to 6.5% of the total signal. A model of the line spread function degradation observed in the micro-channel plate intensifier, based on electron scattering in the input proximity focused lens, is also presented. The modified line spread function obtained from this model is found to be a remarkably good fit to the data obtained at the AAT, and the values for infilling of absorption line features calculated from the model are close to those observed in the spectra. Finally, suggestions are made as to how the design of future micro-channel plate intensifiers can be modified to reduce scattering from the input micro-channel plate.

Pressure measurement by laser ionization: Direct counting of generated ions by imaging of their spatial distribution

The spatial distribution of ions generated by nonresonant multiphoton ionization of Xe and H2 with second harmonics of a picosecond YAG laser was imaged with a new detection system. Ions were observed as bright spots on a microchannel plate (MCP) intensifier, and they appeared on a straight line, reflecting the ion generation along a laser beam path. The size of the ionization region, which has a spindle shape, was estimated from the image. The maximum diameter of the ionization region was ∼60 μm, and the length was 3.6 mm for a Xe gas pressure of 5×10−5 Pa and an incident laser energy of 10 mJ/pulse for our measurement system. The size depended on the incident laser energy, and on the lens assembly used for the focusing of the laser beam. The possibility of relative pressure measurement by counting of the bright spot on the MCP intensifier was also investigated.

Two-dimensional intensified photodiode array detector for spaceflight use

A two-dimensional, ultraviolet photon-counting detector suitable for spaceflight use, consisting of a microchannel plate intensifier coupled to a Reticon photodiode array, has been constructed and tested. The design is an extension of the one-dimensional detector flown on the Hopkins Ultraviolet Telescope. Extensive laboratory measurements have determined the operating characteristics of the detector and shown that it can successfully centroid with subdiode resolution. It was flown as part of an ultraviolet spectrometer on two sounding rockets, and successfully obtained long slit spectra of Comet Austin (1990 V) and the Io plasma torus surrounding Jupiter in the wavelength range of 1150–1850 Å. Details of the design, construction, testing, and flight performance of the detector are presented.

2-D Light Diffraction from CCD and Intensified Reticon Multichannel Detectors Causes Spectrometer Stray Light Problems

Intensified diode arrays and charge-coupled detectors (CCD) which are used as multichannel detectors for spectroscopy exhibit strong 2-D diffraction of light due to the micro-channel plate intensifier and the CCD surface microelectronic structures. The strong 2-D diffraction of light by the intensified diode arrays shows hexagonal symmetry due to the hexagonal packing of the hollow glass fibers of the micro-channel plate intensifier. The 2-D diffraction of light from the CCD detectors shows square symmetry due to the almost square symmetry of the individual surface microelectronic structures. Light incident on the detector surfaces is diffracted into numerous angles which depend upon the incident angle and the light wavelength. This diffracted light can be redispersed and/ or reflected and scattered by optical elements inside the spectrometer. This diffracted light can then contribute to spectrometer diffuse stray light or it can be directly reimaged onto the detector to cause spectral artifacts. Backthinned CCD detectors do not show 2-D light diffraction and thus avoid these 2-D diffraction stray light limitations.