Fiber Optic Taper Research Articles

A CCD area detector for X-ray diffraction under high pressure for rotating anode source

Details of a two-dimensional X-ray area detector developed using a charge coupled device, a image intensifier and a fibre optic taper are given. The detector system is especially optimized for angle dispersive X-ray diffraction set up using rotating anode generator as X-ray source. The performance of this detector was tested by successfully carrying out powder X-ray diffraction measurements on various materials such as intermetallics AuIn2, AuGa2, high Z material Pd and low Z scatterer adamantane (C10H16) at ambient conditions. Its utility for quick detection of phase transitions at high pressures with diamond anvil cell is demonstrated by reproducing the known pressure induced structural transitions in RbI, KI and a new structural phase transition in AuGa2 above 10 GPa. Various softwares have also been developed to analyze data from this detector.

Multiple CCD detector for macromolecular X-ray crystallography

A charge-coupled device (CCD)-based detector designed for macromolecular crystallography is described. The detector has an area of 200 × 200 mm, a readout time of 1.6 s, and total noise equivalent to approximately three 12 keV X-ray photons per pixel. The detector is constructed from a 2 × 2 array of four identical units, each unit consisting of a 4.1:1 demagnifying fiber-optic taper bonded to a 1 k × 1 k, 24 µm pixel, CCD sensor. Each CCD is read out in parallel though four channels and digitized to 16 bits. A Gd2O2S phosphor X-ray-to-light converter bonded to an aluminized-plastic film is held in contact with the input surfaces of the fiber-optic tapers with an air pillow. The full width at half-maximum (FWHM) of the point response function is 120 µm, the response is linear to better than 1% over the entire range of intensity from background to nearly full well, the gain is 3.4 e per 8 keV incident X-ray photon, the noise is 12.6 e per pixel for a 10 s integration time, the modulation transfer function (MTF) is 0.35 at 5 line pairs (lp) mm−1(the Nyquest frequency), and the measured detective quantum efficiency (DQE) is 0.74 for relatively strong Bragg peaks. Data collected from crystallographic studies with synchrotron radiation are presented. In an anomalous difference Patterson map for a data set collected in 40 min on a monoclinic myoglobin crystal, the magnitude of the Fe–Fe peaks is 18 times the standard uncertainty of the map.

Analysis of the detective quantum efficiency of a developmental detector for digital mammography.

We are developing a modular detector for applications in full field digital mammography and for diagnostic breast imaging. The detector is based on a design that has been refined over the past decade for applications in x-ray crystallography [Kalata et al., Proc. SPIE 1345, 270-279 (1990); Phillips et al. ibid. 2009, 133-138 (1993), Phillips et al., Nucl. Instrum. Methods Phys. Rev. A 334, 621-630 (1993)]. The full field mammographic detector, currently undergoing clinical evaluation, is formed from a 19 cm x 28 cm phosphor screen, read out by a 2 x 3 array of butted charge-coupled device (CCD) modules. Each 2k x 2k CCD is optically coupled to the phosphor via a fiber optic taper with dimensions of 9.4 cm x 9.4cm at the phosphor. This paper describes the imaging performance of a two-module prototype, built using a similar design. In this paper we use cascaded linear systems analysis to develop a model for calculating the spatial frequency dependent noise power spectrum (NPS) and detective quantum efficiency (DQE) of the detector using the measured modulation transfer function (MTF). We compare results of the calculation with the measured NPS and DQE of the prototype. Calculated and measured DQEs are compared over a range of clinically relevant x-ray exposures and kVps. We find that for x-ray photon energies between 10 and 28 keV, the detector gain ranges between 2.5 and 3.7 CCD electrons per incident x-ray, or approximately 5-8 electrons per absorbed x ray. Using a Mo/Mo beam and acrylic phantom, over a detector entrance exposure range of approximately 10 to 80 mR, the volume under the measured 2-d NPS of the prototype detector is proportional to the x-ray exposure, indicating quantum limited performance. Substantial agreement between the calculated and measured values was obtained for the frequency and exposure dependent NPS and DQE over a range of tube voltage from 25 to 30 kVp.

High speed X-ray imaging camera using a structured CsI(Tl) scintillator

New third generation X-ray sources such as the Advanced Photon Source have created a need for a detector that can provide multiple frames of detailed X-ray images on the millisecond time scale. Such detectors will prove invaluable in applications such as time-resolved X-ray diffraction, X-ray microtomography, as well as materials science applications like polymer processing. Currently, detectors capable of acquiring high resolution X-ray images at such high speed do not exist, thus limiting progress in many of these important areas of research. To address these needs we have developed a prototype fast X-ray imaging system, using a structured CsI(Tl) scintillator coupled to a fast-frame 1 K/spl times/1 K CCD. The system has been successfully employed to capture 1024/spl times/64 pixel X-ray images at a rate of 1000 frames per second (fps) with a 12 bit dynamic range. The system exceeds the capabilities of the current high speed X-ray imaging systems which typically operate at the rate of 30 fps. Fabrication of a large area detector is currently underway, using a microstructured CsI(Tl) scintillator coupled to a fast-frame CCD with a 3:1 fiberoptic taper. The camera will operate in a burst mode, acquiring 8 1 K/spl times/1 K images at rates up to 1000 frames per second with 12 bit dynamic range. Higher image capture speeds can be accomplished by reducing the image area. This paper discusses the specific characteristics of the CsI(Tl) screens, experimental details of the prototype and the new design for the large area detector being developed specifically for time-resolved X-ray diffraction experiments in structural biology.

Charge-coupled device/fiber optic taper array x-ray detector for protein crystallography

A large area charge-coupled device (CCD) based fiber optic taper array detector (APS-1) is installed at the insertion-device beamline of the Structural Biology Center at the Argonne Advanced Photon Source x-ray synchrotron. The detector is used in protein crystallography diffraction experiments, where the objective is to measure the position and intensity of x-ray Bragg peaks in diffraction images. Large imaging area, very high spatial resolution, high x-ray sensitivity, good detective quantum efficiency, low noise, wide dynamic range, excellent stability and short readout time are all fundamental requirements in this application. The APS-1 detector converts the 2-D x-ray patterns to visible light images by a thin layer of x-ray sensitive phosphor. The phosphor coating is directly deposited on the large ends of nine fiber optic tapers arranged in a 3{times}3 array. Nine, thermoelectrically cooled 1024{times}1024pixel CCDs image the patterns, demagnified by the tapers. After geometrical and uniformity corrections, the nine areas give a continuous image of the detector face with virtually no gaps between the individual tapers. The 18 parallel analog signal-processing channels and analog-to-digital converters ensure short readout time and low readout noise. We discuss the design and measured performance of the detector. {copyright} {ital 1998 Society of Photo-Optical Instrumentationmore » Engineers.}{ital Key words:} charge-coupled device; fiber optic taper; x-ray diffraction; crystallography; imaging detector. {copyright} {ital 1998} {ital Society of Photo-Optical Instrumentation Engineers}« less

Noncontact single-fiber-optic proximity sensor using a laser-fabricated tap

We have developed a simple, noncontact, fiber-optic proximity sensor, using a laser micromachined tap on a single multimode optical fiber. The fiber end is placed near a target surface, and a beam of light is incident from the fiber onto the target. Some fraction of this light is reflected or scattered by the target and coupled back into the fiber. The amount recoupled into the fiber is dependent on the distance between the fiber end and the target surface as well as on other parameters such as the target's surface roughness. The fiber-optic tap allows us to monitor both the initial amount of light launched down the fiber toward the target and the amount of backreflected light from the target. For a known environment and target surface, variations in source intensity can be compensated for by monitoring the ratio of the two counterpropagating beams.

System considerations in CCD-based x-ray imaging for digital chest radiography and digital mammography.

System modeling is used to investigate the effect of various system parameters on the image quality in CCD-based x-ray imaging systems. The systems considered consist of a typical phosphor-based scintillating screen coupled to a CCD through lens or fiberoptic taper. Two applications, chest radiography and mammography, are analyzed. For each application typical system characteristics and operating conditions are used to determine the detective quantum efficiency (DQE) as a function of spatial frequency, optical collection efficiency, optical demagnification factor, and electronic noise. The DQE is modeled by extending the analysis for storage phosphor systems. The calculations are done for typical exposure conditions (0.25 mR for chest and 10.0 mR for mammography); however, the exposure effects are also discussed. It was found that a reasonable DQE can be obtained for both applications through each coupling approach; however, the demagnification requirements and electronic noise limitations are more stringent for the digital mammography application.

Coupling format variations in x-ray detectors based on charge coupled devices

Three variations of charge coupled device (CCD) based x-ray detectors have been constructed and evaluated, two of which are used for routine data collection on small angle x-ray diffraction beamlines at Princeton. The first detector consists of a commercially available CCD camera system lens coupled to the output of a four-stage magnetically focused image intensifier. The second system, assembled to gather test data, consists of a CCD fiber-optically coupled to an x-ray conversion phosphor via a 5:1 reduction fiber-optic taper. The final detector configuration was comprised of this fiber-optic taper system with the addition of a single stage proximity-focused image intensifier. Rationale is given for choosing components to be used in the assembly of CCD-based detectors.

High resolution X-ray sensor for non-destructive evaluation

Nondestructive evaluation (NDE) using X-rays is becoming indispensable for detecting microdefects in new materials currently used in aerospace and other engineering disciplines. Existing X-ray sensors pose limitations on the speed of operation due to persistence of the sensor and a problematic tradeoff between the sensor thickness and spatial resolution. To address these limitations we are developing a large area structured CsI(Tl) imaging sensor for NDE using CCD based radiographic and computed tomographic systems. The sensor is formed by vapor deposition of CsI(Tl) onto a specially designed fiber optic substrate. Our work has produced X-ray sensors with a factor of 4.5 greater light output, at least three orders of magnitude faster decay time response, and greater spatial resolution (16% modulation transfer function, MTF(f), at 14 line pairs per millimeter (1p/mm)) compared to the currently used high density Tb/sub 2/O/sub 3/ doped fiber optic glass scintillators. These performance advances will address the limitations of existing detector technology by producing high quality images and fast scan times required for real-time NDE inspection. Performance measurements for prototype CsI(Tl) scintillator converters are presented. With these new sensors the development of larger area fiber optic taper based CCD detectors with millisecond data acquisition capabilities and high spatial resolution suitable for NDE applications will be possible.

Analysis of signal propagation in optically coupled detectors for digital mammography: II. Lens and fibre optics

An x-ray detector for digital x-ray mammography is under investigation, which consists of a phosphor screen coupled by a demagnifying fibre-optic taper to a time-delay integration mode, charge-coupled device (CCD) image array. The signal propagation through such a detector depends on the intensity and angular emission of light from the phosphor screen, the angular acceptance and transmission of light through the optics, and the spectral sensitivity of the CCD to the fluorescent light. The production of light by the phosphor screen was considered in a previous paper. Here, the issues related to the optics are examined. For phosphor screens coupled by lenses with limiting acceptance angles of less than , it was calculated that the coupling efficiency would be 10% greater than would be estimated under the assumption of a Lambertian source. These increases occur because a phosphor screen typically produces light which is more forward directed than a Lambertian source. Similar increases in efficiency are observed when a phosphor screen is coupled to a fibre-optic faceplate or taper. For fibre optics, exact estimation of the optical coupling efficiency requires knowledge of the angular-dependent transmission efficiency of the fibres.

A Large-Format High-Resolution Area X-ray Detector Based on a Fiber-Optically Bonded Charge-Coupled Device (CCD)

An efficient two-dimensional X-ray detector based on direct imaging of an X-ray-sensitive phosphor with a high-resolution (1024 × 1024) charge-coupled device (CCD) array has been constructed and characterized. High detective quantum efficiency is obtained without an intensification stage through direct coupling of the phosphor to the CCD with a fiber-optic taper. The CCD is read out directly into computer memory, permitting X-ray images to be evaluated immediately after exposure without the need for a time-consuming scanning operation. The device has a large dynamic range, excellent spatial resolution and low noise characteristics, making it suitable both for macromolecular crystallography and for recording the weak diffuse signals encountered in small-angle diffraction experiments. Analysis of crystallography data taken at the Cornell High Energy Synchrotron Source gave Rsym values equal or superior to those of other recording media for several protein and virus crystals.

Macromolecular crystallographic results obtained at CHESS using a detector incorporating a charge‐coupled device

Results from various macromolecular crystallography experiments are presented showing the effectiveness of a recently installed detector incorporating a charge‐coupled device (CCD). This detector uses a 1024×1024 CCD directly coupled to an x‐ray sensitive phosphor by a fiber optic taper. The pixel size at the phosphor (50 μm) results in a point spread of 80 μm full width at half‐maximum. Even with the relatively small active area, 51×51 mm2, about 150 orders of diffraction can be resolved across the detector face. With this detector format, well‐resolved diffraction data have been collected from unit cells with edges as large as 360 A. In an offset configuration, the detector has been used to collect extremely high‐resolution data (1 A). A number of data sets have been collected having Rsym values in the 4%–6% range; in the case of room‐temperature lysozyme, an Rsym value as small as 2.1 was obtained for a 2.5 A resolution data set. In addition to fixed wavelength studies, the detector has also been used ...

Observer performance comparison of digital radiograph systems for stereotactic breast needle biopsy

Two digital radiograph systems for stereotactic mammography, one using a lens to couple a Lanex Regular screen to a back-illuminated charge-coupled device (CCD) and one using a fiber-optic taper to couple a Min-R Regular-type screen to a front-illuminated CCD, were evaluated with respect to observer performance. A contrast-detail phantom was imaged in a variety of equivalent exposure conditions on both systems. Six observers viewed images on a video monitor and recorded which objects were detected. Performance (percent correct detections) with the lens-coupled system using the Lanex Regular screen was significantly higher than with the fiber-optic-coupled system using the Min-R Regular-type screen. Differences in absorption efficiencies of phosphors used, as well as differences in design of the two cameras, can explain differences in observer detection performance.

A large area detector for X-ray applications

A large area detector for X-ray synchrotron applications has been developed. The front end of this device consists of a scintillator coupled to a fiber-optic taper. The fiber-optic taper is comprised of 4 smaller (70 mm × 70 mm) tapers fused together in a square matrix giving an active area of 140 mm × 140 mm. Each taper has a demagnification of 5.5 resulting in four small ends that are 12 mm diagonally across. The small ends of each taper are coupled to four microchannel-plate-based image intensifiers. The output from each image intensifier is focused onto a Charge Coupled Device (CCD) detector. The four CCDs are read out in parallel and are independently controlled. The image intensifiers also act as fast (20 ns) electronic shutters. The system is capable of displaying images in real time. Additionally, with independent control on the readout of each row of data from the CCD, the system is capable of performing high speed imaging through novel readout manipulation.

Characterization and data collection on a direct-coupled CCD X-ray detector

A large-area, multi-module, CCD-based detector without intensification stages is being developed by our group for X-ray diffraction applications. Each module consists of a fiberoptic taper with a phosphor deposited on the large end and a large-format, scientific CCD bonded to the small end. A single module has been constructed to evaluate the performance of this type of detector. This module has an active area of 43 × 43 mm 2, a point response function FWHM = 80 μm, a dynamic range of > 20 000:1, and a high DQE. Using four parallel readout circuits, the CCD can be read out in 1.8 s. Crystallographic data collected using a rotating-anode source demonstrate the capability of this type of detector.

Characterization of CCD-based imaging X-ray detectors for diffraction experiments

High-resolution CCD-based imaging detectors are successfully used in X-ray diffraction experiments. Some detectors are commercially available, others have been developed by research groups around the world. Reliable comparison of the performance must be based on thorough testing of all relevant characteristics of these detectors. We describe methods of measurements of detector parameters such as conversion gain, linearity, uniformity, point spread function, geometrical uniformity, dark current, and detective quantum efficiency. As an example for the characterization, test results of a single module fiberoptic taper/CCD X-ray detector will be presented. The projected performance of a large area, array detector consisting of 9 CCDs and fiberoptic taper modules, will be given. This new detector (the “Gold” detector) will be installed on Beamline X8C at the National Synchrotron Light Source at Brookhaven National Laboratory.

Fabrication of hybrid diffractive optics for fiber interconnects

The fabrication and performance of a hybrid diffractive optical system for use in planar optic interconnects is presented. Specifically, a novel fiber-optic tap utilizing both lithographic surface relief microlenses and interferometrically generated holographic volume elements is discussed. This system serves as an interface between fiber and planar optic interconnects for signal distribution. Design tradeoffs and experimental results are given. >

Area detector design Part II. Application to a modular CCD-based detector for X-ray crystallography

The performance of laboratory and synchrotron CCD-based detectors for X-ray crystallography is modeled using expressions which describe both the detector and the experiment. The detectors are constructed from an array of identical modules, each module consisting of a phosphor X-ray-to-light convertor, a fiberoptic taper and a CCD. The performance is characterized by the detective quantum efficiency (DQE) and dynamic range (DR), and by four additional expressions; the detective collective efficiency (DCE), experimental detective quantum efficiency (XDQE), experimental detective collection efficiency (XDCE) and experimental dynamic range (XDR). These additional expressions provide a means for including experimental constraints in the design of the detector. For a crystallography detector, these constraints include the requirements that the detector a) integrate Bragg peaks to maximum precision, and b) efficiently collect data to high resolution (large Bragg angle). Results obtained using these expressions demonstrate the need for a detector with a relatively large area. In order to build a such a detector from a reasonable number of modules using currently available fiberoptic tapers and CCDs, tapers with a demagnification ratio of > 3:1 are required. A different conclusion would be arrived at if the DQE alone were considered, demonstrating the importance of this method.

Programmable CCD imaging system for synchrotron radiation studies

A real-time imaging system for x-ray detection has been developed. The Computer Automated Measurement and Control (CAMAC)-based system has a charge coupled device (CCD) as its active detection element. The electronics consists of a CAMAC crate based dedicated microprocessor coupled to arbitrary wave form generators, programmable timing and analog-to-digital converter modules. The hardware flexibility achievable through this system enables us to use virtually any commercially available CCD. A dedicated CAMAC-based display driver allows for real-time imaging on a high-resolution color monitor. An optional front end consisting of a fibre-optic taper and a focusing optical lens system coupled to a phosphor screen allows for large area imaging. Further, programming flexibility, where the detector can be used in different readout modes, enables it to be exploited for time-resolved experiments. In one mode, sections of the CCD can be readout with millisecond time resolution and in another, the use of the CCD as a storage device is exploited resulting in microsecond time resolution. Three different CCDs with radically different readout timings and waveforms have been tested. The CCD characterized for uniformity, charge transfer efficiency, linearity and sensitivity is the TC215.

CCD-based detector for protein crystallography with synchrotron X-rays

A detector with a 114 mm aperture, based on a charge-coupled device (CCD), has been designed for X-ray diffraction studies in protein crystallography. The detector was tested at the National Synchrotron Light Source with a beam intensity, through a 0.3 mm collimator, of greater than 109 X-ray photons/s. A fiberoptic taper, an image intensifier, and a lens demagnify, intensify, and focus the image onto a CCD having 512×512 pixels. The statistical uncertainty in the detector output was evaluated as a function of conversion gain. From this, a detective quantum efficiency (DQE) of 0.36 was derived. The dynamic range of a 4×4 pixel resolution element, comparable in size to a diffraction peak, was 104. The point-spread function shows FWHM resolution of approximately 1 pixel, where a pixel is 160 μm on the detector face. A data set collected from a chicken egg-white lysozyme crystal, consisting of 495 0.1° frames, was processed by the MADNES data reduction program. The symmetry R-factors for the data were 3.2–3.5%. In a separate experiment a complete lysozyme data set consisting of 45 1° frames was obtained in just 36 s of X-ray exposure. Diffraction images from crystals of the myosin S1 head (a = 275 Å) were also recorded; the Bragg spots, only 5 pixels apart, were separated but not fully resolved. Changes in the detector design that will improve the DQE and spatial resolution are outlined. The overall performance showed that this type of detector is well suited for X-ray scattering investigations with synchrotron sources.