Charge Injection Device Camera Research Articles

Optical emission sensing for laser-based additive manufacturing—What are we actually measuring?

Numerous sensing modalities have been utilized to monitor metal additive manufacturing, thus assessing process stability and build quality. One common directed energy deposition sensing method is coaxial “melt pool” imaging, wherein a camera mounted coaxially with the laser-focusing optics views the laser-interaction zone via a dichroic mirror. This work demonstrates that coaxial “melt pool” imaging does not always provide reliable, as-solidified, pool geometry measurements. First, coaxially acquired images captured using a charge injection device camera for a range of laser powers, translation speeds, and powder flow rates are compared to optical profilometry-measured true deposition geometries. Furthermore, coaxial “melt pool” images and plume geometries, measured using a bandpass filtered CCD camera, show significant, abrupt “melt pool” geometry changes, which correspond to plume geometry changes. Additionally, interbuild comparisons demonstrate a linear relationship between “melt pool” and plume geometry. The authors conclude that coaxial imaging, as commonly implemented, is an often unreliable melt pool geometry measurement because plume emissions in and around the laser-interaction zone may obscure the melt pool.

Calibration of X-ray imaging devices for accurate intensity measurement

National Security Technologies (NSTec) has developed calibration procedures for X-ray imaging systems. The X-ray sources that are used for calibration are both diode type and diode/fluorescer combinations. Calibrating the X-ray detectors is a key to accurate calibration of the X-ray sources. Both energy dispersive detectors and photodiodes measuring total flux were used. We have developed calibration techniques for the detectors using radioactive sources that are traceable to the National Institute of Standards and Technology (NIST). The German synchrotron at Physikalische Technische Bundestalt (PTB) was used to calibrate the silicon photodiodes over the energy range from 50 to 60 keV. The measurements on X-ray cameras made using the NSTec X-ray sources included quantum efficiency averaged over all pixels, camera counts per photon per pixel, and response variation across the sensor. The instrumentation required to accomplish the calibrations is described. The X-ray energies ranged from 720 to 22.7 keV. The X-ray sources produce narrow energy bands, allowing us to determine the properties as a function of X-ray energy. The calibrations were done for several types of imaging devices. There were back and front illuminated CCD (charge-coupled device) sensors, and a CID (charge injection device) type camera. The CCD and CID camera types differ significantly in some of their properties that affect the accuracy of the X-ray intensity measurements. All the cameras discussed here are silicon based. The measurements of the quantum efficiency variation with the X-ray energy are compared to the models for the sensor structure. The cameras that are not back-thinned are compared to those that are.

同期画像入力による微小繰返し変位の検出法

An object shape is changed by cyclic physical excitements, for example, sunlight in nature or vibration in factory. The change of shape is very fine and also cyclic. A new method is given for detecting edge movements of a cyclic moved object by cyclic physical excitements. The movement is very fine in a pixel on the image sensing device in a CID (Charge Injection Device) camera, but can be sensed by synchronized image input as cyclic edge movements of object. Every cycle has two images. One is with the excitement and another is with no excitement. The difference between the two images is calculated and these differences are summed 8 times. The summation has 64X128 matrix and shows the edge movement of a moved object. A conventional method with asynchronized image input gives 0.1 pixel resolution. The new method with synchronized image input gives 0.036 pixel resolution.

Imaging neutron beams with scintillating fiber faceplates

An imaging system for neutron beams based on scintillating fiber faceplates is described. The scintillating fibers are made from lithium silicate glass doped with Ce 3+ using isotopically enriched 6Li. Several faceplates ranging in thickness from 1.3 to 3.2 mm have been tested using a position-sensitive photomultiplier or a Charge Injection Device camera as the photodetector. Advantages of scintillating fiber faceplates include high neutron capture efficiency, good position resolution, and the possibility of low-cost, large-area detectors.

Charge Injection Device (CID) technology — A solution for photon and particle imaging applications

Charge Injection Device (CID) imagers provide key electro-optical performance features and versatile readout capabilities for spatial and radiometric measurements of photon and particle radiation. CIDs have many of the performance features required for machine vision and scientific applications including good resolution, broad spectral response, resistance to blooming and asynchronous operation for feature detection and measurement. Single pixel imaging devices and two-dimensional arrays possess exceptionally large pixel charge capacities and wide dynamic range that provide quantum (shot-noise) limited operation. Commercial devices have demonstrated the robustness and capability to operate in hostile (including ionizing radiation) environments. Recently-developed CID imagers and camera systems have incorporated new on-chip architectures and process technology that provide low-noise performance and permit exploitation of additional features including random-pixel addressability, true non-destructive pixel readout (NDRO), and two-dimensional windowing (subarray readout). These CID features allow scientists to monitor and adapt application exposure in real time, reduce noise, and read out small pixel subarrays at fast rates. CID imagers possess structural characteristics and improved radiation tolerance (∼ 10 6 gamma) which allow these devices to operate in harsh radioactive environments and image different forms of radiation including X-rays, electron beams and nuclear radiation.

Visible spectroscopy on the Tokamak de Varennes with high spatial resolution

A vertical slice of a tokamak plasma is imaged onto the entrance slit of a spectrometer, giving at the exit plane both the spectral (horizontal axis) and the spatial (vertical axis) distributions of the collected light. An intensified CID (charge injection device) camera is mounted at the exit plane to record the spatially and spectrally resolved emission profiles of low-Z impurities, with a temporal resolution of 1/60 s. The large number of lines of sight allows for inversion of chord-integrated signals to obtain local emissivities. Profiles from several ionization stages of carbon and oxygen are compared to the predictions of the impurity transport code MIST (multi-ionized species transport) to deduce impurity diffusion coefficients.

Performance characteristics of a real-time digital x-ray fluoroscopic system using an intensified charge injection device camera and CsI:Na crystal.

A digital x-ray photoelectronic imaging system has been constructed using an optically flat 152-mm-diam, 2.5-mm-thick CsI:Na scintillating crystal. X-ray images formed by the scintillator are viewed by a single microchannel plate intensified charge injection device (ICID) camera and digitized at a real-time rate by a computerized frame-grabbing system. Video images are recorded and selected image frames are subjected to image processing and analysis schemes. Parameters governing the performance characteristics of the system are determined accordingly. For a 152-mm field size at the crystal plane, a spatial resolution limit of 1.50 +/- 0.10 1p/mm (1 sigma) measured at the 4% level of the modulation transfer function of the system has been obtained. This result is consistent with the measurements of the full width at half-maximum of the line spread function which is found to be 645 +/- 35 microns (1 sigma). Similarly, the intrinsic resolution of the CsI:Na scintillator only was found to be 6.5 +/- 0.5 1p/mm (1 sigma). Contrast ratio measurements, which are mainly determined by the quality of phosphor, have indicated a value of 12.1 +/- 0.6, whereas minimum visible details are observed at radiation exposure rates of 100 microR/s. This limit has been reduced to 10 microR/s using the single-scan integrating option provided by the ICID camera. A maximum contrast resolution of 1% corresponding to 100 statistically significant meaningful gray levels is achieved at a maximum exposure rate of 1000 microR/s. Consequently, although the imaging capability of the present system compares favorably with that of conventional x-ray video-fluoroscopic systems, a better performance may be achieved by using a higher resolution cooled dual-microchannel intensified CID camera in conjunction with a thinner CsI:Na crystal and a real-time digital image processing subsystem.

Scintillator-fiber charged-particle track-imaging detector

A scintillator-fiber charged-particle track-imaging detector has been developed using a bundle of square cross section plastic scintillator fiber optics, proximity focused onto an image intensified Charge Injection Device (CID) camera. The tracks of charged particles penetrating into the scintillator fiber bundle are projected onto the CID camera and the imaging information is read out in video format. We have exposed our detector to beams of 15 MeV protons and relativistic neon, manganese, and gold nuclei and have obtained images of their tracks. This paper presents details of the detector technique, properties of the tracks obtained, and preliminary range measurements of 15 MeV protons stopping in the fiber bundle.