Multi Images Research Articles

High-gain image intensifier studies of electroluminescence in III–V semiconductors

A high-gain multistage image intensifier and microscope are used to study low-current dc electroluminescence in bulk semiconductors. A comparison is made with cathodoluminescence, and preliminary results for Ga1−xAlxAs and GaP are presented. It is shown how the technique gives information about the electrical contacts to a specimen, the electroluminescence spectra at points on a specimen, and the distribution of radiative recombination centers.

Use of a pulse image-amplifier uitramicroscope with a very high sensitivity in studies of inclusions in transparent condensed media

A Tyndall cone due to scattering inclusions in glass K–8 was observed using a pulse uitramicroscope with a ruby laser as the illumination source. The concentration of such inclusions was ~1011 cm−3 and their maximum size was ~2×10−5 cm. A modification of this uitramicroscope was developed on the basis of a multistage image amplifier used in combination with a photographic film to record the presence of inclusions. For an exposure of ≤10−3 sec, it should be possible to record (without a noise background) the presence of inclusions which scattered single photons. The main requirements that such a microscope would have to satisfy to ensure the maximum possible sensitivity were considered. This microscope should be useful in studies of the microstructure of optical materials and of the role of absorbing inclusions in the optical damage of dielectrics.

SINGLE PHOTOELECTRON EXCITATION OF PHOSPHORS

The statistical variation in the output intensity of single-stage image intensifiers has been measured under single photoelectron excitation. Early measurements on tubes with both P-ll and Ρ -20 phosphors indicated that the intensity distribution is not peaked but shows instead the maximum probability of occurrence for the smallest possible output intensities. These measurements, made on only two samples, were at variance with published results of similar measurements on multistage image intensifiers. Later measurements with improved statistics show a peaked distribution. The question is of fundamental importance in the implementation of systems that detect single photoelectron events in a two-dimensional image.

Sources of Multi-Electron Emission in Very Low Dark Cureit Image Intensifiers

High gain, multi-stage cascade image intensifiers with Sb (KNa) bi-alkali input photocathodes exhibit exceptionally low dark current. Because of the imaging properties of these tubes, the spatial distribution of dark current events, especially those involvirf instantaneous multielectron emission, can be investigated to yield information on the causes of dark current sources which are not related to the thermal conditions of the photocathode.

RECENT DEVELOPMENTS IN ULTRASONOGRAPHY

Developments in high resolution probes, data processing techniques and contrast means are providing a new generation of ultrasound technologies for diagnostic purposes. In this paper new results are presented derived from research performed at the Ultrasound Laboratory of the University of Florence. A new hardware and software platform called Fast Ecographic Multi Image Novel Apparatus (FEMMINA) has been developed based on innovative features. The radiofrequency signals, directly provided by the US transducers, contains fundamental information on the linear and non linear interaction of US with biological tissues. New suitable algorithms have been therefore developed to process on line such radiofrequency signals in order to identify and present information of clinical value. The main concept is the quantification of suitable parameters characterizing the morphology of the local frequency spectrum derived from a little volume of the biological tissue under investigation. Such parameters could be correlated to the microstructure tissue properties and are presented on the traditional tomographic map which are normally present in ultrasound instrumentation. The clinical validation of these techniques are illustrated pointing out the new perspectives for a more efficient and detailed analysis for selected pathologies.

Time delay in multistage image tubes

The temporal response of a single-stage image intensifier is characterized by the phosphor persistence, while that of a multistage unit is the convolution of the responses of the individual stages. This results in a greatly increased effective persistence, and a propagation delay of up to several milliseconds in commonly used three-stage image intensifiers.

Image Intensifiers and the Scotoscope

There exist at present several types of electronic image intensifiers, including the multistage intensifier image tube and the intensifier orthicon, which are useful for night vision. Furthermore, advances are being made in this class of device. High sensitivity in a low light level telescope or scotoscope requires that it employ a large diameter objective and an intensifier with a large cathode having high quantum efficiency.

Variable magnification operation of cascaded image tubes

A method of operating a multistage image tube with electron-optical demagnification in the first stage is described. A demagnification ratio of about 2 : 1 appeared to be the greatest factor attainable with the present arrangement, but it is concluded that the ratio could be increased by more precise determination of the electric field. The demagnification can be made continuousiy variable over a considerable range. (A.G.W.)

Performance of Multistage Image Amplifying Tubes; Astronomical Applications; and Proposed Use with Fabry-Perot Etalons for Stellar Spectroscopy.

view Abstract Citations (2) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Performance of Multistage Image Amplifying Tubes; Astronomical Applications; and Proposed Use with Fabry-Perot Etalons for Stellar Spectroscopy. Dunham, T., Jr. Abstract and Weekly, B., Nature 185, 370, 1960) offer advantages for photometry at low flux levels: (1) high- speed recording; (2) background electrons are focused at the output, thereby reducing the number per resolution band to approximately 10-~ of the contribution encountered with photomultipliers; and (3) scintillations, corresponding to individual photoelectrons, are bright enough to permit recording a considerable fraction on moving film. Information storage is greater on moving film and scintillations in individual spectral resolution bands can be counted, so that the tubes can be used as multi- channel pulse counters [Dunham, T., Jr., J. Opt. Soc. Am. 50, 1129(A), 19601. The factor of merit of an image tube for spectrophotometry may be expressed as G2r2/N, where G is the over-all light gain, r the linear resolution, and N the background. For direct stellar photometry, an image tube offers the possibility of recording flux from a number of star images (and sky) simultaneously, using fiber light guides to transfer images to a linear array on the photocathode, so that scintillations can be recorded and counted on moving film. Speed, resolution, and background have been investigated, using test spectra and coude' spectra with Baum's microprojector (Baum, W. A., Advances in Electronics and Electron. Phys. 16, 391, 1962). The percentage of incident photons that can be recorded on film has been determined by using a low-intensity scattering source of approximately monochromatic light. For high-resolution spectroscopy, the use of an image tube and moving film, with a scanning FabryPerot etalon (Jacquinot, P., and Dufour, C., J. Reck., Cent. Nat. Rech. Sci. 2, 19,1948) and rotating grating, appears to offer an efficient system that permits pulse counting of many fringes simultaneously. For space spectroscopy, direct electrical pickup at the output, on narrow conducting strips corresponding to the fringes, and connected to individual pulsecounting circuits, would have advantages. The experimental part of this study was carried out at Imperial College, thanks to the kindness of Dr. J. D. McGee. Publication: The Astronomical Journal Pub Date: June 1962 DOI: 10.1086/108872 Bibcode: 1962AJ.....67R.575D full text sources ADS |

Image Intensification by Transmission Secondary Electron Emission

The successful operation of a multistage image intensifier using a series of aluminum dynodes coated with thin layers of BaF/sub 2/ and reinforced with very fine wide-mesh grid ia reported. The electron gain in the best of these tubes is 2400, corresponding to sn average secondary emission ratio of 7 per dynode. The photon gsin with 15kw acceleration from the last dynode to a P11 output phosphor is about 10,000. At low light levels, resolution is limited by photoelectron noise. This tube, when fully developed, will be well suited to the amplification of extremely low light level images such as those encountered in astronomy, nuclear particle track photography, spectroscopy, and x-ray fluoroscopy. (D.L.C.)