In the plasma flash x-ray generator, a 200 nF condenser is charged up to 50 kV by a power supply, and flash x-rays are
produced by the discharging. The x-ray tube is a demountable triode with a trigger electrode, and the turbomolecular
pump evacuates air from the tube with a pressure of approximately 1 mPa. Target evaporation leads to the formation of
weakly ionized linear plasma, consisting of ferrum ions and electrons, around the fine target, and intense K-series
characteristic x-rays are produced from the plasma axial direction. At a charging voltage of 50 kV, the maximum tube
voltage was almost equal to the charging voltage of the main condenser, and the peak current was about 15 kA. In the
spectral measurement, Kβ rays were intense, and higher harmonic x-rays were observed. The pulse widths were 0.5 μs,
and the maximum x-ray intensity was approximately 300 μGy.
The noise of today's CCD-cameras can be so small that the photon's shot noise is dominant. The size of possible
grey steps is calculated. It depends on the intensity of light. If the picture has 100 grey steps, then the high of the
detectable grey step is about 100times as large in the bright part of the picture compared with the smallest steps
in the dark part of the image. The results are applied to experiments. The picture quality is discussed in relation
to resolution in space and time. A parallelepiped block for images is presented. If you want to have a delicately
stepped grey scale, then you have to drop other information which is carried by the photons.
We show bubbles investigated with videography and multiple colour LED flash illumination. The short flashes show the propagation and development of the shape of the bubbles. The long flashes make the velocity vector of the bubbles directly visible and allow easy investigation of the unstable movement. If bubbles are used to reduce friction of ships, then it is effective to spread the gas volume over lots of micro bubbles. Another experiment is the investigation of the noise of a bass reflex loud-speaker. The visualisation of air flow shows linear behaviour at low power and a previously unknown effect at high power - continuous streaming of air in the bass reflex tube.
The discharge in linear plasma X-ray flash tubes ( Sato tubes ) is simulated. For the geometry of a cylinder cathode outside and an anode in the centre, the electrical fields and potentials are calculated and the propagation of electrons are studied. Space charge limits the current in the initial phase strongly. Replacing the vacuum by plasma from the anode evaporation, it is possible to get increasing current and strong X-ray pulses. Space charge is important for the high intensity X-ray production up to the end of the emission.
In the plasma flash x-ray generator, a 200 nF condenser is charged up to 50 kV by a power supply, and flash x-rays are
produced by the discharging. The x-ray tube is a demountable triode with a trigger electrode, and the turbomolecular
pump evacuates air from the tube with a pressure of approximately 1 mPa. Target evaporation leads to the formation of
weakly ionized linear plasma, consisting of molybdenum ions and electrons, around the fine target. At a charging
voltage of 50 kV, the maximum tube voltage was almost equal to the charging voltage of the main condenser, and the
peak current was about 17 kA. The K-series characteristic x-rays were clean and intense, and higher harmonic x-rays
were not observed. The x-ray pulse widths were approximately 600 ns, and the time-integrated x-ray intensity had a
value of approximately 2.0 mGy per pulse at 1.0 m from the x-ray source with a charging voltage of 50 kV.
The gadolinium plasma flash x-ray generator is useful for performing high-speed enhanced K-edge angiography using
cone beams because K-series characteristic x-rays from the gadolinium target are absorbed effectively by iodine-based
contrast media. In the flash x-ray generator, a 150 nF condenser is charged up to 80 kV by a power supply, and flash
x-rays are produced by the discharging. The x-ray tube is a demountable cold-cathode diode, and the turbomolecular
pump evacuates air from the tube with a pressure of approximately 1 mPa. Since the electric circuit of the high-voltage
pulse generator employs a cable transmission line, the high-voltage pulse generator produces twice the potential of the
condenser charging voltage. At a charging voltage of 80 kV, the estimated maximum tube voltage and current are
approximately 160 kV and 40 kA, respectively. When the charging voltage was increased, the K-series characteristic
x-ray intensities of gadolinium increased. Bremsstrahlung x-ray intensity rate decreased with increasing the charging
voltage, and clean K lines were produced with a charging voltage of 80 kV. The x-ray pulse widths were
approximately 100 ns, and the time-integrated x-ray intensity had a value of approximately 500 μGy at 1.0 m from the
x-ray source with a charging voltage of 80 kV. Angiography was performed using a filmless computed radiography
(CR) system and iodine-based contrast media. In the angiography of nonliving animals, we observed fine blood
vessels of approximately 100 μm with high contrasts.
Novel monochromatic x-ray generators and their applications to high-speed radiography are described. The five
generators are as follows: a weakly ionized linear plasma x-ray generator, a monochromatic compact flash x-ray
generator, a super-fluorescent plasma generator, a cerium x-ray generator using a 3.0-mm-thick aluminum filter, and a
100micron-focus x-ray generator utilizing the filter. Using the linear plasma generator with a copper target, we observed
clean K lines and their harmonics, and soft flash radiography was performed with pulse widths of approximately 500
ns. The compact monochromatic flash x-ray generator produced clean molybdenum K lines easily, and high-speed
radiography was performed with pulse widths of approximately 100 ns. Using a steady-state cerium x-ray generator,
we performed real-time angiography utilizing an image intensifier and a high-sensitive camera (MLX) made by NAC
Image Technology Inc. with a capture time of 1 ms. Finally, real-time magnification radiography was performed by
twofold magnification imaging using a 100micron-focus x-ray generator and the high-sensitive camera.
In the plasma flash x-ray generator, a 200 nF condenser is charged up to 50 kV by a power supply, and flash x-rays are produced by the discharging. The x-ray tube is a demountable triode with a trigger electrode, and the turbomolecular pump evacuates air from the tube with a pressure of approximately 1 mPa. Target evaporation leads to the formation of weakly ionized linear plasma, consisting of copper ions and electrons, around the fine target, and intense Kα lines are left using a 10-μm-thick nickel filter. At a charging voltage of 50 kV, the maximum tube voltage was almost equal to the charging voltage of the main condenser, and the peak current was about 16 kA. The K-series characteristic x-rays were clean and intense, and higher harmonic x-rays were observed. The x-ray pulse widths were approximately 300 ns, and the time-integrated x-ray intensity had a value of approximately 1.5 mGy per pulse at 1.0 m from the x-ray source with a charging voltage of 50 kV.
The tungsten plasma flash x-ray generator is useful in order to perform high-speed enhanced K-edge angiography using cone beams because Kα rays from the tungsten target are absorbed effectively by gadolinium-based contrast media. In the flash x-ray generator, a 150 nF condenser is charged up to 80 kV by a power supply, and flash x-rays are produced by the discharging. The x-ray tube is a demountable diode, and the turbomolecular pump evacuates air from the tube with a pressure of approximately 1 mPa. Since the electric circuit of the high-voltage pulse generator employs a cable transmission line, the high-voltage pulse generator produces twice the potential of the condenser charging voltage. At a charging voltage of 80 kV, the estimated maximum tube voltage and current were approximately 160 kV and 40 kA, respectively. When the charging voltage was increased, the characteristic x-ray intensities of tungsten Kα lines increased. Using an ytterbium oxide filter, the Kα lines were clean, and hardly any Kβ lines and bremsstrahlung rays were detected. The x-ray pulse widths were approximately 60 ns, and the time-integrated x-ray intensity had a value of approximately 50 μGy at 1.0 m from the x-ray source with a charging voltage of 80 kV. Angiography was performed using a film-less computed radiography system and gadolinium-based contrast media. In angiography of non-living animals, we observed fine blood vessels of approximately 100 μm with high contrasts.
Energy-selective high-speed radiography utilizing a kilohertz-range stroboscopic x-ray generator and its application to high-speed angiography are described. This generator consists of the following major components: a main controller, a condenser unit with a Cockcroft-Walton circuit, and an x-ray tube unit in conjunction with a grid controller. The main condenser of about 500 nF in the unit is charged up to 120 kV by the circuit, and the electric charges in the condenser are discharged to the triode by the grid control circuit. Although the tube voltage decreased during the discharging for generating x-rays, the maximum value was equal to the initial charging voltage of the main condenser. The maximum tube current and the repetition rate were approximately 0.5 A and 50 kHz, respectively. The x-ray pulse width ranged from 0.01 to 1.0 ms, and the maximum shot number had a value of 32. At a charging voltage of 100 kV and a width of 1.0 ms, the x-ray intensity obtained using a 50-μm-thick tungsten filter was 9.88 μGy at 1.0 m, and the dimensions of the focal spot had values of approximately 1×1 mm. Angiography was performed using the filter at a charging voltage of 100 kV.
The high-voltage condensers in a polarity-inversion two-stage Marx surge generator are charged from –50 to –70 kV by a power supply, and the electric charges in the condensers are discharged to an x-ray tube after closing gap switches in the surge generator with a trigger device. The x-ray tube is a demountable diode, and the turbomolecular pump evacuates air from the tube with a pressure of approximately 1 mPa. Clean silver K lines are produced using a 30-µm-thick palladium filter, since the tube utilizes a disk cathode and a rod target, and bremsstrahlung rays are not emitted in the opposite direction to that of electron acceleration. At a charging voltage of –70 kV, the instantaneous tube voltage and current are 90 kV and 0.8 kA, respectively. The x-ray pulse widths are approximately 80 ns, and the instantaneous number of generator-produced K photons is approximately 4×107photons/cm2 per pulse at 0.3 m from the source 3.0 mm in diameter.
High-voltage condensers in a polarity-inversion two-stage Marx surge generator are charged from -50 to -70 kV using a power supply, and the electric charges in the condensers are discharged to an x-ray tube after closing the gap switches in the surge generator using a trigger device. The x-ray tube is a demountable diode, and the turbomolecular pump evacuates air from the tube with a pressure of approximately 1 mPa. Clean copper Kα lines are produced using a 10-μm-thick nickel filter, since the tube utilizes a disk cathode and a rod target, and bremsstrahlung rays are not emitted in the opposite direction to that of electron acceleration. The peak tube voltage increased with increasing charging voltage. At a charging voltage of -70 kV, the peak tube voltage and current were 140 kV and 0.8 kA, respectively. The pulse widths were approximately 30 ns, and the maximum dimension of the x-ray source was 3.0 mm in diameter. The number of generator-produced Kα photons was approximately 2.5x106 photons/cm2 at 0.5 m per pulse.
In the plasma flash x-ray generator, a 200 nF condenser is charged up to 50 kV by a power supply, and flash x rays are produced by the discharging. The x-ray tube is a demountable triode with a trigger electrode, and the turbomolecular pump evacuates air from the tube with a pressure of approximately 1 mPa. Target evaporation leads to the formation of weakly ionized linear plasma, consisting of molybdenum ions and electrons, around the fine target, and intense characteristic x rays are produced. At a charging voltage of 50 kV, the maximum tube voltage was almost equal to the charging voltage of the main condenser, and the peak current was about 16 kA. When the charging voltage was increased, the linear plasma formed, and the K-series characteristic x-ray intensities increased. The K lines were quite sharp and intense. The x-ray pulse widths were approximately 600 ns, and the time-integrated x-ray intensity had a value of approximately 65 μC/kg at 1.0 m from the x-ray source with a charging voltage of 50 kV.
The high-voltage condensers in a polarity-inversion two-stage Marx surge generator are charged from -50 to -70 kV by a power supply, and the electric charges in the condensers are discharged to an x-ray tube after closing gap switches in the surge generator with a trigger device. The x-ray tube is a demountable diode, and the turbomolecular pump evacuates air from the tube with a pressure of approximately 1 mPa. Tungsten characteristic x rays can be produced, since the tube utilizes a disk cathode and a rod target, and bremsstrahlung rays are not emitted in the opposite direction to that of electron acceleration. At a charging voltage of -70 kV, the instantaneous tube voltage and current were 140 kV and 1.0 kA, respectively. The x-ray pulse widths were approximately 90 ns, and the estimated number of K photons was approximately 5×108 photons/cm2 per pulse at 0.5 m from the source of 3.0 mm in diameter.
The fundamental experiments for measuring soft x-ray characteristics from the vacuum capillary are described. These experiments are primarily performed in order to generate intense soft x rays. The generator consists of a high-voltage power supply, a polarity-inversion ignitron pulse generator, a turbomolecular pump, and a radiation tube with a capillary. A high-voltage condenser of 200 nF in the pulse generator is charged up to 20 kV by the power supply, and the electric charges in the condenser are discharged to the capillary in the tube after closing the ignitron. During the discharge, weakly ionized plasma forms on the inner and outer sides of a capillary. In the present work, the pump evacuates air from the tube with a pressure of about 1 mPa, and a demountable capillary was developed in order to measure x-ray spectra according to changes in the capillary length. In this capillary, the anode (target) and cathode elements can be changed corresponding to the objectives. The capillary diameter is 2.0 mm, and the length is adjusted from 1 to 50 mm. When a capillary with aluminum anode and cathode electrodes was employed, both the cathode voltage and the discharge current almost displayed damped oscillations. The peak values of the voltage and current increased when the charging voltage was increased, and their maximum values were -11.5 kV and 4.7 kA, respectively. The x-ray durations observed by a 1.6 μm aluminum filter were less than 30 μs. In the spectrum measurement, we observed orderly multi-line spectra. The line photon energies seldom varied according to changes in the condenser charging voltage and to changes in the electrode element. The line number decreased with corresponding decreases in the capillary length.
The cerium target plasma flash x-ray generator is useful in order to perform high-speed enhanced K-edge angiography using cone beams because K-series characteristic x rays from the cerium target are absorbed effectively by iodine-based contrast mediums. In the flash x-ray generator, a 150 nF condenser is charged up to 80 kV by a power supply, and flash x rays are produced by the discharging. The x-ray tube is a demountable diode, and the turbomolecular pump evacuates air from the tube with a pressure of approximately 1 mPa. Since the electric circuit of the high-voltage pulse generator employs a cable transmission line, the high-voltage pulse generator produces twice the potential of the condenser charging voltage. At a charging voltage of 80 kV, the estimated maximum tube voltage and current were approximately 160 kV and 40 kA, respectively. When the charging voltage was increased, the K-series characteristic x-ray intensities of cerium increased. The K lines were clean and intense, and hardly any bremsstrahlung rays were detected at all. The x-ray pulse widths were approximately 100 ns, and the time-integrated x-ray intensity had a value of approximately 10 μC/kg at 1.0 m from the x-ray source with a charging voltage of 80 kV. In the angiography, we employed a film-less computed radiography (CR) system and iodine-based microspheres.
If a coaxial cable or a strip line has an open end, then the incoming signal is reflected there. Due to the propagation velocity, an incoming rectangular pulse has a length in space which depends on its length in time. If the pulse length is twice the cable length, then after the reflection at the end, the pulse energy is distributed in an electrical field along the cable. Input and output current are compensating. At this time, it is possible to take out the energy simultanously through several switched connections at the same time. The result is a shorter pulse of much higher power which can drive a load of low impedance or with the pulse transformer presented at the 25th ICHSPP give a short pulse of very high voltage. This concentration in time of the electrical energy is planed to be used for x-ray flash systems. If the input pulse is not rectangular, then it is possible to take off the energy at the time of best peak power.
Bei einem Bandleiter oder Koaxialkabel mit offenem Ende wird das auf der Leitung laufende Signal reflektiert. Die Ausdehnung eines Rechteckimpulses auf einer solchen Leitung entspricht seiner Dauer und der Ausbreitungsgeschwindigkeit auf der Leitung. Wenn die Impulsausdehnung doppelt so gross ist wie die Leitungslange, dann kann die gesamte Energie des Impulses nach der Reflexion im elektrischen Feld gespeichert sein, Eingangs und Reflexionsstrom kompensieren sich. Zu dieser Zeit ist es moglich, fast die ganze Energie gleichzeitig seitlich durch einen ausgedehnten oder mit mehreren einzelnen Schaltern an einen niederohmigen Verbraucher weiterzuleiten oder mit einem Impulstransformator ( gezeigt auf dem 25. ICHSPP ) an dessen Impedanz anzupassen. Der Ausgangsimpuls ist sehr kurz und von vervielfachter Leistung. Diese zeitliche Energiekonzentration soll spater fur Rontgenbltzsysteme verwendet werden. Im Falle eines nicht rechteckformigen Eingangsimpulses kann die Energie wahrend der hochsten Spitzenleistung entnommen werden.
The high-voltage condensers in a polarity-inversion two-stage Marx surge generator are charged from -50 to -70 kV by a power supply, and the electric charges in the condensers are discharged to an x-ray tube after closing gap switches in the surge generator with a trigger device. The x-ray tube is a demountable diode, and the turbomolecular pump evacuates air from the tube with a pressure of approximately 1 mPa. Clean silver Kα lines are produced using a 30 μm-thick palladium filter, since the tube utilizes a disk cathode and a rod target, and bremsstrahlung rays are not emitted in the opposite direction to that of electron acceleration. At a charging voltage of -70 kV, the instantaneous tube voltage and current were 90 kV and 0.8 kA, respectively. The x-ray pulse widths were approximately 80 ns, and the instantaneous number of generator-produced Kα photons was approximately 40 M photons/cm2 per pulse at 0.3 m from the source of 3.0 mm in diameter.
In the plasma flash x-ray generator, high-voltage main condenser of about 200 nF is charged up to 55 kV by a power supply, and electric charges in the condenser are discharged to an x-ray tube after triggering the cathode electrode. The flash x-rays are then produced. The x-ray tube is of a demountable triode that is connected to a turbo molecular pump with a pressure of approximately 1 mPa. As electron flows from the cathode electrode are roughly converged to a rod cerium target of 3.0 mm in diameter by electric field in the x-ray tube, the weakly ionized linear plasma, which consists of cerium ions and electrons, forms by target evaporating. At a charging voltage of 55 kV, the maximum tube voltage was almost equal to the charging voltage of the main condenser, and the peak current was
about 20 kA. When the charging voltage was increased, weakly ionized cerium plasma formed, and the K-series characteristic x-ray intensities increased. The x-ray pulse widths were about 500 ns, and the time-integrated x-ray intensity had a value of about 40 μC/kg at 1.0 m from x-ray source with a charging voltage of 55 kV. In the
angiography, we employed a film-less computed radiography (CR) system and iodine-based microspheres. Because K-series characteristic x-rays are absorbed easily by the microspheres, high-contrast angiography has been performed.
In the plasma flash x-ray generator, a high-voltage main condenser of approximately 200 nF is charged up to 50 kV by a power supply, and electric charges in the condenser are discharged to an x-ray tube after triggering the cathode electrode. The flash x-rays are then produced. The x-ray tube is a demountable triode that is connected to a turbo molecular pump with a pressure of approximately 1 mPa. As electron flows from the cathode electrode are roughly converged to a rod copper target of 3.0 mm in diameter by the electric field in the x-ray tube, weakly ionized linear plasma, which consists of copper ions and electrons, forms by target evaporation. At a charging voltage of 50 kV, the maximum tube voltage was almost equal to the charging voltage of the main condenser, and the peak current was about 15 kA. When the charging voltage was increased, the linear plasma formed, and the K-series characteristic x-ray intensities increased. The K-series lines were quite sharp and intense, and hardly any bremsstrahlung rays were detected. The x-ray pulse widths were approximately 700 ns, and the time-integrated x-ray intensity had a value of approximately 30 μC/kg at 1.0 m from the x-ray source with a charging voltage of 50 kV.
Quasi-monochromatic parallel flash radiography system utilizing a plane-focus plasma x-ray tube in conjunction with an x-ray lens is described. The x-ray generator employs a high-voltage power supply, a low-impedance coaxial transmission line, a high-voltage condenser with a capacity of about 200 nF, a turbo-molecular pump, a krytron pulse generator as a trigger device, and a flash x-ray tube. The high-voltage main condenser is charged up to 50 kV by the power supply, and the electric charges in the condenser are discharged to the tube after triggering the cathode electrode. The flash x-rays are then produced. The x-ray tube is of a demountable triode that is connected to the turbo molecular pump with a pressure of approximately 1 mPa. As the electron flows from the cathode electrode are roughly converged to the target plane by the electric field in the tube, the weakly ionized plasma x-ray source, which consists of copper ions and electrons, forms by the target evaporating. Both the tube voltage and current displayed damped oscillations, and their peak values increased according to increases in the charging voltage. In the present work, the peak tube voltage was almost equal to the initial charging voltage of the main condenser, and the peak current was about 20 kA with a charging voltage of 50 kV. The dimension of x-ray source was almost equal to the target diameter of about 10 mm, and the x-ray pulse widths were less than 1 μs. When the charging voltage was increased, the plasma x-ray source formed, and the characteristic x-ray intensities of K-series lines substantially increased. The quasi-monochromatic x-rays from the plane-focus tube were formed into parallel beam by a polycapillary plate with a hole diameter and a thickness of 25 μm and 1.0 mm, respectively, and quasi-monochromatic radiography was performed by a film-less computed radiography system.
In the plasma flash x-ray generator, high-voltage main condenser of about 200 nF is charged up to 50 kV by a power supply, and electric charges in the condenser are discharged to an x-ray tube after triggering the cathode electrode. The flash x-rays are then produced. The x-ray tube is of a demountable triode that is connected to a turbo molecular pump with a pressure of approximately 1 mPa. As electron flows from the cathode electrode are roughly converged to a rod iron target of 3.0 mm in diameter by electric field in the x-ray tube, the weakly ionized linear plasma, which consists of iron ions and electrons, forms by target evaporating. At a charging voltage of 50 kV, the maximum tube voltage was almost equal to the charging voltage of the main condenser, and the peak current was about 20 kA. When the charging voltage was increased, the linear plasma formed, and the K-series characteristic x-ray intensities increased. The x-ray pulse widths were about 800 ns, and the time-integrated x-ray intensity had a value of about 10 μC/kg at 1.0 m from x-ray source with a charging voltage of 50 kV. The plasma x-rays were diffused after passing through two lead slits.
A transformer is described, which is build of cables or lines. It can handle ns pulses and can transform voltages or currents in multiples of one. Furthermore it is possible to construct pulse shapes.
Light emitting diodes are very efficient sources of visible and infared light. They have small size and can be combined with fiber optical cables easily. Simple videography can use the wavelength range 400 nm - 1000 nm, which is covered totally by the LED. The speed of modern LED allows flashes shorter than 100 ns in the whole spectral range.
The speed to read out the data of a CCD camera limits applications for high speed videography. If the size of a picture is reduced and if parts of the sensitive area of a CCD are used to store the pictures before reading out, an picture sequence can be stored on a CCD and is available as a standard tv-signal. Cavitation bubbles in an ultrasonic wave have been investigated with a 100 kHz frame rate. Faster frame rates are possible, when a computer is used to separate the lines of agglomerated pictures which are produced by an array of cylinder lenses. An illuminated line is shifted electronically to the neighbored dark field and the next lines can be illuminated. Five pictures in 1 microsecond are realized. An ultrasonic plane wave in a transparent material is an array of cylinder lenses which moves with some mm/microsecond. Four to five pictures with good quality can be taken in a period of the sound wave. A sequence of 200 ns in total is demonstrated with a CCl4 shutter. With a laser modulator crystal a shutter time of 8 ns for each picture was realized. Ideas for faster shutters are presented.
When W. Schaaffs developed X-ray flash machines after World War II at Siemens in Germany, he used spark discharges in layers of liquid between solid plates as a nonmilitary test object. W. Schaaffs discovered the so-called compression ring in 1947 during his experiments with spark discharges. This paper discusses the construction of triode X-ray flash tubes, the evolution of the discharge into the vacuum of the tube and the tubes characteristics depending on this mechanism. It will be found, that the special geometry of the tube shows an important influence on the discharge. The electrons will need a long time to reach the anode while positive ions are strongly accelerated near the anode. The duration of the x-ray flash is limited by the size and speed of the evaporated material from the anode. In the second part of this paper the spark discharge in a layer of liquid between solid plates is described. With this spark discharge it is possible to produce a shock wave in the liquid which finally moves to a vortex. Faster waves propagate in the plates at both sides of the layer. The plate waves induce a low pressure region in front of the ring and there it is possible to detect cavitation bubbles. The spatial arrangement of these bubbles in the layer of liquid between the solid plates depends on the excitation strength of the pulse waves in the plates. Their amplitude depends on the distance to the spark. Thus in a single X-ray flash picture it is possible to study the distribution of the cavitation bubbles for different excitation power. The spatial arrangement of the bubbles can show a periodic structure or it might be chaotic. X-ray flash experiments of this phenomenon will be presented. A model for the birth of cavitation bubbles will be shown. It explains how seeds of phase changes can be distributed in space under special conditions. This idea might also be valid for controlling the crystal growth.
A model for the high voltage breakdown of semiconductors is
developed which can be applied to new high power switches, which were
presented on the 18th ICHSPP, or to well known Zener diodes. Computer
calculations show that a breakdown may result in localiced current
streams. The distribution of the current is inhomogenious in general.
The current distribution may show periodicity in space and in time,
similar to sawtOoth oscillations with a constant frequency. This
frequency can be varied by external parameters. Or it may be chaotic,
then a broad frequency spectrum is produced.
A High-Speed CCD-TV-camera is demonstrated with a frame rate up to
30 kHz. The horizontal resolution is 600 pixels. The vertical
resolution depens on the number of pictures in a high-speed sequence.
It varies from 288 lines for two pictures up to 20 for 28 pictures in
a sequence.
Photocurrents in the ampere range were generated and optically quenched, respectively, in a new type of semiconductor switch on a nanosecond timescale using two lasers of different wavelength. The semi-insulating switch material is GaAs, doped with silicon and compensated with copper, which forms sets of deep acceptors below the middle of the band gap. The photoconductivity in this system is generated by electron and hole ionization from these centers and subsequent fast hole retrapping. Quenching of the photoconductivity is accomplished by hole ionization from copper centers and subsequent electron-hole recombination. The densities of Cu/Si related defects in the various deep levels determine the switch efficiency and its temporal response to the laser pulses. This distribution is very sensitive to variations in the processing procedure of the switch material. Besides photocurrent measurements, Photo-induced Current Transient Spectroscopic (PICTS) studies have been performed in order to determine the activation energy of the deep centers. Additional informations on the deep-level structure of GaAs:Si:Cu were obtained by cathodoluminescence spectra and decay experiments at cryo-temperatures.
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