Semiconductor–Gas-Discharge Device for Fast Imaging in the Infrared
Physics, Engineering and Applications
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The development of high-speed camera systems in the IR range has become topical in last decades in various fields. Among these we mention the ever expanding use of IR lasers in numerous technological applications. For the development of such lasers, beam monitoring is an important issue, including the detailed investigation of the spatio-temporal dynamics of the beam. Other important application fields are material science and high-speed thermal imaging.
Several approaches have been undertaken in order to develop image recording systems in the IR spectral range. One of them consists of using thermal registration media, i.e., media which change their physical properties when being heated by incident radiation. However, despite of considerable efforts the development of high-speed IR recording system on the basis of this technology turned out to fail. The main reason is the low sensitivity and a relatively low dynamic range of such methods.
An alternative approach to create IR imaging devices is to utilize quantumelectronic effects. For this purpose, the external and internal photoeffects are most widely used. The former is applied in optoelectronic devices that are based on a vacuum tube and a photocathode. However, since the IR cut-off of the external
photoeffect does not exceed λ ∼ 1.5 µm, such devices do not allow for a substantial extension of the spectral range into the IR.
Essential progress in developing IR image sensors has been achieved by using solid-state focal plane arrays (FPA). Here, both thermal and quantum detectors can be used as sensitive elements. A drawback of such FPA devices is the long readout time of the image signal of all individual cells. This is a major problem, in particular in the case of big arrays, which are required to provide high spatial resolution.
Since the 70th of the last century, quite a different approach has been pursued in order to develop a high-speed camera system operating in the IR range. Actually, the corresponding system consists of a semiconductor–gas-discharge (SGD) IR image converter, which transfers the incoming IR radiation into the visible, and a high-speed camera capturing visible images at the IR converter output.
The SGD converter operates as follows. The incoming IR radiation field increases conductivity of a high-ohmic photosensitive layer due to the internal photoeffect. The lateral variation of the IR radiation field modulates the resistivity of the high-ohmic layer accordingly. In turn, the latter is in contact with a thin gas layer that is operated as a laterally extended gas-discharge system with the high-ohmic layer as one of the electrodes and a transparent conductive layer as the counter electrode. At a proper choice of parameters, the lateral modulation of the resistivity of the high-ohmic layer is transferred to a laterally modulated emission of luminescence radiation from the gas-discharge layer. As a result, the incoming 2-dimensionl lateral distribution of IR radiation is transferred to a laterally extended radiation field in the visible so that the latter can be captured by existing fast cameras that operate in the visible.
With respect to the operation of the device, the crucial points are: the conversion process takes place in parallel for all effective pixels of a given sensor (matrix) and the conversion process is rather fast, with time constants that may be below 1 µs. In addition, it is indeed possible to find appropriate photosensitive semiconductor materials.
The present book is devoted to reviewing results of the research and development of the SGD device that could be combined with fast modern cameras operating in the visible, with the overall camera system having reasonable spatial resolution, sensitivity and other favourable specifications. By using suitable photosensitive semiconductor materials it has become possible to operate the devices in the IR range up to wavelength of 11 µm with a frame rate that may be beyond 1 Mfps.
In order to realize practical devices, besides the choice of proper photodetector materials, numerous other problems had to be resolved. Here we only mention three of them. In fact, almost all SGD devices with outstanding properties operate at low temperature. Therefore, the problem of handling high voltage supply for the gas-discharge system at low temperature and low gas pressure conditions had to be treated with special attention. Also one was faced with the enormous complexity of the phenomenon of gas discharge. In particular, it turned out that little is known about gas discharge below room temperature. Finally, we mention that the SGD converter is a nonlinear nonequilibrium system that may exhibit diverse instabilities which prevent the system from proper operation. Certainly such instabilities had to be avoided.
The goal of the present book is to review the history of development the SGD devices and report on the efforts that have been undertaken recently to match the device to modern technology and to develop versions that can be the starting point for a commercial product. Essentially, these efforts have been undertaken at the Institut für Angewandte Physik of the Westfälische Wilhelm-Universität, Münster, Germany and the Ioffe Institute, St. Peterburg, Russia.
Several approaches have been undertaken in order to develop image recording systems in the IR spectral range. One of them consists of using thermal registration media, i.e., media which change their physical properties when being heated by incident radiation. However, despite of considerable efforts the development of high-speed IR recording system on the basis of this technology turned out to fail. The main reason is the low sensitivity and a relatively low dynamic range of such methods.
An alternative approach to create IR imaging devices is to utilize quantumelectronic effects. For this purpose, the external and internal photoeffects are most widely used. The former is applied in optoelectronic devices that are based on a vacuum tube and a photocathode. However, since the IR cut-off of the external
photoeffect does not exceed λ ∼ 1.5 µm, such devices do not allow for a substantial extension of the spectral range into the IR.
Essential progress in developing IR image sensors has been achieved by using solid-state focal plane arrays (FPA). Here, both thermal and quantum detectors can be used as sensitive elements. A drawback of such FPA devices is the long readout time of the image signal of all individual cells. This is a major problem, in particular in the case of big arrays, which are required to provide high spatial resolution.
Since the 70th of the last century, quite a different approach has been pursued in order to develop a high-speed camera system operating in the IR range. Actually, the corresponding system consists of a semiconductor–gas-discharge (SGD) IR image converter, which transfers the incoming IR radiation into the visible, and a high-speed camera capturing visible images at the IR converter output.
The SGD converter operates as follows. The incoming IR radiation field increases conductivity of a high-ohmic photosensitive layer due to the internal photoeffect. The lateral variation of the IR radiation field modulates the resistivity of the high-ohmic layer accordingly. In turn, the latter is in contact with a thin gas layer that is operated as a laterally extended gas-discharge system with the high-ohmic layer as one of the electrodes and a transparent conductive layer as the counter electrode. At a proper choice of parameters, the lateral modulation of the resistivity of the high-ohmic layer is transferred to a laterally modulated emission of luminescence radiation from the gas-discharge layer. As a result, the incoming 2-dimensionl lateral distribution of IR radiation is transferred to a laterally extended radiation field in the visible so that the latter can be captured by existing fast cameras that operate in the visible.
With respect to the operation of the device, the crucial points are: the conversion process takes place in parallel for all effective pixels of a given sensor (matrix) and the conversion process is rather fast, with time constants that may be below 1 µs. In addition, it is indeed possible to find appropriate photosensitive semiconductor materials.
The present book is devoted to reviewing results of the research and development of the SGD device that could be combined with fast modern cameras operating in the visible, with the overall camera system having reasonable spatial resolution, sensitivity and other favourable specifications. By using suitable photosensitive semiconductor materials it has become possible to operate the devices in the IR range up to wavelength of 11 µm with a frame rate that may be beyond 1 Mfps.
In order to realize practical devices, besides the choice of proper photodetector materials, numerous other problems had to be resolved. Here we only mention three of them. In fact, almost all SGD devices with outstanding properties operate at low temperature. Therefore, the problem of handling high voltage supply for the gas-discharge system at low temperature and low gas pressure conditions had to be treated with special attention. Also one was faced with the enormous complexity of the phenomenon of gas discharge. In particular, it turned out that little is known about gas discharge below room temperature. Finally, we mention that the SGD converter is a nonlinear nonequilibrium system that may exhibit diverse instabilities which prevent the system from proper operation. Certainly such instabilities had to be avoided.
The goal of the present book is to review the history of development the SGD devices and report on the efforts that have been undertaken recently to match the device to modern technology and to develop versions that can be the starting point for a commercial product. Essentially, these efforts have been undertaken at the Institut für Angewandte Physik of the Westfälische Wilhelm-Universität, Münster, Germany and the Ioffe Institute, St. Peterburg, Russia.
| Erscheinungsdatum | 20.05.2016 |
|---|---|
| Reihe/Serie | Berichte aus der Physik |
| Verlagsort | Aachen |
| Sprache | englisch |
| Maße | 170 x 240 mm |
| Gewicht | 317 g |
| Einbandart | geklebt |
| Themenwelt | Naturwissenschaften ► Physik / Astronomie ► Angewandte Physik |
| Schlagworte | Gas Discharge • high resistivity electrode • high-speed IR imaging • IR image converters • IR range • semiconductor gas discharge converter • semiconductor gas discharge system • short-gap discharges |
| ISBN-13 | 9783844006674 / 9783844006674 |
| Zustand | Neuware |
| Informationen gemäß Produktsicherheitsverordnung (GPSR) | |
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