Yuri A. Astrov

Plasma spots in a gas discharge system: birth, scattering and formation of molecules

Abstract Experiments on a planar gas discharge device, where formation of spatial structures is of the Turing origin, demonstrate that particle-like states of a pattern can scatter at each other, form bound (“molecular”) states that propagate over the active area of the device, and generate additional quasi-particles in the course of collisions.

Noise properties of a high-speed semiconductor-gas-discharge infrared imager

The imager consists of a planar semiconductor-gas discharge (SGD) cell allowing the ultra fast IR-to-visible conversion with response time on the microsecond scale. The semiconductor wafer is made of Si:Zn providing the spectral range of 1.1 - 3.5 micrometers . The 100 micrometers discharge gap is filled with Ar under the pressure of 100 hPa. The cell is cooled down approximately to 90 K. Among studied properties are noise, both in time and space domains, detectivity, noise equivalent irradiance and, when applying the imager in a thermal imaging system, noise equivalent temperature difference (NETD). Investigations of the spatial noise and NETD have been carried out by using a low-noise CCD camera capturing output images of the SGD cell. For measuring the temporal noise, a low-noise photomultiplier is used to detect gas discharge radiation from the area of about one resolved pixel. The own noise of the SGD cell is found by comparing signal-noise dependencies obtained at acquiring outgoing light of the cell, on the one hand, with those at observing a thermal radiation source with well describable photon noise, on the other hand. The results indicate that the imager has surprisingly low noise which is very close to the photon-noise limit.

Application of high-speed IR converter in scientific and technological research

The infrared (IR) image converter is based on a planar semiconductor-gas discharge structure operating at a temperature of about 100 K in the spectral range of 1.1 to 3.5 micrometers . Semiconductor material and gas are Si:Zn and Ar respectively. The conversion of input IR images into the visible is characterized by a time constant in the order of a few microseconds, the dynamic range is at least 104 and good linearity is observed. Together with the Hamamatsu framing camera C4187 the IR converter has been applied to investigate in the microsecond range the spatio-temporal dynamics of radiation of 1.318 micrometers Nd:YAG laser. The second application was the study of the mode evolution of an Er:YSGG laser operating at a wavelength of 2.79 micrometers and an Er:YAG laser with a wavelength of 2.94 micrometers using a pulse length of 100 to 150 microsecond(s) , and a pulse energy of about 40 mJ. In this case, the IR converter is combined with an intensified CCD camera, of which the exposure time is down to 10 microsecond(s) . In the third application, the IR converter is used in combination with a fast CMOS camera to monitor Nd:YAG laser welding of stainless steel samples at the rate of 320 frames/s.

Spatially and temporally resolved IR image detection with a semiconductor-gas-discharge device

We suggest a method for spatially and temporally resolved IR-image detection by using a semiconductor-gas discharge (SGD-) structure. The operation of the device is based on the conversion of IR-radiation into the visible spectral range. Especially, we discuss the influence of the system parameters on the operation of the device and propose a technical realization for a real time IR-image conversion camera based on the converter cell in connection with a standard CCD-camera. In combination with a gateable CCD-camera or an electron-optical recording technique (e.g., streak- or framing camera), the converter structure could be used for high speed IR-imaging in the microsecond range.

Sensitivity performance of ultrafast IR imaging systems in the basis of a planar semiconductor-gas discharge IR-to-visible converter

Sensitivity of IR imaging systems based on a planar semiconductor-gas discharge (SGD) cell is considered. These systems feature conversion of IR images into visible ones with the response time on the microsecond scale. A converted (visible) image at the cell output is captured by an image sensor coupled to the cell either with a lens or with a fiber optic taper. Comparison of both methods shows that fiber tapers can provide much higher ultimate coupling efficiency but has less flexibility in usage and bring in a high additional heat load on the cooling unit. Obtained equations allow calculation of sensitivity for the whole system, taking into account such parameters of its constituents as the conversion efficiency and dark current density of the IR converter cell, readout noise of the image sensor, light transfer efficiency from the cell to the sensor, as well as the equivalent pixel area in the gas discharge plane and the exposure duration. The equations are applied to evaluate sensitivity of the IR imaging system utilizing a SGD cell filled with argon, where a Si:Zn semiconductor sensitive in a spectral range of 1.1 - 3.5 μm is used. The results demonstrate the possibility of achieving quite a high sensitivity performance of considered systems.

Speed properties of a gas-discharge gap IR-visible converter studied with a streak-camera system

Under certain experimental conditions a semiconductor-discharge gap structure can be used as detector for spatio-temporal resolved measurements on IR radiation. We investigate experimentally the speed properties of this kind of converter by using a streak camera system and a semiconductor laser diode ((lambda) equals 1.3 micrometers ). The experimental results are compared with the predictions of a simple theoretical model.

An IR-Visible Converter for Spatially and Temporally Resolved IR-Image Detection

Electron-optical devices are broadly used nowadays in experimental physics, technology research and technical applications for high-speed recording. Fast processes can be studied with these devices in framing and streak modes1, thus giving vast information on the spatiotemporal evolution of optical fields in a broad spectral range. Especially, in the visible, ultraviolet (X-ray) and near infrared (IR) spectral ranges, these methods are efficient. But unfortunately, many of them lose sensitivity for wavelengths of incoming light larger than λ > 1.3 µm. In this contribution we present a technique that will allow spatio-temporal resolved high-speed recording even at wavelengths beyond 1.3 µm. We will also demonstrate, that this technique can be used for the spatially and temporally resolved measurement of temperature distributions on the surface of heated bodies.