The optical scheme of a multispectral thermal imager (MSTI) is reviewed on the basis of a staring
thermal imager and interferometers set at the Brewster angle to the optical axis of the device. The
calculations of a usable sensitivity, resolving power and other parameters of this device are carried
out.
The filtering device on the basis multiplex the Fabry-Perot interferometers and imaging spectrometer keeping this
device and a matric thermal imager is offered. The calculations of parameters of this filtering device and imaging
spectrometer are conducted. It is expected that the similar devices can be suitable for imagery of objects in given
narrow spectral ranges.
The optical scheme of a multispectral thermal imaging (MSTI) is reviewed on the basis of a staring thermal imaging and
interferometers established bevel way of a Brewster to an axis of sighting of the device. The calculations of a usable
sensitivity, resolving power and other parameters of this device are conducted.
Parameter calculations were carried of filtering devices in one of which the phenomenon of the total internal reflection
was used. It is expected that these devices may be suitable for imagery of objects in the given narrow spectral bands -
spectral imaging (SI) and for obtaining the spectral maps of fast flowing past processes.
In the report the works devoted to methods and technique of a spectral thermal imaging are considered. For deriving the
spectral images of objects are used as methods of an immediate optical filtration with the help of tunable spectral filters
of different types (optical-acoustic, interference, interferential - polarization, filters on the basis of total interior reflection
and other), and methods of selection of the spectral images grounded on mathematical handling of optical fields,
recorded by a matrix photodetector (for example, after a Fourier-interferometer, holograms and other). The principles of
spectral selection of the images and paths of build-up spectral thermal imagers are analyzed.
Parameter calculations were carried out for two types of filtering devices in one of which the phenomenon of the total internal reflection was used and in the other the multibeam interference was used for the optical radiation filtering. It is expected that these devices may be suitable for imagery of objects in the given narrow spectral bands - spectral imaging (SI).
LWIR staring 384x288 focal plane array (FPA) has been developed and investigated. FPAs are manufactured on the basis of mercury cadmium telluride epitaxial layers grown both by liquid phase epitaxy (LPE) and molecular beam epitaxy (MBE).
384x288 FPA consists of a MCT photodiodes array formed in the p-type layer by ion implantation and silicon readout integrated circuit (ROIC). The photodiodes array pitch in each direction is 28 μm. ROIC performs the photocurrents integration during row period, signals multiplexing in two output channels from the focal plane. MCT photovoltaic array and ROIC are bonded by indium bumps. This photosensitive assembly is packaged in vacuum metal encapsulation and cooled down to temperature 80 K. Average detectivity was of 4.4.1010 W-1.cm.Hz1/2 for FPA cutoff wavelength of 10.7 μm. Test IR system on the basis of FPA was developed to obtain thermal images in real time mode at frame frequency 50 Hz. Test IR system performs two-point correction and defective elements replacement.
Possibility of the use of thermal radiation ofthe mouth cavity ofthe operator for calibration of infrared pyrometers in field conditions is discussed. On the basis ofexperimental results errors of such method ofcalibration are evaluated.
Methods of measuring relative spectral responsivity of an exemplary photodetector in 2-14 μm spectral range with the help of an absolutely black body and spectral filters are discussed.
KEYWORDS: Sensors, Temperature metrology, Black bodies, Modulation, Signal detection, Calibration, Error analysis, Power supplies, Switches, Distance measurement
A comparative analysis of methods of determination of irradiance values in the plane of location of sensitive elements (SE) of detectors in measuring installations containing an absolutely black body (ABB) was carried out.
A FPA architecture and technology developed by RD&P Center ORION based on planar HgCdTe photodiode arrays and cooled silicon integrated readout circuits is presented. Photovoltaic detectors array made on mercury cadmium telluride (MCT) liquid phase epitaxy (LPE) layer and silicon readout circuits are linked by indium bumps on sapphire interconnection substrate. Cooled silicon readout circuits have been made by n-MOS technology with no TDI stages at focal plane. For 8-12 μm wavelength range detectivity is (5-10)×1010 cmW-1Hz1/2 for 2x256 FPA with two TDI elements.
LWIR staring at 384x288 focal plane array (FPA) have been developed and investigated. FPAs are manufactured on the base of mercury cadmium telluride epitaxial layers grown both by liquid phase epitaxy (LPE) and molecular beam epitaxy (MBE). 384x288 FPA consists of a MCT photodiodes array formed in the p-type layer by ion implantation and silicon MOS-multiplexer. The photodiodes array pitch in each direction is 35 micrometers . Multiplexer performs the photocurrents integration during line period, signals multiplexing and output form the focal plane. MCT photovoltaic array and MOS-multiplexer are bonded together by indium bumps. Sensitive unit is packaged in a metal dewar and cooled down to temperature 80 K. Average detectivity was more than 1.5x1010W-1cm/s-1/2 for FPA with cutoff wavelength of 11.9 micrometers at T=80K. Test IR system on the base of FPA was developed to obtain IR-images in real time mode with frame frequency 25 Hz. Test IR system performs two-point image correction and defective elements replacement.
The calculations of noise equivalent temperature difference (NETD) for thermovision devices are carried out, with cut- off wavelengths of photo detectors ((lambda) co) and distance to target used as parameters. For the estimation of influence of the photodiode spectral characteristics on the parameters of thermovision systems several characteristics were taken into account: the spectrum of radiation of object, transmission of an atmosphere and spectral characteristic of sensitivity of photo-diode array. The results show that an increase of (lambda) co above 10.5 microns at small distances improves the temperature resolution in degradation of temperature resolution (increase NETD).
Current-voltage characteristics of LN2 cooled MCT p-n tunnel junctions have been investigated. The negative differential conductance takes place at negative total current due to photocurrent bias. This gives possibility of current oscillation without external electric power.
IR imager have been developed and investigated. IR imager consists of mercury cadmium telluride 128 X 128 staring focal plane array bonded by indium bumps with silicon MOS- multiplexer, split-Stirling cooler, electronic signal processor. Noise equivalent temperature difference NETD is less than 0.1 K.
LWIR staring 128 X 128 and 384 X 384 focal plane arrays (FPA) have been developed and investigated. FPAs have been manufactured on the base of mercury cadmium telluride epitaxial layers grown both by liquid phase epitaxy and molecular beam epitaxy. The photodiode array was bonded via the indium bumps to the silicon MOS-multiplexer, which ensure reading, integration and output of the photosignals from the focal plane. Performances of FPAs produced by these different epitaxial methods are analyzed.
Using Fourier Transform Spectroscopy (FTS), we have measured HgCdTe diodes and resistors photoresponse at wavelengths below the fundamental absorption edge in this semiconductor. This study is inherent to FTS photoresponse and is performed by the long wavelength radiation modulation of the short wavelength photocurrent. Possible physical mechanisms of such modulation are discussed.
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