Hazardous chemicals detection systems based on cascade lasers are wider and wider used for monitoring the earth
atmosphere pollution, as well as in the safety apparatus installed in buildings of public services. The main feature of
these systems is a high sensitivity that for the most advanced set ups allows detecting chemical substances at the level of
single ppt (part per trillion).
In this paper, we present a measuring system dedicated to detecting hazardous chemical substances in which
a semiconductor cascade laser has been implemented for the generation of IR radiation. The system operation and
potentialities are exemplified by its application to detecting and monitoring the ammonia concentration in the air.
In the paper the authors present a laser warning receiver in air version for helicopter. Its parameters, block diagram and
operation mode are described.
The paper presents method of acquiring a new form of statistical information about the changes at scenery, overseen by thermal imaging camera in static configuration. This type of imagers reach uniquely high efficiency during nighttime surveillance and targeting. The technical issue we have solved, resulted from the problem: how to verify the hypothesis that small, nocturnal rodents, like bank voles, use common paths inside their range and that they form a common, rather stable system? Such research has been especially difficult because the mentioned mammals are secretive, move with various speed and due to low contrast to their natural surroundings - as leaves or grass - nearly impossible for other kind of observations from a few meters distance. The main advantage of the elaborated method showed to be both adequately filtered long thermal movies for manual analyses, as well as auto-creation of the synthetic images which present maps of invisible paths and activity of their usage. Additional file with logs describing objects and their dislocations as the ".txt" files allows various, more detailed studies of animal behavior. The obtained results proved that this original method delivers a new, non-invasive, powerful and dynamic concept of solving various ecological problems. Creation of networks consisted of uncooled thermal imagers - of significantly increased availability - with data transmissions to digital centers allows to investigate of moving - particularly heat generated - objects in complete darkness, much wider and much more efficiently than up today. Thus, although our system was elaborated for ecological studies, a similar one can be considered as a tool for chosen tasks in the optical security areas.
The performance of uncooled photodetectors operating in the middle and long wavelength spectral range is limited by the noise originated from thermal generation and recombination processes in semiconductors. The noise level exponentially increases with decreasing band gap of the semiconductor. Therefore, the uncooled short wavelength devices are characterized by good performance while the long wavelength ones are much less sensitive. The consequence is very poor performance of long wavelength devices at short wavelength range. We report here two-lead multilayer photoconductors that operate over a wide spectral band with performance improved by a large factor at short wavelength ranges. The devices consist of several stacked active regions (absorbers) with their outputs connected in parallel so the resulting output signal current is the sum of the signals generated at all active regions. Due to a high photoelectric gain in the wider gap absorbers and low thermal generation and recombination, the devices offer significantly better performance at short wavelengths while the long wavelength response remains essentially unaffected. The practical devices have been obtained using complex Hg1-xCdxTe heterostructures grown on CdTe or GaAs substrates by ISOVPE, MOCVD or combination of the two epitaxial techniques. An example is an uncooled photoconductor operating up to 11μm, with response at 0.9-4μm increased by ≈3 orders of magnitude in comparison to the conventional 11 μm device.
This paper presents preliminary results of the project brought up with aim to verify the hypothesis that small, nocturnal rodents use common paths which form a common, rather stable system for fast movement. This report concentrates on results of merging uniquely good detecting features of modern IR thermal cameras with newly elaborated software. Among the final results offered by this method there are both thermal movies and single synthetic graphic images of
paths traced during a few minutes or hours of investigations, as well as detailed numerical data of the ".txt" type about chosen detected events. Although it is to early to say that elaborated method will allow us to answer all ecological questions, it is possible to say that we worked out a new, valuable tool for the next steps of our project. We expect that this method enables us to solve the important ecological problems of nocturnal animals study. Supervised, stably
settled area can be enlarged by use of a few thermal imagers or IR thermographic cameras, simultaneously. Presented method can be applied in other uses, even distant from presented e.g. ecological corridors detection.
The short history of the laser warning receivers (LWR) development was presented by the tank systems. The theoretical analysis concerns the device which applies the special uncooled multispectral detectors. The theoretical results are confirmed by measurements in real conditions.
Predicted ways of development of the LWR devices and the proceeding changes extending their possibilities were shown.
Computer simulation of multispectral detection of laser radiation is presented. The theoretical analysis concerns the device which applies the special uncooled MPC detectors. The theoretical results are confirmed by measurements in real conditions.
Computer simulation of uncooled Hg1-1CdxTe detectors is presented. Based on the obtained characteristics the possibility of detector application in laser radiation multispectral detection of laser radiation is estimated.
Theoretical design and practical performance of uncooled MPC detectors are presented. Based on the detectors performances the possibility of detector's application in laser radiation multispectral detection is showed.
There are many infrared systems which require detectors with controlled spectral responsivities. One of the examples is laser warning device. The spectral response of detectors for this particular application should cover a wide spectral range from about 0.6 micrometer to 11 micrometer. Thermal detectors are unselective, but they suffer from poor speed of response. In contrast, the photon detectors exhibit much better speed of response and sensitivity. The spectral responsivities of conventional photodetectors are close to that of the ideal photon counter with a given cut-off wavelength. It means that responsivities at short wavelength are highly reduced. Here we report MPC IR photodetector, which covers the required spectral band of 0.6 - 11 micrometers, exhibiting increased at short wavelengths. Calculation results of range of device which applies these detectors also are presented.
A brief description of construction, as well as investigation of properties of the multispectral non-cooled infrared detector, is being presented below. The detector's construction enables its sensitivity control in a wide spectrum range from 0.6 up to 11 micrometers .
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