Infrared detector array sensors for remote gas detection

This paper investigates the potential of infrared detector arrays for passive gas detection systems. At present, extractive methods are commonly used for the detection of gases and vapours. In case of large distances or in the open atmosphere remote measurement systems have to be employed. Remote detection can be used to monitor industrial and traffic emissions and to detect defects and leaks. Usually, the basic measurement principle is active and double ended: e.g. the sampling distance is probed by rays of light and the spectral transmission is measured. For example, using tunable laser sources in the mid-infrared roadside monitoring of the emissions of single moving cars can be achieved . However, establishing and alignment of the necessary closed optical path for such measurements (light source, retroreflector) is always time consuming, and may be rather difficult since it needs access to both ends of the path. LIDARs are single ended systems, but those systems are in most cases im practical due to size, weight, and cost. In such cases a single ended and in particular a passive sensor approach is more suitable than an active technique. A passive sensor approach has to prove sufficient sensitivity and selectivity but it is the only viable approach under weight and cost restrictions in particular for mobile applications. Infrared spectroscopy is an established technique to detect most molecular gases. The 8-12 mu m atmospheric window is part of the infrared fingerprint region where many organic substances can be identified. Using the ubiquitous thermal radiation as background results in a high versatility of passive sensing systems. Usually mid infrared spectroscopy is the domain of Fourier-transform-infrared (FTIR)-spectrometers. They have been successfully used for remote sensing of smoke stack and flare emissions. However, in case of remote gas detection they suffer from typical shortcomings like errors caused by fluctuations of the signal during scanning and ne ed of a high dynamic range. The infrared detector array sensor (IDAS) is an advantageous alternative for the spectrometer. IDAS systems are more robust than FTIR-spectrometers and do not suffer from the sensitivity restrictions of conventional (single detector) grating spectrographs. In addition, IDAS spectroscopy benefits from the rapid technological progress of detector arrays which are usually employed in thermal imaging systems

Processing of Polyamide Electrospun Nanofibers with Picosecond Uv-laser Irradiation

AbstractTo optimize the cell colonization on electrospun polyamide nanofibers, the fiber scaffolds were processed with picosecond uv-laser irradiation. The ablation thresholds were determined in dry, wet and immersed condition. The morphology of the ablated areas was evaluated by confocal and scanning electron microscopy. It was found that the ablation thresholds of the nanofiber tissues are lower as for polyamide bulk material. While on bulk samples the ablation spot sizes are close to the focal diameter, on the fiber samples the ablation spots are more extended. Light scattering in the fiber tissue has to be taken into account. The results show that with exact setting of the laser parameters it is possible to reduce the heat-affected zone to a few micrometer. In addition, changing of the nanofiber tissue wettability by laser radiation was investigated

Laser processing of dry, wet and immersed polyamide nanofiber nonwovens with different laser sources

Electrospun nanofiber scaffolds of different polymers are used in tissue engineering to mimic the extracellular matrices with favourable conditions for cell growth and proliferation. Structures such as cavities, holes and cuts in the scaffolds can be used to optimize cell growth. We investigated the influence of different laser sources used for direct laser writing on the cutting and structuring quality of electrospun polyamide nonwovens. Ablation thresholds and rates were determined. Because of different approaches in cell colonization with scaffolds, the investigations were carried out on dry, wet and immersed nonwovens. The results show that femto- and picosecond lasers are very well suited for processing of dry nonwovens. Processing with green wavelengths is more effective and leads to similar minimum feature sizes than in the ultraviolet range. Ablation rates up to 8000 µm³/pulse were obtained which are about a factor of 100 higher than those for polyamide bulk material. Nanosecond UV lasers produced structures of reduced quality. Excimer lasers at 193 nm offer a possible alternative for large-area structures when operated at low fluences. Processing of wet and immersed nanofibers is possible with smaller processing speed and with a slightly degraded quality