Alberto Cosentino, Alessia Mondello, Adalberto Sapia, Alessandro D'Ottavi, Mauro Brotini, Enzo Nava, Emanuele Stucchi, Franco Trespidi, Cristina Mariottini, Paul Wazen, Nicolas Falletto, Michel Fruit
This paper describes the laser transmitter assembly used in the ALADIN instrument currently in C/D development phase for the ESA ADM-AEOLUS mission (EADS Astrium as prime contractor for the satellite and the instrument).
The Laser Transmitter Assembly (TXA), based on a diode pumped tripled Nd:YAG laser, is used to generate tunable laser pulses of 150 mJ at a nominal wavelength of 355 nm. This laser is operated in burst mode, with a pulse repetition cycle of 100 Hz.
The TXA is composed of the following units: a diodepumped CW Nd:YAG Laser named Reference Laser Head (RLH), used to inject a diode-pumped, Q-switched, amplified and frequency tripled Nd:YAG Laser working in the third harmonic referred as Power Laser Head (PLH) and a Transmitter Laser Electronics (TLE) containing all the control and power electronics needed for PLH and RLH operation.
The TXA is made by an European consortium under the leadership of Galileo Avionica (It), and including CESI (It), Quantel (Fr), TESAT (Ge) and Thales (Fr).
Atmospheric particle pollution and particles emitted by industrial plants are extremely dangerous for human health. Indeed, they have diameters in such a range (approximately 0.1 - 5 micrometer) that they can penetrate our respiratory system, but cannot be expelled during exhalation. Therefore, it is extremely important to detect them and characterize their size distribution. In this paper we propose the use of a novel instrument recently developed by the authors for the monitoring of airborne particulate at concentration levels so to comply with the current European Economic Community (EEC) regulations. The instrument is based on spectral extinction measurements over long optical paths and is able to recover, almost in real time, both concentration and size distribution of particles with diameters in the range of interest. The sensitivity and accuracy of the instrument were estimated by means of measurements in a clean room and by using calibrated particles dispersed in water. Our results show that, by carrying out measurements over optical paths of approximately$DAL100m, the instrument is able to detect concentration levels well below the ECC limit imposed for the atmospheric pollution. Scaled over shorter optical paths (approximately 10 m), the limit imposed for particle emissions by industrial plants can also be detected very accurately.
We present a low angle light scattering optical particle sizer (measuring range 1-100 micrometers ) utilizing an innovative scheme that enables the instrument to operate at extinction values as small as 10-5. At variance with existing systems, the illuminating beam is properly modulated so to allow a coherent detection scheme to be used. In this way optical and electronic noise can be detected and subtracted from the measured signals therefore increasing the S/N ratio.
The Point Diffraction Interferometer (PDI) is a self-referencing interferometer. A reconfigurable PDI based optical system provided with the automatic control of the alignment has been developed to study fluids in microgravity. It will be flown on board of the IML2 Space Shuttle mission as a part of the Bubble Drop and Particle Unit (BDPU). Main features of the developed system are the automatic control of the alignment and the possibility of changing configuration (from a PDI scheme into a Dark Field mode of operation). To minimize the payload specialist manipulations the system is completely automatic, i.e. the alignment of the system during the start-up operations and the change of configuration are made automatically. System performances have been evaluated during laboratory tests on the apparatus and will be presented here. Future improvements of the PDI apparatus have also been investigated. They mainly concern the laser source, the alignment search procedure and the mechanism of the positioning of the diagnostic tools on the test beam.
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