Luminescence of a single upconverting particle (NaYF4:Er3+,Yb3+) can be used to determine the optical trap temperature due to the partial absorption of the trapping beam either by the medium (water) or the optically trapped particle itself. This fact is an important drawback can be reduced by shifting the trapping wavelength out of the water absorption band, or by using time-modulated laser trapping beams. Both approaches have been studied and the results have shown that the thermal loading due to the trapping radiation can be minimized.
Satellite instruments detected two intense decreases of the ozone column values over Europe in November 1996 and November 1999. These low ozone events have been studied using atmospheric data and air parcel trajectory analyses. It was found that both ozone events were accompanied by rapid temperature decreases in the lower stratosphere. The anti-correlation found between total ozone and air parcel height along the air parcels trajectories suggested that the vertical displacement of air contributed significantly to the total ozone and temperature decreases observed. The Azores high-pressure cell over the mid Atlantic region, perturbed the flow in the lower stratosphere, forcing the vertical displacement of air parcels and causing the temperature and total ozone minima observed.
In 1993 a network of differential optical absorption instruments was deployed in Argentina and Chile to study the evolution of the ozone layer in the mid latitudes of South America. The data obtained by this network were compared with the data provided by TOMS (NASA) and TOVS (NOAA) satellite instruments and a good correlation was found. NCAR meteorological data were also used to study in detail the ozone transport in the stratosphere under ozone hole conditions. The data provided by both, the ground based and the spaceborne instruments, revealed that sudden and transient decreases of total ozone column values took place in the mid-latitudes of South America each spring in the period 1993 - 1998. These low ozone events occurred quasi- simultaneously at quite different latitudes. The analysis of potential vorticity maps showed that the lower stratosphere polar vortex penetrated up to approximately latitude 50S in South America every spring since 1993. In addition it was found that the low ozone events were accompanied by sudden air temperature decreases in the lower stratosphere. The computation of the 3D back-trajectories of air parcels showed that air from the surroundings of the ozone hole were transported to the mid latitudes regions. An anti- correlation between air parcels height and total ozone along the trajectory was found suggesting that vertical displacement of air also contributed to the observed ozone and temperature decreases.
In the recent years, the depletion of the stratospheric ozone layer has alerted the scientific community about the risks of a solar ultraviolet (UV) radiation overexposure. Biological research has confirmed the very important role of the UV-B (320 - 280 nm) and UV-A (400 - 320 nm) bands on the Earth biosystem. AlxGa1-xN semiconductor alloys, with a bandgap tunable between 3.4 eV and 6.2 eV, are the most suitable materials for the fabrication of solar UV detectors. In this paper we describe the fabrication and characteristics of AlGaN photoconductive and Schottky barrier photodetectors, with Al mole fractions up to 35%. Photoconductive detectors show very high gains, that decrease with increasing incident optical power. They present persistent photoconductivity effects, and a significant below-the-gap response. The physics of this behavior is discussed. On the other hand, AlGaN Schottky barrier photodetectors show a very fast response that is independent of the optical power, and their UV/visible rejection ratio is rather high. As the Al content increases, the evolution of the responsivity and cut-off wavelength is presented. Al0.22Ga0.78N Schottky barriers are very good candidates to monitor the UV-B band. The prospective applications of AlGaN photodiodes to determine the biological action of the solar UV radiation are also discussed.
In this work, experimental results obtained with the first Spanish LIDAR-DIAL prototype are presented. This DIAL consists of the well-known configuration of a dye laser as the tuning element, pumped by a Nd:YAG laser. In order to evaluate the performance of this DIAL, parallel measurements of SO2 from industrial point sources with a passive remote technique were carried out. The spectrometer used as reference instrument was a COSPEC V, widely used for SO2 concentration measurements from natural and anthropogenic plumes. Due to the different nature of these remote techniques, it has been necessary to design several field experiments and to homogenize all data before comparison. In this sense, the SO2 traceability, because of its high chemical stability in the atmosphere, has been important to assess the performance of the DIAL system by using this experimental strategy. Also, the data obtained from the continuous monitoring of the emissions in the stacks are in good agreement with those provided by the remote sensors. It can be concluded that the new DIAL system works properly in a 4 Km range. Quality control of industrial emission inventories can be considered as a promising line of application of this DIAL system.