The effects of the 20 March 2015 partial solar eclipse on irradiance measurements, Planetary Boundary Layer (PBL) height, meteorological and turbulence parameters, and near surface particle properties have been investigated at Lecce (40.3°N, 18.1°E, 30 m a.s.l.), southeastern Italy. Each solar eclipse represents always a unique event, since it is characterized by a particular time of the day, season, location, and synoptic conditions, and allows investigating the atmospheric processes driven by a fast decrease of the solar radiation. According to the astronomic data, the eclipse started at the study site at about 08:30 UTC and ended at 10:47 UTC, reaching the maximum obscuration of the solar disk (43.6%) at about 09:37 UTC. Short-wave irradiance measurements revealed that the eclipse direct radiative forcing at the surface was equal to -307 W m-2 at the maximum obscuration of the solar disk. A lidar system operating at the study site within the European Aerosol LIdar NETwork (EARLINET) was used to investigate both the atmospheric turbulence weakening driven by the eclipse cooling effect and the PBL height time evolution. It has been found that the PBL height that was equal to 300 ± 30 m before the eclipse onset decreased up to 210 ± 20 m after the eclipse full phase. Measurements from a micrometeorological station have instead been used to investigate the atmospheric turbulence weakening at the ground level by the changes of turbulent kinetic energy. Integrating nephelometer measurements revealed that the solar eclipse was also responsible for the increase of the near surface particle scattering coefficient, mainly because of the increase of the fine-mode particle concentration.
In the framework of the ChArMEx (Chemistry-Aerosol Mediterranean Experiment, http://charmex.lsce.ipsl.fr/) initiative, a field campaign took place in the western Mediterranean Basin between 10 June and 5 July 2013 within the ADRIMED (Aerosol Direct Radiative Impact on the regional climate in the MEDiterranean region) project. The scientific objectives of ADRIMED are the characterization of the typical “Mediterranean aerosol” and its direct radiative forcing (column closure and regional scale). This work is focused on the multi-intrusion Saharan dust transport period of moderate intensity that occurred over the western and central Mediterranean Basin during the period 14 – 27 June. The dust plumes were detected by the EARLINET/ACTRIS (European Aerosol Research Lidar Network / Aerosols, Clouds, and Trace gases Research InfraStructure Network, http://www.actris.net/) lidar stations of Barcelona (16 and 17 June) and Lecce (22 June). First, two well-known and robust radiative transfer models, parametrized by lidar profiles for the aerosol vertical distribution, are validated both in the shortwave and longwave spectral range 1) at the surface with down- and up-ward flux measurements from radiometers and 2) at the top of the atmosphere with upward flux measurements from the CERES (Clouds and the Earth’s Radiant Energy System) radiometers on board the AQUA and TERRA satellites. The differences between models and their limitations are discussed. The instantaneous and clear-sky direct radiative forcing of mineral dust is then estimated using lidar data for parametrizing the particle vertical distribution at Lecce. The difference between the obtained forcings is discussed in regard to the mineralogy and vertical structure of the dust plume.
The development of the Global Position System (GPS) satellite network provides new opportunities to
characterize atmospheric parameters using innovative techniques. The GPS Radio Occultation Technique
(GPS RO) is one of the most recent and promising atmospheric remote sensing technique applied to GPS
measurements. The GPS RO technique allows obtaining profiles of refractivity, temperature, pressure and
water vapor in the neutral atmosphere and electron density in the ionosphere. In the last years, other
missions confirmed the RO efficiency, like GPS/MET, COSMIC (Constellation Observing System for
Meteorology, Ionosphere, and Climate), Formosa Satellite Mission 3 and the last Radio Occultation
Sounder Antenna for the Atmosphere.
In this work, water vapor mixing ratio profiles retrieved from COSMIC observations are presented and
validated using ground based water vapor Raman lidar profiles. As far as we know, this is the first time
water vapor mixing ratio profiles provided by COSMIC are compared with a ground based Raman lidar.
COSMIC profiles used in this study are retrieved applying a one-dimensional variational method that make
use of ECMWF low resolution analysis data as a guess of atmospheric water vapor. Raman lidar
measurements of the water vapor mixing ratio profiles are provided by PEARL (Potenza EArlinet Raman
Lidar) system running at CIAO, located in Potenza, South Italy.
Performance of COSMIC retrieval are studied over a period of one year (2008) of systematic water vapor
Raman lidar measurements. A possible strategy for reducing the impact of the co-location mismatch
between satellite footprint and the lidar station is presented and the problem of the vertical resolution of
COSMIC profiles respect to the Raman lidar is also discussed.
The statistical analysis for the selected cases shows good performance of COSMIC in the identification of
the vertical gradients of the water vapor field, even though the average difference between the Raman lidar
and the COSMIC profiles suggests that caution should be taken in using COSMIC data as an absolute or
reference measurement of water vapor, in particular in the low and middle troposphere.
EARLINET, the European Aerosol Research Lidar NETwork, established in 2000, is the first coordinated lidar network
for tropospheric aerosol study on the continental scale. The network activity is based on scheduled measurements, a rigorous quality assurance program addressing both instruments and evaluation algorithms, and a standardised data
exchange format. At present, the network includes 27 lidar stations distributed over Europe.
EARLINET performed almost continuous measurements since 15 April 2010 in order to follow the evolution of the
volcanic plume generated from the eruption of the Eyjafjallajökull volcano, providing the 4-dimensional distribution of
the volcanic ash plume over Europe. During the 15-30 April period, volcanic particles were detected over Central Europe
over a wide range of altitudes, from 10 km down to the local planetary boundary layer (PBL). Until 19 April, the
volcanic plume transport toward South Europe was nearly completely blocked by the Alps. After 19 April volcanic
particles were transported to the south and the southeast of Europe. Descending aerosol layers were typically observed
all over Europe and intrusion of particles into the PBL was observed at almost each lidar site that was affected by the
volcanic plume. A second event was observed over Portugal and Spain (6 May) and then over Italy on 9 May 2010. The
volcanic plume was then observed again over Southern Germany on 11 May 2010.
Lidar techniques represent the most suitable tool to obtain information on the aerosol vertical distribution and therefore
to close this kind of observational gap. Lidar networks are fundamental to study aerosol on large spatial scale and to
investigate transport and modification phenomena. These are the motivations why EARLINET, the European Aerosol
Research Lidar Network, was established in 2000. At present, EARLINET consists of 25 lidar stations: 7 single
backscatter lidar stations, 9 Raman lidar stations with the UV Raman channel for independent measurements of aerosol
extinction and backscatter, and 9 multiwavelength Raman lidar stations (elastic channel at 1064 nm, 532 nm, 355 nm,
Raman channels at 532 nm and 355 nm, plus depolarization channel at 532 nm) for the retrieval of aerosol microphysical
properties.
EARLINET data can significantly contribute to the quantification of aerosol concentrations, radiative properties, long-range
transport and budget, and prediction of future trends on European and global scale. It can also contribute to
improve model treatment on a wide range of scales and to a better exploitation of present and future satellite data.
EARLINET is playing an important role in the validation and in the full exploitation of the CALIPSO mission.
EARLINET started correlative measurements for CALIPSO since June 2006. A strategy for correlative measurements
has been defined on the base of the analysis of the high resolution ground track data provided by NASA. Results in terms
of comparisons between EARLINET and available CALIPSO products, both level 1 and level 2 data, are presented.
The present knowledge of the aerosol distribution is not sufficient to estimate the aerosol influence on global and
regional environmental conditions and climate. This observational gap can be closed by using advanced laser remote
sensing. EARLINET (European Aerosol Research Lidar Network) is the first aerosol lidar network, established in 2000,
with the main goal to provide a comprehensive, quantitative, and statistically significant database for the aerosol
distribution on a continental scale. EARLINET is a coordinated network of European stations (25 at present) using advanced lidar methods for the vertical profiling of aerosols. The network activity is based on simultaneous scheduled
measurements, a rigorous quality assurance program addressing both instruments and evaluation algorithms, and a
standardised data exchange format. Further observations are performed to monitor special events.
EARLINET-ASOS (Advanced Sustainable Observation System) is a five year EC Project started in 2006, based on the
EARLINET infrastructure. The main objectives are: to make EARLINET a world-leading instrument for the observation
of the 4-D aerosol distribution on continental scale; to foster aerosol-related process studies, validation of satellite
sensors, model development and validation, assimilation of aerosol data into operational models; and to build a
comprehensive climatology of the aerosol distribution.
The European Aerosol Research Lidar Network (EARLINET) was established in 2000 to derive a comprehensive, quantitative, and statistically significant data base for the aerosol distribution on the European scale.
At present, EARLINET consists of 25 stations: 16 Raman lidar stations, including 8 multi-wavelength Raman lidar stations which are used to retrieve aerosol microphysical properties.
EARLINET performs a rigorous quality assurance program for instruments and evaluation algorithms. All stations measure simultaneously on a predefined schedule at three dates per week to obtain unbiased data for climatological studies.
Since June 2006 the first backscatter lidar is operational aboard the CALIPSO satellite. EARLINET represents an excellent tool to validate CALIPSO lidar data on a continental scale. Aerosol extinction and lidar ratio measurements provided by the network will be particularly important for that validation.
The measurement strategy of EARLINET is as follows: Measurements are performed at all stations within 80 km from the overpasses and additionally at the lidar station which is closest to the actually overpassed site. If a multi-wavelength Raman lidar station is overpassed then also the next closest 3+2 station performs a measurement.
Altogether we performed more than 1000 correlative observations for CALIPSO between June 2006 and June 2007.
Direct intercomparisons between CALIPSO profiles and attenuated backscatter profiles obtained by EARLINET lidars look very promising.
Two measurement examples are used to discuss the potential of multi-wavelength Raman lidar observations for the validation and optimization of the CALIOP Scene Classification Algorithm.
Correlative observations with multi-wavelength Raman lidars provide also the data base for a harmonization of the CALIPSO aerosol data and the data collected in future ESA lidar-in-space missions.
EARLINET-ASOS (European Aerosol Research Lidar Network - Advanced Sustainable Observation System) is a 5-year EC Project started in 2006. Based on the EARLINET infrastructure, it will provide appropriate tools to improve the quality and availability of the continuous observations. The EARLINET multi-year continental scale data set is an excellent instrument to assess the impact of aerosols on the European and global environment and to support future satellite missions. The project is addressed in optimizing instruments and algorithms existing within EARLINET-ASOS, exchanging expertise, with the main goal to build a database with high quality aerosol data. In particular, the optimization of the algorithms for the retrieval of the aerosol optical and microphysical properties is a crucial activity. The main objective is to provide all partners with the possibility to use a common processing chain for the evaluation of their data, from raw signals to final products. Raw signals may come from different types of systems, and final products are profiles of optical properties, like backscatter and extinction, and, if the instrument properties permit, of microphysical properties. This will have a strong impact on the scientific community because data with homogeneous well characterized quality will be made available in nearly real time.
EARLINET, the European Aerosol Research Lidar Network, is the first aerosol lidar network, established in 2000, with the main goal to provide a comprehensive, quantitative, and statistically significant data base for the aerosol distribution on a continental scale. At present, 23 stations distributed over Europe are part of the network. The EARLINET-ASOS (Advanced Sustainable Observation System) EC Project, starting on the EARLINET infrastructure, will contribute to the improvement of continuing observations and methodological developments that are urgently needed to provide the multi-year continental scale data set necessary to assess the impact of aerosols on the European and global environment and to support future satellite missions. The main objective of EARLINET-ASOS 5-year project, started on 1 March 2006, is to improve the EARLINET infrastructure resulting in a better spatial and temporal coverage of the observations, continuous quality control for the complete observation system, and fast availability of standardized data products. This will be reached by defining and using common standards for instruments, operation procedures, observation schemes, data processing including advanced retrieval algorithms, and dissemination of data. The expected outcome is the most comprehensive data source for the 4-D spatio-temporal distribution of aerosols on a continental scale.
This paper is a work-in progress report on the development of sol-gel coatings for high power laser systems in the near-UV, infrared region. Silica, titania and titania-silica acid catalysed sols were prepared by using tetraethoxysilane and titanium isoproxide as precursors. Single and multi-layer coatings were generated by dipping on fused silica substrates. The single films were heated at 500°C and 900°C after deposition in order to investigate the role of the sintering temperature either on the optical properties and on the film laser-induced damage threshold at 1064 nm (Nd:YAG c.w. laser) and 351 nm (XeF excimer laser). The ageing effects due to the exposure to humidity was investigated by testing the damp heat resistance of the coatings in agreement with the ISO environmental test for optical coatings. The silica coatings have been assessed before and after the damp heat test with regard to their laser-induced-damage resistance, reflectance and transmittance properties. The optical parameters (refractive index and extinction coefficient) have been determined by UV-VIS-NIR spectrometry. A global fit procedure based on the simultaneous characterisation of several samples was used for the evaluation of the optical properties of the materials both as single films and inside multi-layer stacks.
Mirrors with a graded reflectance profile have been used for many years in unstable cavities for improving the optical quality of the laser output beams. All the variable reflectivity mirrors are realized with multilayer-coatings containing one or more profiled layers inside the stack. They generally exhibit high reflectance in the central area and very low reflectance in the external area. In particular, phase-unifying (PU) mirrors are graded mirrors properly designed in order to obtain a low wave-front distortion in the transmitted laser beam. In this paper, the laser damage resistance properties of a PU mirror designed for XeF excimer lasers (351 nm) have been studied. The laser-induced damage threshold has been measured by a XeF laser on the high and low reflectivity areas. A correlation between the damage threshold values and the standing wave electric field profile, which settles inside the two coating structures during laser irradiation, has been found.
KEYWORDS: Mirrors, Reflectivity, Reflectors, Gas lasers, Laser resonators, Optical components, Near field optics, Ion beams, Thin films, Sputter deposition
Multiple spot mirrors are non-conventional optical components which present a number of equally spaced circular spots with a high reflectance that decreases to zero outside the spots. It is believed that the use of multiple spot mirrors as full reflectors in plane-parallel laser cavities should allow to improve the laser beam optical quality and get a good fillimg of the active medium. A double-spot mirror and a four-spot mirror for a XeCl laser cavity (λ = 308 nm) have been fabricated by depositing HfO2 and SiO2 thin films by reactive ion beam sputtering. The design employed allows to obtain a maximum reflectance (79%) on the spot area and a reflectance lower than 0.5% outside the spots by shaping the thickness of one of the inner layer. To this aim, a properly shaped mask was put inside the vacuum chamber during the deposition of the graded layer. The realization and the optical characterization of these devices are presented in this paper.
Phase-unifying mirrors used as output couplers of laser resonators allow to improve the output laser beam divergence. In this paper, a phase-unifying unstable cavity has for the first time been applied to a high-power, commercially available XeF laser (Lamda Physik 210 i), and a laser output beam of 280 mJ, of 30 ns duration (FWHM), and with a divergence close to the diffraction limited value has been obtained at λ = 351 nm.
We report in this paper lidar measurements of two events of transport of dust from the Sahara region to the Mediterranean Sea, observed in Lecce, Italy (40°20'N,18°06'E). The observations have been made in the framework of the EARLINET project, in which aerosol measurements are performed in all Europe by 21 stations on a coordinate basis. Lidar measurements are compared with informations available from other sources. General results for the lidar ratio are also presented.
The return Raman Lidar signal contains a strong elastically scattered component (at X) that is useful for profiling clouds and aerosols and also weaker inelastically scattered components that provide chemical-specific information. For profiling water vapor, we use components produced by vibrational Raman effect that produces energy shifts characteristic of the molecules in the atmosphere (3652 cm' for water vapor, 233 1 cm1 for nitrogen). The aim of this paper is to process lidar backscattered signal that contains water vapor and aerosol information in order to improve their recovery. Since they are affected by different kinds of noise, an appropriate filtering, with an improved recovery, represents a way to get good estimates of the above components. Water vapor and aerosols are two significant atmospheric components that are generally detected for a better knowledge of weather and climate. In spite of optical filters included in the experimental apparatus used for this paper, there is a need of further filtering, by using signal digital filtering. To discriminate noises from the main signal that is backscattered from sky, we are investigating on the use of appropriate digital filtering to be utilized in order to retrieval a noiseless signal. This approach is different from the current one that uses a poissonian averaging of collected data. In our investigation, we prefer to employ filters that preserve either amplitude information or phase one. Different kinds of filtering procedures have been used in order to isolate the main signal from noise.
A XeF (351 nm) Raman lidar has been used to monitor tropospheric aerosols over the Sallentum peninsula of Italy and the vertical profile measurements of the aerosol extinction and backscatter coefficient and of the lidar ratio are presented in the paper. The measurements have been performed on a fixed schedule along one year and reveal that the aerosols are confined to lower altitudes and are characterized by larger lidar ratio values during autumn and winter months.
The laser induced damage in optical coatings plays a limiting role in the laser reliability. Either the laser cavity mirrors and the optical components employed outside the cavity are often damaged by the laser radiation, delivered by high power lasers. Their resistance becomes more critical at shorter wavelengths, therefore the research is focused on the ultraviolet region where excimer lasers are finding many applications. Laser damage studies were performed at 248 nm (KrF laser) and 308 nm (XeCl laser) on MgF2, HfO2 and SiO2 films and multilayer coatings. Results about the dependence of the damage threshold on both the deposition technique and standing-wave electric field profile inside the coating, are reported.
The aim of this work is to investigate the influence of the standing-wave electric field profile on the laser damage resistance of HfO2 thin films. To this end, HfO2 thin films of different optical thickness and deposited by the electron beam evaporation technique at the same deposition conditions have been analyzed. Laser damage thresholds of the samples have been measured at 308 nm (XeCl laser) by the photoacoustic beam deflection technique and microscopic inspections. The dependence of the laser damage threshold on the standing-wave electric field pattern has been analyzed.
The ion beam assistance during the film growth is one of the most useful method to obtain dense film along with improved optical and structural properties. Afnia material is widely used in optical coating operating in the UV region of the spectrum and its optical properties depend on the production method and the physical parameters of the species involved in the deposition process. In this work afnia thin films were evaporated by an e-gun and assisted during the growth process. The deposition parameters, ion beam energy, density of ions impinging on the growing film and the number of arrival atoms from the crucible, have been related to the optical and structural properties of the film itself. The absorption coefficient and the refractive index were measured by spectrophotometric technique while the microstructure has been studied by means of x-ray diffraction. A strictly correlation between the grain size, the optical properties and the laser damage threshold measurements at 248 nm was found for the samples deposited at different deposition parameters.
The photoacoustic beam deflection technique at (lambda) equals 248 nm was employed for the measurement of the laser damage threshold of single films of magnesium fluoride deposited on superpolished calcium fluoride and fused silica substrates. Different samples were investigated. All films have similar thickness but are deposited by various techniques in different laboratories. The samples are fully characterized, both from the optical and the structural point of view, in the framework of a European Project on 'UV-coatings'. The results of these measurements are reported, along with the data on laser damage threshold, to find out which are the most significant parameters for laser applications.
The joint effect of structural properties and electric field distribution on the laser damage threshold of HfO2 thin films is investigated in this work. Hafnium dioxide thin films of different optical thicknesses and with different structural properties have been realized employing two different deposition techniques: ion-assisted electron beam evaporation and dual-ion-beam sputtering technique. Laser damage thresholds of the sample have been measured at 308 nm by the photoacoustic beam deflection technique. It will be shown that samples presenting lower packing densities and lower peak values of the electric field intensity have higher damage threshold.
We report on water vapor and Ozone measurements made by a Raman LIDAR system recently built up in Lecce, Italy (40 degrees 20'6' N, 18 degrees 6'41' E). The system uses an excimer laser at 248 nm and detects the Raman backscattered radiation from O2, N2 and H2O and can operate in daytime. Atmospheric transmission function, which is mainly due to Ozone absorption, is found not to vary significantly at the operative LIDAR range (200 - 1000 m). We report two cases of daily evolution of water vapor.
SiO2 and HfO2 thin films have been deposited on polished fused silica substrates by the ion assisted electron beam evaporation technique in different deposition conditions. The role of the assisting ion beam parameters either on the otpical and structural film properties and the film damage threshold at 308 nm has been investigated. Laser damage thresholds have been determined by the photoacoustic mirage technique.
Simulated Raman scattering in H2 has been investigated with circularly, linearly, and randomly polarized XeCl laser pulses by varying H2 pressure. The effects of pump radiation polarization and focusing geometry on Raman conversion to rotational and vibrational lines have been investigated. It is shown that circularly polarized pump pulses, high-angle focusing geometries, and/or Raman medium pressures favor the conversion to purely rotational lines, as a consequence of gain suppression effects on vibrational scattering.
The evolution of the main parameters of the intracavity laser radiation oscillating in a Gaussian-cavity applied to a XeCl laser, has been experimentally investigated. It has been found that the temporal evolution of the main laser beam parameter was well approximated by the evolution of a Shell-Gaussian model beam propagating in a bare Gaussian cavity, even if the intensity profiles of the oscillating radiation were quite affected by XeCl laser gain characteristics.
Excimer lasers in conjunction with Raman shifting techniques have commonly been used to get a multi-wavelength laser source for sounding of tropospheric and stratospheric ozone by differential absorption lidar (DIAL) systems. Stimulated vibrational Raman scattering in high-pressure gases as H2 and D2 has generally been used for shifting the output of high power excimer lasers to different wavelengths. In this paper it is shown that the stimulated rotational Raman scattering (SRRS) can also be efficiently employed to get laser radiation at the wavelengths required for DIAL measurements. In particular the first rotational Stokes generated by stimulated Raman scattering in H2, pumped by a XeCl excimer laser at 308 nm, is at 314 nm, and the wavelength pair 308 nm/314 nm may be quite suitable for DIAL measurements of stratospheric ozone. The experimental conditions to optimize the Raman conversion to the first rotational Stokes are found in this paper, demonstrating that energy conversion efficiencies as high as 38% are obtainable with circularly polarized pump radiation.
The dependence of the output laser beam characteristics on the magnification factor of supergaussian unstable resonators applied to a XeCl laser has been investigated. It has been found that high magnification factors and supergaussian mirrors with a high peak reflectivity are required to get a good mode control of the laser oscillating radiation.
Mode locking of a laterally UV prelonized discharge XeC1 laser
has been obtained by using a phase conjugate mirror as full reflector
in the laser cavity. The phase conjugate mirror via stimulated Brilbum
scattering presents a time dependent reflectivity. It acts as a
modulator and provides amplitude modulation at the cavity round trip
time. An output beam made of 5 short pulses separated by 10 nsec has
been obtained. The shortest pulse is 2 nsec FWHM long.
We report the synthesis of surface nitrides by multipulse XeC1 exciTaer laser irradiation in ambient NH3 atmosphere of metal (Ti Mo) and semiconductor (Si Ge) samples. The amount of nitride formed was shown to depend under various extents on the kind of sample the incident laser fluence and the number of subsequent laser pulses. The nitridation process is very sensitive to the oxygen presence. It was evidenced that only traces of oxygen were sufficient for promoting the formation of oxides and oxynitrides. 1.
A compact XeCl laser system made up of an oscillator and an amplifier is described. By applying a stimulated Brillouin scattering mirror (SBSM) to the amplifier, an output laser beam of optical and spectral characteristics very close to those of the oscillator has been obtained. By applying to the amplifier a phase conjugate cavity, 1.7m long, formed by an SBSM and a quartz flat window, a pulse train made of pulses separated by the cavity round trip time has been obtained. The first pulse was 8 nsec long while the last pulse was shorter than 2 nsec.
The operation of a narrow-bandwidth Self Filtering Unstable Resonator
(SFUR) of magnification I M I = 10 applied to a UV-preionized XeC1 laser has
been demonstrated. An intracavity grating (2400 lines/mm)) at a grazing
incidence angle (80 ) has been employed to get a narrow-bandwidth SFUR. A
4.5 mm diameter output beam of 100 pJ, 19 ns long and with a linewidth of
0. 13 A has been obtained. Measurements of the spectral and optical laser
radiation characteristics are reported. The narrow-bandwidth SFUR operation
has been compared with the operation of a plane-plane cavity employing the
same grazing incidence grating and 1 mm diameter intracavity spatial
apertures.
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