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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.

Glyoxal (CHOCHO), as an indicator of photochemical “hot spots”, was for the first time the subject of a differential absorption lidar (DIAL) campaign. The strongest absorption line of glyoxal in the blue wavelength region – 455.1 nm – was chosen as the experimental absorption wavelength. In order to handle the effects of absorption cross-section variation of the interfering gas – nitrogen dioxide (NO2) – three-wavelength DIAL measurements simultaneously detecting glyoxal and NO2, were performed. The differential absorption curves, recorded in July 2012, indicate an extremely low glyoxal concentration in Lund, Sweden, although it is expected to be peaking at this time of the year.© (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only. (Less)

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 lid ar 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 quantifica tion 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 si nce June 2006. A strategy for correlative measurements has been defined on the base of the analysis of the high re solution ground track data provid ed by NASA. Results in terms of comparisons between EARLINET and available CALIPSO pr oducts, both level 1 and level 2 data, are presented. Keywords: Lidar, aerosol, clouds, EARLINET, CALIPSO

Coordinated lidar observations of Saharan dust over Europe are performed in the frame of the EARLINET-ASOS (2006-2011) project, which comprises 25 stations: 16 Raman lidar stations, including 8 multi-wavelength (3+2 station) Raman lidar stations, are used to retrieve the aerosol microphysical properties. Since the launch of CALIOP, the two-wavelength lidar on board the CALIPSO satellite (June 2006) our lidar network has been performing correlative aerosol measurements during CALIPSO overpasses over the individual stations. In our presentation, we report on the correlative measurements obtained during Saharan dust intrusions in the period from June 2006 to June 2008. We found that the number of dust events is generally greatest in late spring, summer and early autumn periods, mainly in southern and south-eastern Europe. A measurement example is presented that was analyzed to show the potential of a ground based lidar network to follow a dust event over a specific study area, in correlation with the CALIOP measurements. The dust transport over the studied area was simulated by the DREAM forecast model. Cross-section analyses of CALIOP over the study area were used to assess the model performance for describing and forecasting the vertical and horizontal distribution of the dust field over the Mediterranean. Our preliminary results can be used to reveal the importance of the synergy between the CALIOP measurement and the dust model, assisted by ground-based lidars, for clarifying the overall transport of dust over the European continent.

Routine lidar measurements of the aerosol vertical distribution have been performed over Athens, Greece using a multi-wavelength (355-387-407-532-607-1064 nm) Raman lidar system, since 2006 in the frame of the EARLINET-ASOS (2006-2011) project. Additionally, since June 2006, correlative measurements for CALIOP space-borne lidar are performed. The aim of these measurements is to provide validation profiles for the CALIOP instrument in the lower and middle troposphere (0.5-8 km) in terms of the aerosol backscatter coefficients at 532 nm and 1064 nm, the color ratio (532/1064 nm) and the depolarization ratio at 532 nm, but mainly to provide information about the aerosol extinction profiles and the corresponding lidar ratios at 532 nm. From the available correlative CALIOP level-2 and multi-wavelength Raman lidar aerosol data over Athens, we selected to present cases that have been identified as Saharan dust outbreaks and large biomass burning events, using air mass backward trajectories in order to characterize the source of the aerosols. We found that the vertical profiles of the aerosol optical properties between CALIOP and NTUA lidars were not always in a good agreement during the exact time of the satellite overpass, especially for daytime measurements, when the distance between the two instruments was greater than 40 km. An improvement was noticed when ground-based lidar measurements where performed previously or later than the CALIPSO overpass time. For the nighttime intercomparison the agreement between the two instruments was better during the CALIPSO overpass time. This was attributed mainly to the closer nighttime satellite track over the Athens lidar station.

Conventional solid state laser pumping cavities has been used, after proper modification, in order to achieve efficient laser action by Cr:LiSAF crystals. The crystal samples were placed in the laser head, properly supported for efficient pumping to achieve satisfactory laser action. It has been proved that for a successful result a strong flash pumping source and a low output coupling is needed to help the low overall gain of the small Cr:LiSAF samples.

The crystal field environment of the Ce+3 dopant in LiSrAlF6 (LiSAF) crystals has been studied by the Electron Spin Resonance (ESR) spectroscopic technique. Ce was found in a highly anisotropic trigonal environment which suggests that it substitutes for the Sr site. Na+ ions operate as charge compensators to Ce+3 possessing nearby to Ce, Sr sites. The ground state electronic wavefunction and the energy diagram of Ce are discussed in view of our ESR results.

The iterative (with constant "lidar ratio") and the general recursive (with variable "lidar ratio") algorithms have been used to backscattering lidar data. The data have been collected in the Lidar Center in Thessalonica, Greece. The vertical profiles of backscatter coefficient retrieved with these two algorithms differ slightly. The vertical profile of "lidar ratio" for the laser wavelength 532 nm, depending on the day or time of the day, changes its values but doesn't reveal any essential structure. The wavelength 355 nm seems to be more "sensitive" and shows some structure for "lidar ratio". Most probably these structures are due to the presence of different aerosol layers. From vertical backscatter coefficients, both 355 nm and 532 nm, at least, two aerosol layers can be differentiated.

Both marine and urban aerosols, which differ in their origin and chemical composition, are subjected to strong dynamic processes in the coastal areas, especially over strongly urbanised areas. The simultanteous presence of both types of aerosols leads to their effective mixing due to the action of winds and convection. This work presents examples of interactions of the two types of aerosols and the impact of the dynamic atmospheric processes on migration of aerosol masses, at two locations in Athens and Kolobrzeg.

This paper presents results of a study of aerosol pollution distribution and dynamics measured by lidar observations over the city of Athens. The seasonal dynamics of vertical changes in the backscattering coefficient, extinction coefficient and lidar ratio for lower troposphere has been determined.

Vertical profiles of aerosol extinction and "lidar ratios" of the lower troposphere in Thessalonica have been measured with two -wavelengths lidar. The extinction profile for the wavelength 355 nm seem to be insensitive for the time of the day. The profile for 532 nm has its maximum intensity at about 7 am, then decreases and increases during the afternoon and the evening. The vertical profiles of "lidar ratio" are structured for 355 nm but for 532 nm, are almost constant. It has been concluded that, at least, two different kinds of aerosols contribute to the observed profiles: one sensitive (532 nm) and a second one, insensitive for the changes in solar radiation (355 nm) during the day. Both, extinction and "lidar ratios" are characterized by high values for the wavelength 355 nm.

In this paper we present the basic features of the laser remote sensing (lidar) system located at the National Technical University of Athens (NTUA), Greece. This compact and mobile lidar is in full operation since late 1999. This paper includes basic features of the lidar technique (technical description, temporal and spatial resolution, range etc.), a brief presentation of the instrumentation used and an outline of the algorithms applied to retrieve useful information from the backscattered lidar signals. We also present some examples of aerosol profiling measurements over Athens, which include monitoring of clouds and suspended aerosols (i.e. during Saharan dust and photochemical air pollution events), as well as the evolution of the Planetary Boundary Layer (PBL) over the Greater Athens Area (GAA).

Suspended aerosol particles play a significant role in the Global Change issue. Every year huge quantities of Saharan dust are transported to the European continent and North Atlantic Sea. Since May 1, 2000, an elastic backscatter lidar station is in operation in Athens, Greece, in the frame of the European LIDAR Network (EARLINET), aiming at the monitoring of extreme aerosol events over the Eastern Mediterranean Sea. During the first year of operation 20 cases of Saharan dust transport to the East Mediterranean Sea (EMS), were successfully observed. The lidar data are correlated with meteorological and satellite observations, including the aerosol index (AI data from the Total Ozone Mapping Spectrometer (TOMS) and the SeaWiFS satellite images. The analysis of the data collected so far, made possible a first statistical approach of the vertical and horizontal extent and of the seasonal variation of free tropospheric Saharan dust layers over the EMS area. The main results of this work are: (1) multiple dust layers of variable thickness (0.5 - 4 km) are systematically observed in the altitude region 2 - 6 km, (2) Saharan dust outbreaks take place all year round, with more pronounced frequencies during the summer period and can persist for a few days (1- 5), (3) 24 - 48 hours are usually needed for the Saharan air masses to reach the EMS area, and finally (4) the TOMS AI values can reach 1.5 - 3.5 over Greece. These lidar data gave the aerosol vertical structure over the Eastern Mediterranean Sea during Saharan dust outbreaks and can be a direct input for global radiative transfer models.

A laser laboratory prototype for laparoscopic, endoscopic or angioplastic surgery was developed, incorporating an Er:YAG laser as the therapeutic tool in endoscopic/laparoscopic surgery and angioplasty and a N2 laser induced fluorescence system in order to monitor the surgical process. Additionally, a laser radiation transmission system with waveguides and fibers was developed, to transmit the laser radiation, through an endoscope or laparoscope. The system was used in in vivo animal trials, giving promising results for the application of the device in semi-operative applications, in combination with systems of improved endoscopic imaging.

The paper gives a general inversion algorithm for lidar's data derivation and profiles of the extinction coefficient, backscattering coefficient and lidar ratio for the lower troposphere. To the best of our knowledge these are the first results obtained with this algorithm.

The Lidar technique is an efficient tool for continuous monitoring of clouds and aerosols, with high temporal and spatial resolution. Lidar systems can provide long-term accurate information on cloud top and base heights and their optical depth. The spatial distribution of clouds and the diurnal variation of cloud properties are important parameters in many operational and research applications (i.e. radiative transfer modeling, energy balance, meteorology, etc.). In this paper, we present the application of a compact mobile lidar system in monitoring of cloud properties, over Athens, Greece. Preliminary lidar measurements were performed during summer- autumn 1994, focusing on the study of short-time variability of spectral cloud properties at two wavelengths (355 nm and 532 nm), using a compact Nd:YAG laser. The Lidar dataset acquired is analyzed during selected cases and conclusions are drawn.

A novel backscattering lidar inversion procedure is presented. This method consists of two steps: the first one is the determination of a preliminary vertical profile of the unit volume extinction coefficient by the iterative Klett's method, and the second one is the determination of the vertical profile of unit volume backscattering coefficient from the previous step --using the relationship between (alpha) (r) and (beta) (r) -- which is given by two independent solutions for both variables. The calculation of the vertical profile of the 'lidar ratio' [determined as: (beta) (r)/(alpha) (r) is automatic ]. The proposed method is applied, in a preliminary case, to several backscatter lidar signals, obtained by a two wavelength backscattering lidar system in Greece. The proposed procedure can be applied for each wavelength of a multiwavelength backscattering lidar system, independently -- which means that the unit volume extinction and backscatterer profile of the atmosphere can be spectrally resolved. The general case of this procedure has not been applied yet, to a computer simulation, while this work is still in progress.

The LIDAR technique is an efficient tool for continuous monitoring of air pollution over urban areas, with high temporal and range resolution. The urban areas of Athens, Greece, exhibit high air pollution levels, especially those regarding suspended particulates, mainly linked with car traffic and industrial emissions. In this paper, we present the first mobile Greek LIDAR system, based on the LabVIEW code, now located at the Athens Technical University Campus, nearby the urban area of the city. The LIDAR dataset acquired, under various air pollution and meteorological conditions, gives specific indications of the diurnal variation of the backscattering coefficient and relative backscatter of the suspended particulates in the first 2500 - 3000 m ASL over the city of Athens. The LIDAR dataset acquired is analyzed in conjunction with meteorological data (temperature, humidity) and air pollution data (O3 CO, NOx), acquired at the same site, and conclusions are drawn.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The stimulated Raman scattering (SRS) technique has been sued for upward and downward shifting the 3rd harmonic of a pulsed Nd:YAG laser into the 274-503 nm wavelength region. The gases investigated were hydrogen (H 2 ) and deuterium (D 2 ), using helium (He) as buffer gas. Experimental results on the output Stokes and anti-Stokes conversion efficiencies of the forward SRS technique in H 2 , D 2 and He, versus Raman gas pressure and input pump energy, are presented. Conversion efficiencies more than 40 percent were achieved and the output energies obtained at the various ultraviolet and visible wavelengths were of the order of several mJ.

In the last few years, there has been an increasing interest for the 3.0 micrometers laser radiation, as this wavelength is very strongly absorbed by the water and the other components of soft and hard tissue, in various medical applications, as soft tissue treatment, atherosclerotic plagues removal, treatment of eye lenses, vitreous surgery, hard tissue treatment, bone cutting and drilling, dentistry applications, etc. For all these medical applications reliable lasers emitting in the 3.0 micrometers wavelength range are needed and thus an intensive development effort is going on throughout the world. Our laser development effort, with the Er:YAG and the HF lasers, the only lasers emitting in the 3.0 micrometers wavelength part of the spectrum, in N.T.U.A., is briefly described in this article. For each one of the above possible medical applications, a demand for good flexible delivery systems, for pulsed Er:YAG or continuous wave and pulsed HF laser radiation arises. Several research groups around the world have suggested some possible solutions and among them are sapphire fibers, zirconium fluoride glasses, hollow metallic waveguides, hollow dielectric waveguides, hollow plastic waveguides, etc. In this paper we present the transmission properties of dielectric coated silver hollow glass waveguides fabricated in Japan, dielectric coated quartz waveguides and hollow plastic waveguides fabricated in Israel, sapphire fibers fabricated in USA, and fluoride glass fibers fabricated in France, we compare their straight and bent loss characteristics and we discuss their potential in the above mentioned medical applications.

Pulsed laser ablation is well established as a universal tool for surface processing of organic polymer materials. The polymer ablation efficiency of different laser wavelengths, from 355 nm to 532 nm, is studied for short laser pulses, of nanosecond pulse duration. Ablation rates of polymers have been measured by irradiating the polymers using a pulsed Nd:YAG laser. This laser source produced pulses at the second and third harmonic simultaneously at (lambda) equals 532 nm and (lambda) equals 355 nm. Effective ablation was also observed by irradiating the polymer samples with the Raman-shifted Nd:YAG laser, at (lambda) equals 397.1 nm, in order to investigate comparatively the ablation efficiency at different laser settings. For transparent materials, in the corresponding ablation wavelengths and pulse width, the dependence of the ablation rate on the laser spot diameter and the laser energy fluence has been investigated. In general, the polymers used in this work show a more or less pronounced increase of the ablation rate with decreasing spot diameter for the same fluence, especially in the case of visible laser irradiation.

The development of a novel laser-based seam tracking system for real-time industrial robot welding applications is presented. The system is based on a infrared diode laser, able to scan perpendicularly the seam joint using a laser scanner. A dedicated CCD camera collects the reflected laser light and the relative distance of the surface points under the sensor, form the sensor itself, is then calculated by simple triangulation techniques. The features of the seam profile such as the joint position and geometry are extracted and measured, with a precision of a some microns. In this paper the main components of the novel laser-based seam tracking system will be presented, as well as preliminary results obtained by our system. The laser-based seam tracking system will be of low cost, simple to use a nd rugged enough to provide trouble-free service in any welding or hostile industrial environment. This system will be the first to be developed and installed in Greece.

The diurnal variation of the Planetary Boundary Layer (PBL) structure and of the vertical profiles of the suspended particlates attenuation coefficient, are presented for the case of a semi-rural area near the north-eastern exit of the Athenian basin. These data were obtained using a ground-based LIDAR system operating at 355 nm and 532 nm, during the MEDCAPHOT-TRACE Campaign in the summer of 1994. The LIDAR system was pointing vertically and was operated during various air pollution (low up to severe photochemical episodes) and meteorological conditions (synoptic flow circulation, land-, and sea-breeze circulation). The LIDAR data are intercompared with meteorological and photochemical pollution data obtained by an instrumented aircraft overflying the Athens basin.

The performance characteristics of a novel design, sliding discharge plasma cathode pulsed HF lasers are given and their advantages, as far as laser and tissue interaction is concerned, are analyzed. With these lasers, intense multiline operation in the 2.5 to 3.5 micrometers range is observed from the sliding discharge plasma cathode three electrode system, with a wide cross section beam, good beam profile quality and high efficiency at moderate voltages. These characteristics are very crucial for obtaining reproducible results leading to a well-defined dosimetry in biomedical applications. To the best of our knowledge this is the first report on the HF chemical laser operating in the sliding discharge plasma cathode three electrodes excitation mode and the first time this novel design lasers are being engaged in some laser and tissue interaction applications. With these recently developed, novel design gas lasers, operating in the mid-infrared part of the spectrum, it has become very interesting to examine their efficacy in ablating multicomponent tissues, such as occluded carotide arteries. Some preliminary experimental results are presented and the role of the HF laser in optimization of soft and hard biological tissue ablational treatment is discussed.