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We report on Time-of-Flight Mass Spectrometry (TOFMS) analysis of plasmas produced in laser ablation of Al targets. We used both the second (532 nm) and third (355 nm) harmonic of a Nd: YAG laser system, carrying out the investigation in a regime of relatively high laser fluence (up to 70 J/cm(2)), where the production of ionized species in the plume is maximized. We present TOF mass spectra of ions in the laser-produced plasma, and a detailed analysis of the relative abundance of different charged species as a function of the laser fluence. The presence of single, doubly and triply ionized Al atoms has been observed and the fluence threshold for their production is reported. We also studied the total ion and electron yield at different laser fluences, its saturation above specific energy densities, and singly ionized cluster-ions produced in the laser plasma.

We report on the calculation of the effective telescope area in lidar applications by a ray-tracing approach. This method allows one to consider the true experimental working conditions and hence to obtain accurate values of the effective telescope area as a function of the height. This in turn allows the retrieval of the signal from the ranges where the overlap function is not constant (e.g., lower ranges), thus increasing the useful range interval. Moreover, we show that the spherical mirrors are more appropriate than the parabolic ones for most of the lidar measurements, although a particular alignment procedure, such as the one we describe, must be used. (C) 1998 Optical Society of America.

In a lidar system an accurate transmitter-receiver alignment is essential for correct results. Usually this optical adjustment is time consuming and requires the intervention of highly qualified personnel. As a solution to this problem, a fast and precise automatic alignment procedure is presented, based on a simple model of the transmitter-receiver overlap. The lidar mounted at the Naples University is used to test this method. A centering precision of few microradians is obtained through dedicated software controlling a gimbal-mounted mirror. The automatic alignment procedure is then assessed. In particular, the correctness of the center and of its error is determined. Finally, the system is applied to the monitoring of tropospheric aerosols, leading to the continuous retrieval of profiles with fine spatiotemporal resolution.

A new multiparametric lidar system spanning from UV to mid IR is presently under testing. The system is based on twoOptical Parametric Amplifier (OPA) lasers pumped by a Nd:YAG laser operating at a maximum pulse repetition rate of 100Hz. OPA lasers represent a new design for coherent radiation sources continuously tunable in the UV - JR range. The largerange of tunability of OPA lasers allows to perform Differential Absorption Lidar (DIAL) measurements in a spectral regionwhere most of atmospheric pollutants display absorption lines. The system has been designed to deliver simultaneously in theatmosphere the Nd:YAG fundamental and its harmonics (II and III) as well as the four output beams of the two OPA lasers.The return signals, collected by means of two Newtonian telescopes, can be used to retrieve information on: atmosphericaerosols, water vapour and pollutants concentration, atmospheric temperature, density and transmissivity profiles. In thispaper a detailed description of the system is reported. Moreover, some results obtained by a multiparametric system (basedon a Nd:YAG pumped dye laser) are reported to show the capabilities of a multiwavelength lidar system.Keywords: Lidar, OPA laser, JR.

An accurate transmitter-receiver alignment of a lidar system is essential to obtain correct results. At same time, the effective telescope area can influence the lidar returning signal, especially at the low range. In order to solve this problem, a fast and precise automatic alignment and data correction lidar system is presented, based on a emission-detection overlap model and ray tracing method. Using it we can get an aligned and whole range corrected lidar signal. A centering precision of few mrad has been obtained through a dedicated software automatic controlling a gimbals-mounted mirror. In particular the correctness of the center and of its error has been determined. While through the effective telescope area correction, we got the atmosphere parameter as low as 60m from the telescope. This system has been used in single wavelength direct detection mode and in tunable two-wavelength DIAL measurement. They were respectively applied for continuous monitoring of tropospheric aerosols and continuous measurement of the NO 2 .

The present paper is devoted to the description of two distinct multiparametric lidar system presently under development. The first system is based on a Nd:YAG laser pumping a dye laser equipped with a dual wavelength device. The second lidar system is based on two optical parametric oscillator (OPO) lasers pumped by a Nd:YAG laser operating at a pulse repetition rate of 100 Hz. OPO lasers represent a new design for coherent radiation sources continuously tunable in the UV -- near IR range (up to 2 micrometer). This allows us to perform differential absorption lidar (DIAL) measurements in a spectral region where most of atmospheric pollutants display absorption lines. The selection of the wavelengths to be used for DIAL measurements is a non trivial task. In particular, a method to select the optimal (lambda) ON and (lambda) OFF has been developed and applied to several molecular gases. Both systems have been designed to carry out simultaneous measurements of atmospheric aerosols, water vapor profiles, temperature and density profiles, atmospheric transmissivity, and atmospheric pollutants concentration.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We have characterized experimentally the trapping of resonance radiation in an effusive He beam produced by a needle injector. In order to take into account the influence of secondary effects, such as collisions, on the trapping process, the measurements were carried out by investigating the line intensity dependence on the atomic density of transitions , and in the visible and and in the vacuum ultraviolet region of the helium spectrum. The comparison between visible and vacuum ultraviolet spectra allowed us to characterize the excitation process and to evaluate the contribution of collisional effects. We have calculated the escape factor, g, as a function of the atomic density and of the distance from the needle injector, i.e. along the beam path. The results were also compared with the Holstein and Phelps approach describing the trapping process in terms of an effective radius, . Our results show that in the case of an effusive beam, the effective radius is of the order of the effusive beam radius, namely .

A lidar system with the characteristic of simultaneously monitoring several atmospheric parameters such as atmospheric aerosols load, water vapor content, temperature and density, atmospheric transmissivity, and atmospheric pollutants concentration, has been realized. This system, based on two OPA lasers pumped by a Nd:YAG laser operating at maximum repetition rate of 100 Hz, is primary dedicated to tropospheric measurements. The system is continuously tunable over the spectral range 410 nm - 2500 nm, allowing DIAL measurements in a region where most of atmospheric pollutants display absorption lines. Preliminary measurements have been carried out. We report the simultaneous temporal evolution of the aerosol backscattering coefficient profiles at 355 nm and 829 nm in a rural area. A method to select optimal couples of wavelength for DIAL measurements in the near/mid IR spectral region has been developed. A sensitivity analysis has been carried out in order to find the minimum detectable concentration, that has been demonstrated of the order of few tenths up to few part per million in volume.