Dual-wavelength dispersion characterization of confocal Fabry-Perot interferometers.

Optical resonators simultaneously resonating at different wavelengths are of interest in passive as well as active optical cavities. Dual-wavelength lasers, optical parametric amplifiers and spectrometers, e.g., in high spectral resolution lidar (HSRL) are effectively improved by employing multiply resonant cavities. In particular, HSRL allows us to measure aerosol optical properties without a priori hypotheses. Here we analyze optical dispersion in a HSRL prototype, based on a confocal Fabry-Perot interferometer (CFPI), developed to work at 532 nm (the lidar excitation wavelength). The presence of dispersion should be accounted for when realizing an effective HSRL because a second beam is required to obtain sufficient locking stability. We have performed an experiment in order to measure the dispersion contributions coming from cavity mirror coating and air and evaluate the stability of the transmission peaks in order to optimize the performances of HSRL.

Expectation maximization and the retrieval of the atmospheric extinction coefficients by inversion of Raman lidar data.

We consider the problem of retrieving the aerosol extinction coefficient from Raman lidar measurements. This is an ill-posed inverse problem that needs regularization, and we propose to use the Expectation-Maximization (EM) algorithm to provide stable solutions. Indeed, EM is an iterative algorithm that imposes a positivity constraint on the solution, and provides regularization if iterations are stopped early enough. We describe the algorithm and propose a stopping criterion inspired by a statistical principle. We then discuss its properties concerning the spatial resolution. Finally, we validate the proposed approach by using both synthetic data and experimental measurements; we compare the reconstructions obtained by EM with those obtained by the Tikhonov method, by the Levenberg-Marquardt method, as well as those obtained by combining data smoothing and numerical derivation.

[Not Available]. / Valutazione del rischio da esposizione al rumore in un'officina meccanica e scelta dei dispositivi di protezione uditiva.

In this study the authors intended to describe and provide a critical remark of the necessary assessments for the selection of the most appropriate personal protective equipment. This selection has been made with reference to the calculation methods specified in the International Standard UNI EN ISO 9612 and UNI EN 458.

Retrieval of aerosol extinction-to-backscatter ratios by combining ground-based and space-borne lidar elastic scattering measurements.

A technique to determine the aerosol extinction-to-backscatter ratio (lidar ratio) as well as extinction and backscatter coefficients from simultaneous ground-based and space-borne lidar measurements is proposed. This technique can be applied in presence of more than one aerosol layer. To test the reliability of this technique, a numerical simulation has been performed. Moreover, the technique has been applied to an actual case by analyzing data from Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) and Napoli-Earlinet lidar measurements. The results show that the values of lidar ratio and backscatter coefficient retrieved by this technique are in good agreement with the ones obtained from Raman measurements.

Detection of fluorescent nanoparticles in flame with femtosecond laser-induced fluorescence anisotropy.

The mean size of fluorescent nanoparticles produced in a propane flame has been measured with an in-situ technique employing a femtosecond laser to excite the sample and a streak camera for time-resolved detection of the fluorescence. The time profile of the fluorescence anisotropy showed a Gaussian behaviour, typical of free rotor reorientation. By measuring its width, we estimated an average carbon particle diameter of 3.3 nm, thus confirming the existence of combustion produced nanoparticles. The technique proves to be applicable to the study of gas-phase nanoparticles, both in combustion and environmental studies.

Retrieval of atmospheric particles optical properties by combining ground-based and spaceborne lidar elastic scattering profiles.

A simple algorithm is derived to retrieve the aerosol backscattering and extinction vertical profiles from simultaneously detected ground and space elastic lidar signals, without any a priori hypothesis on aerosol particles properties. This technique can be applied at any wavelength whenever two "counter looking" lidars are available and the atmosphere can be considered horizontally homogeneous in a spatial scale of the order of the distance between the two lidar beams. To test the accuracy of the algorithm a numerical simulation has been performed. Moreover, it has been applied in a real case to level 1 products from CALIPSO.

Insights on Clusters Formation Mechanism by Time of Flight Mass Spectrometry. 1. The Case of Ethanol-Water Clusters.

In the present work, water clusters with the addition of an electrophilic molecule such as ethanol have been studied by time of flight mass spectrometry (TOFMS). Mass distributions of molecular clusters of ethanol, water, and ethanol-water mixed clusters were obtained by two different ionization methods: electron ionization (EI) and picosecond laser photo-ionization (PI) at a wavelength of 355 nm. It was shown that short pulse laser ionization increases the signal intensity and promotes the extension of the detected mass range of the clusters in comparison with EI. Much larger clusters were detected in our experiments with respect to the current literature. The autocorrelation function (AF) was introduced in the analysis of the composition of the water clusters in terms of fundamental periodicities for obtaining information on clusters formation mechanisms. Besides, it was found that ethanol molecules are capable of substitutional interaction with hydrogen-bonded water clusters in ethanol-water binary mixtures but the self-association of ethanol was the dominant process. Moreover, the increase of ethanol concentration promotes both the formation of hydrated ethanol clusters and the self-association of ethanol clusters in ethanol-water binary mixtures. The formation of water-rich clusters and subsequent metastable fragmentation were found to be the dominant processes determining the water-rich cluster distribution, irrespective of the ionization process, while the ionization process significantly affects the ethanol-rich cluster distribution.

Analysis of polycyclic aromatic hydrocarbon sequences in a premixed laminar flame by on-line time-of-flight mass spectrometry.

A time-of-flight mass spectrometer in reflectron configuration has been used for the real-time detection of combustion products. The products of a premixed laminar C2H4/O2 flame at atmospheric pressure were sampled along its axis, diluted with inert gas and carried to the ion source as a molecular beam under minimal perturbation. Electron ionization and different optical ionization sources are compared. Photoionization was achieved with laser radiation from a Nd:YAG nanosecond pulsed laser at two different wavelengths in the UV range (266 and 355 nm). The mass spectra obtained using laser wavelength of 355 nm and electron ionization present a series of ions regularly spaced by 18 m/z units up to m/z 2000. This series allowed precise calibration of the instrument for compounds of high molecular weight. Information on the chemical nature of the analyzed species has been obtained by comparing mass spectra produced with different ionization methods. In order to better understand the growth mechanisms, polycyclic aromatic hydrocarbon sequences have been analyzed by fast Fourier transform of the mass spectra.