Qualitative and quantitative investigation of chromium-polluted soils by laser-induced breakdown spectroscopy combined with neural networks analysis.

Laser-induced breakdown spectroscopy (LIBS) has been applied to the analysis of three chromium-doped soils. Two chemometric techniques, principal components analysis (PCA) and neural networks analysis (NNA), were used to discriminate the soils on the basis of their LIBS spectra. An excellent rate of correct classification was achieved and a better ability of neural networks to cope with real-world, noisy spectra was demonstrated. Neural networks were then used for measuring chromium concentration in one of the soils. We performed a detailed optimization of the inputs of the network so as to improve its predictive performances and we studied the effect of the presence of matrix-specific information in the inputs examined. Finally the inputs of the network--the spectral intensities--were replaced by the line areas. This provided the best results with a prediction accuracy and precision of about 5% in the determination of chromium concentration and a significant reduction of the data, too.

Laser-induced breakdown spectroscopy of composite samples: comparison of advanced chemometrics methods.

Laser-induced breakdown spectroscopy is used to measure chromium concentration in soil samples. A comparison is carried out between the calibration curve method and two chemometrics techniques: partial least-squares regression and neural networks. The three quantitative techniques are evaluated in terms of prediction accuracy, prediction precision, and limit of detection. The influence of several parameters specific to each method is studied in detail, as well as the effect of different pretreatments of the spectra. Neural networks are shown to correctly model nonlinear effects due to self-absorption in the plasma and to provide the best results. Subsequently, principal components analysis is used for classifying spectra from two different soils. Then simultaneous prediction of chromium concentration in the two matrixes is successfully performed through partial least-squares regression and neural networks.

Nondestructive analysis of the transverse structure of novel optical fibers by third-harmonic-generation microscopy.

We demonstrate the suitability of the third-harmonic-generation technique as a new nonlinear microprobe for nondestructive determination of the index profile of optical fibers. Photonic bandgap (Bragg-type) and air-silica microstructure (ASM) fibers were tested. The complete spatial characteristics, such as hole diameter and spacing into ASM fibers or sandwiched layer thickness into Bragg fibers, were demonstrated to be attainable anywhere along a bare fiber.

Nonlinearity measurements of thin films by third-harmonic-generation microscopy.

We show that the electronic part of the nonlinear susceptibility chi(3) of thin films can be easily measured by third harmonic microscopy. The phenomenon of third harmonic generation (THG) is excited by a femtosecond laser beam focused at the interface between the thin film and a reference layer. The value of chi(3) is deduced from the THG intensity measurements with the help of a classical model. The validity of this simple and alternative method is established by testing reference liquid films.

Imaging of Ca(2)+ intracellular dynamics with a third-harmonic generation microscope.

We describe the promising development of third-harmonic generation (THG) in laser scanning microscopy for study of the functional imaging of live biological cells. The dynamics of Ca(2+) in biological cells is shown. The Ca(2+) signal consists of a transient increase in the intracellular concentration. THG microscopy allows one to temporally visualize the release of Ca(2+) from internal stores and (or) calcium influx.

Planar waveguides formed by Ag+-Na+ ion exchange in nonlinear optical glasses: diffusion and optical properties.

All-optical communication systems are the subject of intense research related to the integration of nonlinear optical materials. In sodiocalcic borophosphate glasses that contain niobium oxide and exhibit high nonlinear optical indices, planar waveguides have been formed by a Ag(+)-Na(+) ion-exchange technique. WKB analysis has been used to characterize the diffusion profiles of silver ions exchanged in glass substrate samples chemically by an electron microprobe technique and optically by an M-line technique. These methods permit the Ag(+) penetration depth and diffusion profile shape and index profiles to be determined. The results are analyzed and discussed in relation to Ca(2+) concentration and exchange conditions in glasses. The Ag(+) diffusion in these glasses can be almost entirely controlled for index-profile engineering.

Measurements of complex third-order optical susceptibility in a collinear pump-probe experiment.

We demonstrate simultaneous measurement of the real and the imaginary parts of third-order susceptibilities by use of a collinear pump-probe technique. This technique allows for good results and simple implementation. The signal analysis is based on the particular oscillatory signature versus the pump-probe delay allowed by the collinear configuration. Results are compared with interferometric measurements of a SF59 (Schott) glass sample.

Experimental study of the injection-locked continous-wave ring dye laser.

We present the first reported experimental study of the properties andcharacteristics of the injected cw ring dyelaser together with a new method of injection locking for cw sources. The injection thresholds and the intracavity powers below and above threshold have been investigated as a function of the pump power, the injecting radiation power, and the frequency detuning. The experimental results, in good agreement with a theoretical analysis previously proposed, demonstrate the possibility to obtain higher single-frequency powers.