Mapping and elemental fractionation of aerosols generated by laser-induced breakdown ablation.

Laser-induced breakdown spectroscopy (LIBS) has been used to map the distribution of particulate matter inside the plume created by laser ablation of a brass target. The spatial density distribution of the different components of the plume was determined in an attempt to reveal the mechanism of fractionation in the process of the laser ablation. In this experiment two Nd:YAG pulsed lasers were used. The first beam was focused on the target to generate a plume after breakdown of the surface. The second laser was focused on the plume and generated the second breakdown. The composition of the region probed by the second beam was determined by analyzing the spectral emission from the second breakdown. By scanning the probe time and position, the temporal and spatial evolution of the laser ablative plume could be discovered. Spatial and temporal fractionation was observed in brass plume.

Schlieren systems with coherent illumination for quantitative measurements.

Schlieren systems with a coherent light source were investigated by the Fourier optics technique. The imaging properties of the systems with various cutoff filters were studied. Systems with a graded piecewise linear filter and a Gaussian step function convolution (graded) filter are considered, demonstrating that the image can be approximated by the geometrical-optics theory of conventional schlieren systems. A nonlinear phase contribution was estimated, allowing for the measurement of strong phase objects. Within the framework of linear approximation the results are described by the phase derivative point-spread function, introduced in this paper as the schlieren point-spread function. In addition, modification of the Lopez cutoff filter is proposed, demonstrating its superiority over the piecewise linear and the Gaussian step convolution filters. Simulations of coherent schlieren imaging as well as phase derivative measurements were performed. Finally, the imaging properties of the schlieren systems with the different filters are compared.

Heterodyne schlieren system.

A new heterodyne technique for the quantitative analysis of schlieren images is described. The technique is based on phase measurements of signals generated by a photodetector observing the variations in light intensity caused by a traveling grating of slits located at the knife-edge plane of a conventional schlieren system. The phase of the signal is proportional to the displacement of the slit image on the knife-edge plane as a result of the light deflection passing through a phase object. The displacement is proportional to the ray deflection angle and hence to the local gradient of the index of refraction. The technique, which is quantitatively precise and sensitive, is demonstrated by measurement of deflections caused by a lens with a focal length of f = 20 m. A displacement of 0.22 mm and a deflection of an angle of 5.2 x 10(-4) rad were detected.