Sharp atomic and ionic line spectra of excimer-laser-induced ablation plasmas of samples in liquids were observed. A new double-pulse technique employing quartz fibers facilitates spectral analysis of samples in liquids in which spectral lines normally are strongly broadened and quenched. The first pulse generates a cavitation bubble on the sample surface, which provides a gaseous environment for optical emission spectroscopy on the ablation plasma induced by a second pulse fired into the bubble.

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To determine the temporal evolution of laser induced tissue ablation, arterial wall specimens with either hard calcified or fatty plaques and normal tissue were irradiated in a 0.9% saline solution using a XeCl excimer laser (wavelength 308 nm, energy fluence 7 J/cm2, pulse width 30 ns) through a 600 microns fused silica fiber pointing perpendicular either at a 0.5 mm distance or in direct contact to the vascular surface. Radiation of a pulsed dye laser (wavelength 580 nm) was used to illuminate the tissue surface. The ablation process and the arising bubble above the tissue surface were recorded with a CCD camera attached to a computer based image-processing system. Spherical cavitation bubbles and small tissue particles emerging from the irradiated area have been recorded. The volume of this bubble increased faster for calcified plaques than for normal tissue.

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An arrangement for determining the size distribution of small particles (e.g., droplets or bubbles) is presented. It consists of taking high speed holograms with a frequency doubled Nd:YAG laser, reconstructing the real image with an argon-ion laser, and a digital image processing system with a random access image dissector camera and two cascaded computers for filtering, segmentation, and higher recognition tasks. Results are presented for cavitation bubbles as test objects. It is shown that the quality of the holograms is sufficient for detecting bubbles with a diameter of <20 mum by digital image processing with the present configuration.