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Attempts to achieve Q-switching of Er:YAG lasers through the use of PLZT ceramic modulators, are reported. PLZT ceramics exhibit pronounced quadractic electrooptic effect. Experiments were undertaken with the commercial ERY-1 ISKRA elektrooptika laser. The great electrooptic effect in PLZT enables attractively small elements to be built for the purpose.

The absorption and transport scattering coefficients of biological tissues determine the radial dependence of the diffuse reflectance that is due to a point source. A system is described for making remote measurements of spatially resolved absolute diffuse reflectance and hence noninvasive, noncontact estimates of the tissue optical properties. The system incorporated a laser source and a CCD camera. Deflection of the incident beam into the camera allowed characterization of the source for absolute reflectance measurements. It is shown that an often used solution of the diffusion equation cannot be applied for these measurements. Instead, a neural network, trained on the results of Monte Carlo simulations, was used to estimate the absorption and scattering coefficients from the reflectance data. Tests on tissue-simulating phantoms with transport scattering coefficients between 0.5 and 2.0 [mm.sup.-1] and absorption coefficients between 0.002 and 0.1 [mm.sup.-1] showed the rms errors of this technique to be 2.6% for the transport scattering coefficient and 14% for the absorption coefficients. The optical properties of bovine muscle, adipose, and liver tissue, as well as chicken muscle (breast), were also measured ex vivo at 633 and 751 nm. For muscle tissue it was found that the Monte Carlo simulation did not agree with experimental measurements of reflectance at distances less than 2 mm from the incident beam. Key words: Tissue optics, reflectance, Monte Carlo, neural network.

We investigate why vessels that contain blood, which has a red or a dark red color, may look bluish in human tissue. A CCD camera was used to make images of diffusely reflected light at different wavelengths. Measurements of reflectance that are due to model blood vessels in scattering media and of human skin containing a prominent vein are presented. Monte Carlo simulations were used to calculate the spatially resolved diffuse reflectance for both situations. We show that the color of blood vessels is determined by the following factors: (i) the scattering and absorption characteristics of skin at different wavelengths, (ii) the oxygenation state of blood, which affects its absorption properties, (iii) the diameter and the depth of the vessels, and (iv) the visual perception process.

During 40 years of laser research, a variety of systems have been tested for caries removal and cavity preparation, but up to now only Erbium lasers have achieved clinical importance. Based on a thermomechanical ablation process, these lasers offer not only a high efficiency but also low thermal and mechanical side effects, which are a prerequisite for painless treatments. A number of clinical studies and daily practical applications have proven Erbium lasers to be safe and nearly painless. In the future, lasers are not expected to replace the bur, but will allow a less invasive "smart" dentistry. [ABSTRACT FROM AUTHOR]

The effect of pulsed laser irradiation on the structural and magnetic properties of NiMn/Co thin films is examined. The increase in the exchange bias field for laser irradiated samples is attributed to the increased grain size and the improved (111) texture of the NiMn layer after laser irradiation.