Influence of longitudinal mode beating on laser-induced damage in fused silica.

In our study, the laser-induced damage densities on a fused silica surface produced by multiple longitudinal mode (MLM) pulses are found to be higher than those produced by single longitudinal mode pulses at 1064 nm. This behavior is explained by the enhancement of the three-photon absorption due to the intensity spikes related to longitudinal mode beating. At 355 nm, the absorption is linear and an opposite behavior occurs. It can be explained with the help of a process involving thermomechanics coupled with the fine time structure of MLM pulses, leading to the possible annealing of part of the absorbent defects.

Evidence of a green luminescence band related to surface flaws in high purity silica glass.

Using luminescence confocal microscopy under 325 nm laser excitation, we explore the populations of defects existing in or at the vicinity of macroscopic surface flaws in fused silica. We report our luminescence results on two types of surface flaws: laser damage and indentation on fused silica polished surfaces. Luminescence cartographies are made to show the spatial distribution of each kind of defect. Three bands, centered at 1.89 eV, 2.75 eV and 2.25 eV are evidenced on laser damage and indentations. The band centered at 2.25 eV was not previously reported in photo luminescence experiments on indentations and pristine silica, for excitation wavelengths of 325 nm or larger. The luminescent objects, expected to be trapped in sub-surface micro-cracks, are possibly involved in the first step of the laser damage mechanism when fused silica is enlightened at 351 nm laser in nanosecond regime.

Impact of storage induced outgassing organic contamination on laser induced damage of silica optics at 351 nm.

The impact of storage conditions on laser induced damage density at 351 nm on bare fused polished silica samples has been studied. Intentionally outgassing of polypropylene pieces on silica samples was done. We evidenced an important increase of laser induced damage density on contaminated samples demonstrating that storage could limit optics lifetime performances. Atomic Force Microscopy (AFM) and Gas Chromatography -Mass Spectrometry (GC-MS) have been used to identify the potential causes of this effect. It shows that a small quantity of organic contamination deposited on silica surface is responsible for this degradation. Various hypotheses are proposed to explain the damage mechanism. The more likely hypothesis is a coupling between surface defects of optics and organic contaminants.

Profile of Maxicare Health Plan, Inc.

Since its conversion to a for-profit company in 1981, Maxicare has become a leader in the alternate health care delivery systems currently emerging in the United States. It has fostered a private practice physician network to provide care on a national scale to over 800,000 members and is currently entering the large New York City market.