Determination of High-Temperature Properties Relevant to Laser Materials Processing

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ABSTRACT -- CTS-9312325 PI -- Michael F. Modest While laser processing (drilling, cutting, welding) is gaining industrial importance at an extremely rapid pace, the basic process remains poorly understood, largely because of a dearth of knowledge of high-temperature property data (of the material being processed, and of the laser plume forming above it). Sophisticated models exist that could accurately predict drilling rates, hole diameter, taper, cutting rates, etc., were it not for this lack of property data. This proposal addresses three groups of experiments, which will be carried out to measure all relevant high-temperature properties for CO2 and Nd:YAG laser processing of ceramics: (1) The absorptivity of several ceramic specimens (at the laser wavelengths, as a function of temperature), the ablation temperature, and the energy required to ablate material will be measured in an integrating sphere apparatus. (2) The laser interaction zone will be imaged through high-speed photography and infrared thermometry to capture the removal mechanism (ablation, decomposition, melting, or micro-explosive removal) and to identify debris removal and redeposition. (3) Absorption coefficients of the laser plume will be measured at the laser wavelengths (to determine amount of beam blockage) and in the mid-infrared (to determine re-emission from the plume) using transmission and emission spectroscopy. Results from this investigation will allow quantitative predictions for laser processing of ceramics, and will provide experimental designs to measure the relevant properties for other materials, including metals.