TREATMENT OF METAL-SURFACES WITH EXCIMER-LASER RADIATION FOR RADIATIVE APPLICATIONS

In this study the effects of intense excimer laser irradiation (10(8)-10(9) W cm(-2)) on some radiative properties of copper, aluminum, magnesium, tantalum, and molybdenum are investigated. The short pulse duration of the excimer laser (30 ns FWHM) and the wavelength of the radiation initiate a processing regime that is dominated by the effects of a laser-supported plasma above the workpiece surface. A laser-supported detonation wave is observed that acts on a thin molten surface layer. The resultant structure that is frozen on the surface is dependent on the thermophysical properties of the metal and the number and manner in which multiple pulses are applied to the surface. This surface roughness has features on both the macro- and microscopic scale that affect the radiative properties of the surface. The surface plasma also initiates very fast reaction rates that can create a thick oxidized layer on the metal surface. The surface oxide layer may either be lightly (CuO particles on a copper substrate) or tightly adhered (Al2O3 on aluminum) to the surface. The effect of excimer laser irradiation is characterized with scanning electron microscopy and Fourier transform infrared spectroscopy. Data on solar absorptivity alpha(s), spectral reflectivity rho'(lambda), bidirectional reflectivity rho''(lambda), and total near-normal total emissivity epsilon'(T) are also presented that show that in some cases heavily irradiated samples simulate the radiative behavior of a flat absorber.