MECHANISM OF TOPOGRAPHY FORMATION DURING CO2-LASER TEXTURING OF SILICATE-GLASSES

A theoretical picture is advanced to explain experimental results of C O2 laser texturing of silicate glasses. Common characteristics among s everal glass types are found that corroborate observations made by oth er investigators and establish features of glass laser texture. The pr incipal experimental results include increasing bump height with pulse energy (above some threshold); bump width scales with the bump height ; annealing, before or after laser texture, reduces bump heights; and finally, further growth in bump height occurs with a finite number of laser pulses subsequent to the first. Explanations for these results h ave been unified in terms of a ''fictive temperature map'' that relate s microstructure to the thermal history of the glass. On this map, the glass transition temperature identifies a fictive temperature at whic h the rate of change of temperature is comparable to the rate of chang e of the microstructure. Therefore, the time scale imposed by the lase r pulse can elevate the transition temperature of the glass, making ac cessible high fictive temperatures to the heat affected zone. As a res ult of this description we can offer explanations to important charact eristics of glass laser texturing, perhaps most notably the nonlinear threshold dependence of bump height on pulse energy. We can also expla in the observed bump growth with multiple laser pulses, the effect of chemical strengthening, and the effect of annealing before or after la ser texturing. (C) 1998 American Institute of Physics. [S0021-8979(98) 05317-1].