THERMAL-ACTIVATION IN KRF LASER-ABLATION OF CUCL

248 nm excimer laser ablation of carefully prepared CuCl samples is re ported, and shown to occur by a predominantly thermal mechanism. Using a quartz-crystal microbalance (QCM) to monitor ablation, a precise an d detailed plot of single-pulse mass removal versus incident fluence w as obtained for fluences up to 150 mJ/cm2. A two-parameter Arrhenius e xponential function was found to fit the experimental ablation data. C alculations of laser-induced surface heating were carried out by use o f a finite-difference heating code, formulated in terms of enthalpy. A blation was observed to commence at a fluence of 25 mJ/cm2, where the calculated surface temperature is approximately 910 K-some 200 K above the melting point. Dynamic ablation was included in the finite-differ ence calculation by allowing the position of the CuCl surface xi to va ry in time. The best data fit is provided by the zeroth-order kinetic equation: dxi(t)/dt=(16 angstrom/ns)exp[(-38 kJ/mole)/RT(xi)], where T (xi) is the surface temperature. A thermodynamic calculation shows the average heat of CuCl vaporization in the temperature range from 900 t o 2000 K to be near the fit value of 38 kJ/mole. From plots of the abl ation depth versus time, the CuCl surface was estimated to recede duri ng the ablation at rates up to 10 cm/s.