CN TEMPERATURES ABOVE LASER ABLATED POLYIMIDE

Polyimide is readily ablated by UV excimer lasers pulses. There exists an ongoing effort to determine the temperature (T) of the surface during the ablation process. The present experiment evaluates the temperature by means of high resolution laser-induced fluorescence measurements near the bandhead of the CN radical. The rotational state occupation indicates T = 1710 +/- 140 K for ArF (193 nm) ablation with 100 to 500 mJ/cm2. This temperature is near the extrapolation of earlier results at lower fluences (less-than-or-equal 80 mJ/cm2). Furthermore, modeling predicts T values essentially equal to the present experimental result when the following are included: thermal diffusion in the solid, above surface UV absorption and increasing specific heat for temperatures above ambient. The present T-value reinforces the concept that thermal energy probably promotes the intermediate steps in photoablation.