Abstract

The mechanism by which UV laser pulses bring about the etching of tissue surfaces with a minimum of thermal damage to the substrate has been a matter of controversy. There are two aspects to this problem which are: (i) the reaction path in which the chemical bonds are actually broken, and (ii) a quantitative model of etch behavior as a function of pulse width, wavelength, and fluence. The second aspect is addressed here. A model is proposed¹ which relates the time-dependent passage of the laser pulse to experimental parameters which control the etch behavior. A photochemical mechanism is assumed and the rate of decomposition of the polymer in its excited state is viewed as a process which competes with alternative processes which do not lead to decomposition. The width of the laser pulse is a critical factor because it is only the flux of absorbed photons above a threshold value that will be available for bond-breaking. The predictions made from this model regarding the relationship between the pulse width and fluence thresholds are being tested and have yielded encouraging results.

© 1986 Optical Society of America