Opto-electronic position sensing method

A method for drilling a hole in a workpiece target capable of at least partially reflecting light in a scattered manner, wherein an incident laser beam of less than drilling intensity is directed along an incident beam axis onto the target through an incident beam focusing means, scattered light from the incident beam reflected from the target is collected from a position other than on the incident beam axis along a reflected light axis which intersects the incident beam axis at an axis intersection, the scattered light being focused on a photosensitive means which provides an output signal including a portion which is a function of displacement of the focused light from a reference of the photosensitive means representing the axis intersection, the improvement comprising the steps of:

• positioning the axis intersection and the target at a preselected position with respect to one another along the incident beam axis by first positioning the axis intersection on the target and then moving the axis intersection a preselected distance along the incident beam axis to adjust the size of the hole to be drilled in the target;
• and then
• directing a drilling laser beam of drilling intensity through the incident beam focusing means toward and into contact with the target along the incident beam axis for a time sufficient to remove desired material from the target.