Laser drilling system utilizing photoacoustic feedback

A system for drilling a workpiece having at least a substrate and a first layer on the surface of said substrate, comprising

• a controllable radiant energy source for directing a beam of radiant energy at a site on said first layer of said workpiece having a first photoacoustic signature, said source having a controllable input for varying its energy level as a function of a control signal received thereby;
• means for sensing a photoacoustic signal generated photoacoustically when said beam of radiant energy is incident upon said site on said substrate, said means for sensing producing an output in response to photoacoustic signals received thereby;
• control system means for controlling said radiant energy source including controller means having an input connected to said output of said means for sensing,
• said controller means having an output connected to the controllable input of said radiant energy source for supplying said control signal thereto, and
• data memory means for containing standard photoacoustic signature signals associated with a number of different materials adapted for comparison with photoacoustic signature signals of materials to be identified, said signature signals from materials to be identified being received from said means for sensing;
• said controller means comparing said photoacoustic signature signals from said sensor and said photoacoustic signature signals from said memory means for identifying the predetermined energy level to be employed by said source of energy for a given signature and thereby sending a predetermined signal to said radiant energy source to produce said energy level from said source.