Laser percussion drilling of transparent hard and brittle materials with ring-shaped electrodes

Abstract

This paper presents an innovative approach to detect plasma induced by laser drilling in a laser processing system using an external sensing electric field. The system uses a sensing electrode to detect the plasma signal, which is then sent to the controller in real-time via an embedded signal sampling rate system. The system is capable of accurately sensing the pulse repetition rate from 0 to 500 kHz during laser processing, with a signal sampling rate of up to 1 MHz. The controller analyzes the plasma signal and adjusts the laser focus position by controlling the servo motor to achieve real-time detection of laser drilling. The paper compares several configurations of electric field assistance, including parallel type interdigitated electrodes, mask type interdigitated electrodes, ring shape electrodes, and parallel type interdigitated electrodes without a steel plate. The electric field strength and power line distribution of the electric field were simulated using the COMSOL Multiphysics finite element software, and the system was tested on sapphire and quartz glass. The experimental results showed that in the presence of the electric field, the opening diameter decreased by 8 % and 12.13 %, respectively, for sapphire and quartz glass, compared to the case without the electric field. Moreover, the exit diameter increased by more than 100 % and 49.79 %, the ring shape taper angle decreased by 23.31 % and 33.74 %, the machining time decreased by 66.22 % and more than 40 %, and the opening heat affected zone decreased by 24.45 % and more than 50 %, for sapphire and quartz glass, respectively.