Pulse to Pulse Control in Micromachining with Femtosecond Lasers.

Ultra-fast laser in micromachining have a reputation of highest precision and quality, which justifies additional invest in numerous applications. However, deficits in the synchronization of the positioning of beam deflection device and laser triggering -in particular at high repetition rates- still lead to defects like overtreatment due to the inertia of the mirrors of galvanometer scanners or path deviations at complex shapes. This in turn has led to an increasing demand of advanced pulse to pulse control for precise laser energy deposition. Two recent innovations have the potential to overcome these current limitations. Firstly, the scan ahead feature allows to calculate the actual beam position in acceleration and deceleration mode. According to the precise position feedback the control needs to adjust the repetition rate of the laser source e.g. at rectangular corners of a scan trajectory. Therefore, the pulse on demand feature at the laser interface is obligatory to dynamically adjust the pulse to pulse delay in order to accomplish constant energy deposition at any programmed scan pattern. We have put these two innovations to a test by combining an Excelliscan from Scanlab with an UV Tangor laser from Amplitude to validate the synchronization and constant pulse separation at various scan speeds and geometrical patterns. Applications trials like engraving with scan speed are presented in comparison to conventional scanning techniques to demonstrate the benefit of the fast synchronization and pulse on demand technologies.