Laser–material interaction and grooving performance in ultrafast laser ablation of crystalline germanium under ambient conditions

Abstract

Microgrooving on crystalline germanium (Ge) <100> surface using 1064 nm wavelength ultrafast laser pulses under ambient condition is investigated. The interaction of laser and target material and the influence of processing parameters such as laser power, pulse repetition rate and scan speed on the groove dimensions and surface roughness are studied. For the laser radiation fluence range used (0.4–0.8 J/cm2), material removal is primarily controlled by optical penetration depth. The depth and width of grooves increase with laser power. In multipulse irradiation, heat accumulation due to residual thermal energy from successive laser pulses results in a greater material removal. Furthermore, groove depth and width decrease as the pulse repetition rate increases from 0.5 to 2 MHz, due to the decrease in pulse energy with an increase in repetition rate causing ablation threshold fluence to move towards the central portion of the Gaussian pulse. Surface roughness has not shown significant changes for the parameters used in this study. A micro-Raman analysis of groove surfaces reveals a change in the crystallinity of the Ge due to laser irradiation.