A study on the incubation effect during multi-shot fs laser ablation of quartz

In the last two decades quartz has become a relevant material for sensing technology since it has been used for realization of various devices, such as Quartz Crystal Microbalance (QCM) or Quartz-Tuning-Fork (QTF). Micromachining of quartz can be realized through various techniques, such as diamond cutting, lithography, wet and dry etching, ion beam etching and Ultra-Short-Pulsed-Laser (USPL) processing. At the state-of-the-art USPL has been efficiently applied to quartz micromachining, e.g., for drilling and stealth dicing. In this study, the influence of the incubation effect and the repetition rate on USPL ablation threshold of quartz was systematically investigated. The multi-pulse ablation threshold of quartz was evaluated using 200 fs laser pulses at a wavelength of 1030 nm, at three different repetition rates, i.e., 0.06, 6, 60 and 200 kHz. Results show a strong decrease in the multi-pulse ablation threshold with the number of pulses N, as a consequence of the effect of incubation during the fs-laser ablation. Conversely, the influence of the repetition rate on incubation is negligible in the investigated frequency range. A saturation of the threshold fluence value occurs at number of pulses N > 100 and this trend is well fitted by an exponential incubation model. Using such a model, the single-pulse ablation threshold value and the incubation coefficient for quartz have been estimated. This investigation represents a first step towards the micro- and nano-texturing of quartz crystal for tailoring its mechanical, electrical, and optical properties.