Ultrafast laser micromachining the ultra-low expansion glass-ceramic: Optimization of processing parameters and physical mechanism

To fulfill the precise requirements of laser gyroscope for inertial navigation, using the mean surface roughness, taper angle and circularity degree as indicators, we optimize the processing parameters about ultrafast laser micromachining a commercial ultra-low expansion glass-ceramic (ULGC). Furthermore, through careful characterizations, we identify the sequential appearance of photo-darkening, crystalizing, melting, foaming and vaporizing regions during the interactions of ultrafast laser with ULGC. Especially, the foaming region is identified to effectively mediate the thermal stress at the interfaces between different regions. Originated from the Gaussian distribution of energy, poor processing quality by a Gaussian beam is mainly ascribed to the formation of various regions. By using a Bessel beam, higher surface quality could be obtained due to the possibility of the occurrence of only a foaming region in irradiated regions. This discovery gives us an important clue to optimize processing parameters to obtain high-quality ultrafast laser micromachining surface.