Formation of embedded patterns in glasses using femtosecond irradiation

Channel formation in glasses is demonstrated and discussed. Photosensitive glass (Foturan) was microstructured using femtosecond irradiation at 800 nm and 400 nm wavelengths, with subsequent thermal annealing, and HF etching of a lithium-silicate phase formed by exposure-annealing. It was found that there is a significant difference in the volume of lithium-silicate when the exposure was made with and without optical breakdown. Channels with a minimum cross section of approximately 10 μm were achieved. In silicate glasses, the optically induced dielectric breakdown was used for the recording of channel patterns. The highest wet etching rate in a HF based solution was observed when the irradiance corresponded to the 2.5-3.0 thresholds of dielectric breakdown and the adjacent pulses were overlapping by more than 50% of the diameter of the focussed beam. Under these conditions, the formation of void inside the glass was confirmed by optical observation of single shot damage under a microscope. The mechanism of selective wet etching in silicate glasses is discussed in terms of the stress corrosion effect, which explains crack propagation in glasses via the reaction of stretched Si-O-Si bonds at the tip of a crack with water, resulting in SiOH formation. It is shown that intra-connection of voxels was the key factor to achieve etching of high aspect ratio patterns in silica glass.