| dc.description.abstract | This study aims to develop a two-step laser irradiation method for precise machining on thin glass substrate using a picosecond pulsed laser micromachining system. This system is able to switch the picosecond laser to deliver one of the three wavelengths of 1064, 512, or 355 nm. The target substrate is thin alkali-free glass. The first step irradiation is for glass modification that involves irradiating the substrate with the picosecond pulsed beam operating at the wavelength of 1064 nm. The absorbed incident laser energy increases the local temperature of the glass and modifies its light absorptivity, not only for the wavelength of 1064 nm but also for other wavelengths of light. The second step is the precision laser machining, which is accomplished by irradiating the modified area with 355 nm ultraviolet light. Since the absorptivity of the alkali-free glass against UV laser is enhanced after the modification step, the threshold of laser machining on alkali-free glass would be decreased. Hence, the minimum power required for UV laser machining on the modified glass is reduced, thereby making processing easier. In this study, the influence of the three processing parameters, energy per pulse, pulse repetition rate and irradiation time on the machining quality is considered. Results show that a modified area was able to be generated under the processing parameters of energy per pulse of 60 μJ, pulse repetition rates of 2.5, 5, and 10 kHz, respectively. The irradiation time, however, is not that significant. In the step of UV laser machining, by using the same processing parameters on the modified and unmodified areas, the former can be processed, while the later has no effect. The same result can be obtained regardless of whether the machining is processed by single point irradiation or by line scanning. Finally, the absorption measurements on the modified and the unmodified non-alkali glass were conducted. It is found that the modified alkali-free glass has a slight increase in the absorption of the 355 nm wavelength. In summary, this study demonstrates the feasibility of the proposed scheme in laser glass micromachining. | en_US |