Product Code: ICA12_M309

The Impact of Graphite Coating and Wavelength on Laser Machining of Optical Glasses - Invited Presentation - 40 Minutes
Authors:
Krystian L. Wlodarczyk, Institute of Photonics and Quantum Sciences, School of Engineering and Physical Sciences, Heriot-Watt Univ.; Edinburgh Scotland
Frank Albri, Institute of Photonics and Quantum Sciences, School of Engineering and Physical Sciences, Heriot-Watt Univ.; Edinburgh Scotland
Robert R. J. Maier, Institute of Photonics and Quantum Sciences, School of Engineering and Physical Sciences, Heriot-Watt Univ.; Edinburgh Scotland
Nick J. Weston, Renishaw Plc; Edinburgh Scotland
Duncan P. Hand, Institute of Photonics and Quantum Sciences, School of Engineering and Physical Sciences, Heriot-Watt Univ.; Edinburgh Scotland
Presented at ICALEO 2012

Optical glasses are used as substrates of refractive and diffractive micro-optical components. Although many mechanical and lithographic techniques have been developed to fabricate these components, lasers are also useful for manufacturing of micro-optics, especially for custom parts or low volumes, where process flexibility is important. The relatively high absorption of optical glasses at the 10.6 "m wavelength suggests that a CO2 laser is the ideal tool for fabrication of free-form micro-optical components. However, the relatively long wavelength means that the laser spot size is limited to tens of microns, which means that it cannot generate surface features which are smaller than 20-30 "m. Moreover, the heat generated by CO2 laser irradiation means that only glasses with a low thermal expansion coefficient, such as fused silica, can be successfully machined without fractures. A good alternative is to use ultrafast laser pulses, and in this paper we present a picosecond laser machining process for optical glasses, such as fused silica and Borofloat"33, providing micron resolution and an excellent control over the laser-machined area. In this process a graphite layer was deposited onto the glass surface before laser treatment in order to achieve better absorption at wavelengths where the glasses are normally transparent. The ablation threshold, volume removal rate, ablation efficiency, machining precision together with achievable feature sizes and aspect ratios were determined for three different wavelengths (» = 343, 515, 1030 nm) and compared with the results obtained without the graphite layer. The advantages, limitations and potential applications of this process are presented.