Digital micromirror devices for laser-based manufacturing on the micro-scale

Digital micromirror devices (DMD), such as the DLP range developed by Texas Instruments, have found many applications in scientific research. Here, we show how a DMD can be used as a spatial light modulator for an 800nm wavelength, femtosecond laser system, to enable image-projection-based laser machining, for both additive and subtractive manufacturing. Laser pulses incident on the DMD were spatially shaped by the DMD pattern and demagnified, via a microscope objective, to a size of ~30µm by 30µm onto a target sample, hence providing a ~1000 increase in laser fluence compared to that on the DMD surface. Typically 1-10J/cm2 was achieved on the target sample, which enabled ablative patterning of a range of materials ranging from thin-film semiconductors to bulk diamond. As only a single laser pulse was required to machine an entire pattern, through the use of automated stages, stitched cm2-sized regions, with diffraction-limited resolution, were machined on a time scale of minutes. The ability to synchronise the DMD updating with the arrival time of the laser pulses enabled each laser pulse to be individually spatially shaped providing significant flexibility to machine arbitrary cm2 structures. We will present examples of both subtractive (laser-ablation) and additive (photo-polymerisation and laser-induced-forward-transfer) manufacturing, show how this approach can fabricate structures smaller than 1/10th of the laser wavelength, and demonstrate a technique that modifies a surface to produce complex multi-coloured patterns (achieved via the ablation of micron-sized variable-period-gratings) that may have applications in the security and marking industries.

Mills, B.

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Heath, D.J.

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Feinäugle, M.

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Eason, R.W.

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February 2015