Digital micromirror devices and femtosecond laser pulses for rapid laser micromachining

Abstract

Laser machining techniques are almost ubiquitous in industry for micro- to nanoscale fabrication. It is essential for the advancement of the field that faster, cheaper processes be developed. Enhancements in speed and fidelity of production can be made to both additive and subtractive writing techniques by using Digital Micromirror Devices (DMD), particularly when coupled with femtosecond laser pulses. The objective of this thesis is the demonstration of DMDs used in conjunction with ultrafast laser pulses for both novel and rapid machining applications; primarily image-projection based techniques, using DMDs as dynamic intensity masks, will be used for subtractive patterning, laserinduced transfer, multi-photon polymerisation and centimetre-scale micro-machining. The dynamic nature of the DMD enables its application to the field of multiple exposures, and the centimetre-scale machining is applied to functional biological assays. Adaptive mask techniques are used to enhance the image reproduction achieved, correct for positional errors introduced by translation stages, as well as to attain greyscale intensity control with a DMD in single ultrashort pulses. A new technique for producing digital holograms is developed, and will form the basis of future work.

Image projection-based patterning using DMDs as dynamic intensity masks is shown via ablation, multiphoton polymerisation and Laser-Induced Transfer (LIT). Ablation was achieved in a range of materials (including, but not limited to: gold, graphite, diamond, bismuth telluride and antimony telluride, glass, nickel, glucose, and gelatin), with 2 micron resolutions in samples and overall sizes of 1cm2. A multiple exposure technique reduced final structure resolution by 2.7 compared to the diffraction limit possible in a single exposure – from 1m to 370nm on one experimental setup, and from 727nm to 270nm on a second setup. The first demonstration of shaped, solid-phase LIT deposits has been made, both in forward and backward directions of transfer.

Adaptive optics techniques have been developed for DMD mask corrections, and have reduced the positional error of samples introduced by translation stages. Greyscale intensity patterns have been projected at samples using the strictly binary-style DMD display technology, and the loss of intensity in high spatial frequencies at the sample has been addressed. A novel method for the generation of binary holograms is introduced, which allows for several additional degrees of control over spatial intensity patterns when using DMDs, such as the effective mask position relative to imaging optics, greyscale control, the formation of images at multiple planes, phase control, and overall lateral shifts of the intensity distribution below a single DMD pixel width.

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Identifiers

ORCID for Robert Eason: orcid.org/0000-0001-9704-2204

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