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Title: Dynamic polarization control using spatial light modulators for advanced ultrafast laser surface-structuring
Author: Jin, Yang
ISNI:       0000 0004 6422 8418
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2017
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Reflective liquid-crystal-based Spatial Light Modulators (SLM), addressed with optimised Computer Generated Holograms (CGH), have been integrated with two picosecond laser systems to control and manipulate the phase front and polarization states of laser beams, both statically and dynamically, for ultrafast laser surface microstructuring. Firstly, two SLMs were used in combination to structure the optical fields and wavefront of a 532 nm, 10-picosecond laser beam, producing planar or vortex wavefronts with radial or azimuthal polarization states. Multiple first-order cylindrical vector beams with vortex or planar wavefront have been generated and used to nano-structure a highly polished stainless steel metal surface. Then, synchronization of the two SLMs with the picosecond laser system was achieved for dynamic modulation of the polarization states of the laser beam. Consequently, for the first time, four states of polarization, linear horizontal and vertical, radial and azimuthal, all with a ring intensity distribution, were dynamically switched at a frequency up to ν = 12.5 Hz while synchronized with a motion control system and the 532 nm picosecond laser. Surface patterning with these 4 states resulted in ~ 0.5 μm pitch plasmonic structures, easily discernible when using white light diffraction. In separate experiments, CGH's applied to a single SLM were synchronised with a galvo scanner and a 1064 nm, 10 ps laser system for dynamic linear polarisation modulation. This real time polarisation control allowed complex laser surface patterning of polished metals with linear, periodic, ~ 1 μm pitch surface plasmonic structures. Hence, iridescent metal surface colouring with various geometric patterns was achieved. Finally, with an advanced digital scanner fully synchronized with the 532 nm, 10 ps laser system, high speed parallel multi-beam surface patterning of a 30 nm thick Aluminium thin film on a flexible Polyethylene Terephthalate (PET) was achieved. With laser repetition rate of 200 kHz and 8 diffracted first order beams, a film removal rate of R > 0.5 cm2/s was demonstrated with 5W average laser power delivered without damage to the PET substrate. The effective laser repetition rate was f ~ 1.3 MHz. During this work, the single pulse front and rear side single pulse ablation thresholds of the Al film on PET were determined to be Fth= 0.20±0.01 and 0.15±0.01 respectively, much lower than the PET ablation threshold, Fth=1.2, providing a clear processing window.
Supervisor: Dearden, G. ; Edwardson, S. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral