Advancing creation of micro-sized structures on surfaces

Dr Walter Perrie, PhD student Yang Jin and Dr Olivier Allegre at Lairdside Laser Engineering Centre

A “significant advance” in the creation of micro-sized structures on surfaces has been developed by University of Liverpool scientists working at Lairdside Laser Engineering Centre (LLEC).

For the first time, complex real-time surface patterning with dimensions approximately 1/200^th of the width of human hair was demonstrated. The patterning was enabled by dynamical switching between four polarisation states created from a high power, picosecond laser.

Two of the states had orthogonal, or intersecting, linear polarisations but the other two states, called radial and azimuthal, with spatially varying electric fields, unknown in nature, generated spatially varying surface features. When focussed on fixed spots, one formed a radial pattern and the other an azimuthal pattern consisting of concentric, circular rings with a period of ~ 0.5micron. Scanning the 4 states on a surface when modulated in real-time resulted in complex surface patterns which diffract white light into its spectrum very effectively.

Polarisations were switched at more than ten times per second, demonstrating a remarkable level of control.

The research was carried out by PhD student, Yang Jin and directed by Dr Walter Perrie and Dr Olivier Allegre, under the co-supervision of Dr Geoff Dearden and Dr Stuart Edwardson, in the School of Engineering’s Laser Group.

Chessboard pattern created with two linear polarisation states (left) and four linear polarisation states (right) viewed under white light, with the direction of illumination shown by red arrows

The team were also able to create a chess board type patterns by modulating two polarisations in real time, as well as creating the letters ‘LLEC’ on polished stainless steel utilising the four state real time surface micro-structuring technique developed.

Head of Laser Group, Dr Geoff Dearden said: “This is a significant advance in surface materials micro-structuring and the technique may have important future applications, including the improved performance of electrodes, complex security marking, the creation of photonic components and in the area of polarisation dependent spectroscopies. Efforts to increase the effective polarisation switching bandwidth are now in progress.

The research was published in Optics Express, Y.Jin et al, vol.21, No.21 (Oct 2013)