[Cymraeg]

Optical Properties of Polymer Opal Thin-films

(supervisor: Chris Finlayson)

Nature of project: experimental, software

Available to full-time physicists or joint students.

Project description and methodology

All the laws of optics that you know are based on the assumption that optical media are fairly uniform. These laws break down completely when we make materials which are structured on the sub-micron size-scale of the wavelength of light often called photonic crystals.[1] New effects are then possible such as photonic bandgaps, super-prisms, slow light, and optical switching. Most photonic crystals are made using extremely expensive fabrication equipment and cover areas less than 1mm2. However, we use a new process for making photonic crystals which depends on the self-assembly of sub-micron sized plastic spheres, and allows us to make sheets of polymer opals which are metres long.[2]

In this project, the student will study the optical properties of pre-prepared thin-films of polymer opals, in which the resonant wavelengths of the structures coincide with visible wavelengths.[3] Iridescence is produced which comes only from the structural order rather than absorption by a dye; this is known as structural colour and has a number of important analogues in nature.[4]

A successful project will develop beyond the above in one/some of the following directions:
Measurement of complete 2D/3D "scattering cones" as a function of incident and reflection angles. Development of simple coding routines to handle data sets of multiple spectra.

When considering where to take your project, please bear in mind the time available. It is preferable to do fewer things well than to try many and not get conclusive results on any of them. However, sometimes it is useful to have a couple of strands of investigation in parallel to work on in case delays occur.

Additional scope or challenge if taken as a Year-4 project: There are many ways in which the project may be extended for a 4th year student. For example, a more detailed exploration of the dependence of light scattering on polarization, and of the anisotropic optical properties of polymer opals.

Initial literature for students:

  1. http://en.wikipedia.org/wiki/Photonic_crystal
  2. O. L. J. Pursiainen et al., Optics Express, vol.15, p9553 9561 (2007)
  3. C. E. Finlayson et al., Adv. Mater., vol. 23, p1540 1544 (2011)
  4. P. Vukusic and J. R. Sambles, Nature, vol. 424, p852 855 (2003)

Novelty, degree of difficulty and amount of assistance required

Students will need to be trained on a number of pieces of lab equipment relating to spectroscopic techniques. Appropriate assistance and training will be given.

Project milestones and deliverables (including timescale)

milestoneto be completed by
Equipment familiarisationChristmas
Experimental phasemid-March
Collation and data processingmid-March
Analysis/results completeEaster

Students taking this project will have to submit a full risk assessment form