Optics group research overview

Editor's Notes

1. Generates spatially varying polarisation patterns from uniform input light in a broadband manner due to total internal reflection (phase shift between the s and p polarisation components at the cone surface; the definition of s and p varies azimuthally) Output beam carries OAM Can be used to generate radial or azimuthal polarisation Can be used as a polarimeter for uniform polarisation
2. Vector beams, generated from cones, DMDs/SLMs, or q-plates as shown here, in conjunction with carefully controlled magnetic fields can lead to phase-dependent absorption in cold atoms In this scenario atoms are transparent for one linear polarisation – similar to polariser, direction of which is dictated by the direction of external magnetic field: can be used to measure small magnetic field deflections Atoms also give rise to potentially massive dispersion due to Kramers-Kronig relations, leading to slow light – potential to use as a spatially dependent quantum memory
3. Potential use in low vision aids for people with impaired vision. Top is two sheets of lenslets, placed confocally (i.e. a telescope). Bottom is an array of dove prisms (a) and a confocal lenslet array (b). Here (b) is the same as (c) above. Two sheets of (b), suitably placed, rotate the view. Right, is this in action with (cheapish) lenslets.
4. The end goal of Kevin’s broadband beam shaper is to have arbitrary spatial control and polarisation control of either white light or ultrashort pulses of light. This is a similar goal to Neal’s achromatic vortex beam with the glass cone, except I can theoretically generate any polarisation, not just the shapes dictated by the cone shape.
5. There is interest in the use of spatial optical modes for encoding both quantum and classical information. At the most fundamental level, a photon has many degrees of freedom: polarisation, frequency, position, spatial mode, etc., any of which can be used to encode information but all create additional channels. However at the quantum regime, the extent to which one can encode information simultaneously and independently in both the position and momentum variables is limited by the uncertainty principle, which applies also for angular position and angular momentum.
6. A commonly used source of entanglement is a pumped beta-barium-borate (BBO) crystal. One technique to generate spatially entangled light and that was used in this experiment relies on pumping a non linear beta barium borate, or BB0, crystal with 355nm UV light. Approximately one in a billion of these photons will split into two photons at around 710 nm wavelength, due to energy conservation. In the image plane we observe correlations in the positions of the photons and in the far-field we will find anti-correlations in their measured momenta. The error in the locations of the photons in the imaging plane is defined by the length of the crystal and the wavelength of the degenerate light. The sum of the positions in the far-field will be centred around zero, with an error defined by the size of the pump beam.
7. Recent years have seen a rapid advance in imaging technologies. Developments in low-noise electron multiplying CCD (EMCCD) cameras suggest they are capable of ~ 90% QE and can provide single photon sensitivity.