Dr Dave Phillips

I joined the department of Physics and Astronomy at the University of Exeter in June 2017 and established the 'Structured Light Group'. We are a team of 4 PhDs students and 2 postdoctoral researchers working on a range of projects spanning experimental optics and photonics, linked by their reliance on 'structured light' - precise shaping of the intensity, phase and polarisation (and also sometimes wavelength) of laser beams. Structured light fields find applications across many different areas of research. In particular, we use structured light to manipulate small particles in a microscope (optical tweezers), and to develop new types of imaging systems with capabilities beyond those of conventional cameras.

Read on for more information about our work, and see here for our recent publications: https://scholar.google.co.uk/citations?hl=en&user=MOJZLlAAAAAJ&view_op=list_works&sortby=pubdate

Optical Tweezers - Light carries momentum, and this momentum can be used to exert forces on and manipulate microscale objects such as single cells. To understand how this is possible, imagine shining a torch on a glass football - the torchlight bends as it refracts through the glass interfaces. The light exiting the football travels in a different direction from that entering the football. Since the momentum of the light has changed, so must have the momentum of the football (by conservation of momentum). Therefore the light exerts a force on the football. We don't normally notice this because the force is vanishingly small. However, if we shrink the glass football down to the size of a cell (~10 micrometers, a tenth of the width of a strand of hair) and replace the torch with a powerful laser beam, this force does become noticeable - at this scale we can use light to manipulate particles in a microscope - a technique known as optical tweezers. We study how optical tweezers can be used to image and investigate the microscopic world, including biological systems, in new ways.

Computational Imaging - The way we take pictures is changing. Conventional imaging systems use lenses to form an image directly onto a camera sensor (or a piece of film). Computational imaging systems offload the task of image formation to a computer, allowing the reconstruction of images from measurements on a scene in a more abstract way - without ever physically forming an image. This concept has spawned a wide range of new kinds of imaging system, that make use of an understanding of how light fields evolve as they propagate, or that can reconstruct images using just a single pixel by loading spatial image information onto temporal or spectral degrees of freedom. We develop new computational imaging systems that can take pictures at wavelengths where conventional camera sensors don't exist.

Complex Photonics - When light propagates through an opaque material, such as living tissue, it fragments and scatters multiple times. Such a situation is known as a complex photonic environment. This scattering scrambles any spatial information the light carries, preventing the formation of images of objects behind (or inside) the scattering system. Only relatively recently has it been shown that although highly complex, this process is deterministic, and it is possible to use digital light shaping technology to measure and reverse the scattering. This capability promises a range of powerful new imaging systems capable of imaging in situations previously intractable. Examples include imaging inside the human body using non-ionising visible light, imaging through fog, and imaging around corners. Before these developments can be fully realised there are many remaining obstacles, and we work on overcoming these challenges using concepts from the field of computational imaging to build next generation imaging systems.

Wherever possible we like to use numerical modelling to accompany experiments in the lab. - the beauty of this area of physics is that often the real world and the simulated world agree surprisingly well!

If you would like to know more about the work of the Structured Light Group then please drop me an email.