Polarisation microscopy of single emitters

• Main Author: Clegg, James
• Other Authors: Neil, Mark
• Published: Imperial College London 2015
• Subjects: 530
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.682098

This thesis contains a report on the development of a new type of confocal microscope. The microscope aims to allow the user to be able to determine the three dimensional orientation of single fluorescent emitters. The microscope has at its heart a binary spatial light modulator that allows us to control the excitation electric field in the pupil of the microscope objective. This allows us to exploit the fact that the excitation of, and emission from, a single fluorescent emitter is polarisation and orientation dependent. By changing the field in the excitation pupil we can generate a set of images that when taken together can be analysed to find the emitter orientation. We show that the microscope allows us to resolve the orientation of single fluorescent molecules and nitrogen vacancy centres in nanodiamond. We designed the microscope from scratch using extensive mathematical modelling techniques. We anticipate that these models will be useful to other researchers. One example is that our model of the polarisation distortions introduced during scanning is relevant to any galvanometer-based scanning system. We also developed a full model of a confocal microscope that includes the dipole-like nature of many samples. We use this to calculate, amongst other things, the optical sectioning properties of confocal microscopes. This allows us to validate previous models that ignored polarisation distortions of high numerical aperture lenses and also to make calculations where previous models would have been inadequate, for example in calculating the sectioning strength of sheets of aligned dipoles. As well as developing numerical models, we invented a new method for controlling the polarisation of light using a binary spatial light modulator. This work has applications in materials science, and industrial applications.