We have also worked with Prof Angus Silver at UCL to explore the advances that can be made in deep brain imaging using adaptive optics (Ref 8) and in separate work looked at methods of speeding up the AO process by using only a limited number of mirror shapes calibrated to specific depths within the sample (Ref 9, 10) This optical distortion is similar to that encountered by ground based astronomical telescopes where the distortion is caused by the atmosphere and is demonstrated by the images of cream cheese with increasing depth. As one images more deeply into the sample, however, the optics of the tissue distort the in coming excitation beam leading to a rapid increase in the focused spot size with a subsequent loss of resolution and signal.
The localised fluorescence excitation sets both the fundamental optical limit on the resolution and also the size of the focal volume has a significant effect on the excitation rate. More recently the challenge has been to enable the technique to image more deeply within tissue samples whilst maintaining sub-micron resolution. Initially the focus of the work was on the development of practical femtosecond laser sources (see Ref 4,5) enabled by working closely with the laser team within the Institute of Photonics, Strathclyde University. The research undertaken in the Centre for Advanced Instrumentation is then rapidly transferred put to work in a wide range of projects through the Biophysical Sciences Institute, thus maintaining the close relationship with the end users of the technique. The team's research is aimed at fully understanding the process of multiphoton microscopy and then developing innovative and practical solutions to improve the technique (see Ref 1,2,3). The technique provides the life scientist with the ability to image live samples in three dimensions with minimal damage to the tissue. The practical implementation of multiphoton microscopy in the early 1990s has led to a revolution in live biological imaging with sub-cellular resolution.