Structured Illumination and Image Inversion Interferometry

An overview of recent advances in high resolution fluorescence microscopy will be given. In structured illumination the sample is illuminated with a number of different patterns of light. In our case this is a series of sinusoidal grids at different grid positions and orientations generated by a programmable spatial light modulator or a physical phase grating. Experimental datasets acquired under these conditions and reconstructed results from these data, demonstrating a resolution improvement of up to a factor of two over standard widefield microscopy are presented. The non-linear approach of saturating optical transitions (for structured illumination as well as beam-scanning approaches) has a great potential especially in combination with photo-switchable dyes such as the recently described IrisFP protein from Ulrich Nienhaus’group or the Cy3-Alexa647 system used in Xiaowei Zhuang's group. An interesting approach is to push molecules into dark states in a patterned way shortly before imaging and exploiting the saturation of this transition. Finally a method will be presented in which the emitted fluorescence of a confocal microscope passes through two separate paths. These paths are interferometrically recombined in such a way that the images undergo a mutual rotation of 180 degrees. The self-interference of the fluorescent light is only constructive, if it originated from the optical axis of the scanning laser beam, thus leading to an efficient detection of a high resolution fluorescence images. K. Wicker, S. Sindbert, R. Heintzmann, Characterisation of resolution enhancing image inversion interferometers, Optics Express 17, 15491-15501, 2009 L. Hirvonen, K. Wicker., O. Mandula and R. Heintzmann, Structured illumination microscopy of a living cell, Europ. Biophys. J. 38, 807-812, 2009