Holographic spatial Fourier-filtering in optical microscopy

We intend to investigate new methods in optical microscopy, which provide higher image contrast and/or a higher resolution than obtainable in standard microscopy, and which will allow quantitative imaging and interferometry of microscopic samples in biology and material research. The methods are based on the features of recently available spatial light modulators (SLMs), which are miniature liquid crystal screens with an extremely high resolution on the order of 1 million pixels per cm. These screens can act as programmable amplitude-, phase- or polarization- modulators for the image beam, with a resolution which is sufficiently high to display computer generated holograms. These SLMs are introduced in the optical beam path, and perform different tasks of so-called spatial filtering, or interferometric superposition of the image beams. Furthermore, these spatial filters can be used for both, controlling the illumination beam and performing a "matched" spatial filtering of the image field. For example, a beam with an amplitude or phase modulation controlled by a first SLM can be projected at the sample for illumination, and the transmitted (or reflected) image beam can be guided through a second SLM in order to extract additional information from the image field, which is not available with standard methods. In previous experiments we have already demonstrated the advantageous features of a particular type of spatial filter - a so- called "doughnut" or spiral phase filter - to produce strong edge enhancement of shallow phase samples. The same method also enables a new kind interferometry which allows object reconstruction from one single "spiral fringe interferogram". In the present project we intend to expand our research to new types of spatial filtering, and to matched illumination and image field filters, which can be programmed to highlight selected object features. In more detail, we plan to build a prototype microscope with high quality components including a structured illumination facility with a first SLM, and a spatial Fourier filtering facility with a second SLM, to surpass professional research microscopes in imaging contrast and resolution. With this system we will develop and evaluate new types of holographic spatial Fourier filters (e.g. spiral phase filters with higher helical indices) , which are matched to highlight selected features of a sample object, like amplitude or phase gradients, or the curvature of a sample`s phase topography. We also intend to apply the flexibility of the SLM-setup to develop new interferometric methods for quantitative imaging of sample details on a sub-wavelength scale. We expect that the results of the proposed project may boost the performance of optical microscopes. The experiences obtained with the flexibly programmable SLMs in the imaging system can be used to manufacture "hardware" components like phase plates with optimized properties, which promise to achieve the demonstrated effects with an even better performance, and at low cost. Therefore the results of our research may have a considerable impact on optical microscopy, and also advance research fields where microscopy is applied, like material research or biological sciences.

We intend to investigate new methods in optical microscopy, which provide higher image contrast and/or a higher resolution than obtainable in standard microscopy, and which will allow quantitative imaging and interferometry of microscopic samples in biology and material research. The methods are based on the features of recently available spatial light modulators (SLMs), which are miniature liquid crystal screens with an extremely high resolution on the order of 1 million pixels per cm. These screens can act as programmable amplitude-, phase- or polarization- modulators for the image beam, with a resolution which is sufficiently high to display computer generated holograms. These SLMs are introduced in the optical beam path, and perform different tasks of so-called spatial filtering, or interferometric superposition of the image beams. Furthermore, these spatial filters can be used for both, controlling the illumination beam and performing a "matched" spatial filtering of the image field. For example, a beam with an amplitude or phase modulation controlled by a first SLM can be projected at the sample for illumination, and the transmitted (or reflected) image beam can be guided through a second SLM in order to extract additional information from the image field, which is not available with standard methods. In previous experiments we have already demonstrated the advantageous features of a particular type of spatial filter - a so- called "doughnut" or spiral phase filter - to produce strong edge enhancement of shallow phase samples. The same method also enables a new kind interferometry which allows object reconstruction from one single "spiral fringe interferogram". In the present project we intend to expand our research to new types of spatial filtering, and to matched illumination and image field filters, which can be programmed to highlight selected object features. In more detail, we plan to build a prototype microscope with high quality components including a structured illumination facility with a first SLM, and a spatial Fourier filtering facility with a second SLM, to surpass professional research microscopes in imaging contrast and resolution. With this system we will develop and evaluate new types of holographic spatial Fourier filters (e.g. spiral phase filters with higher helical indices) , which are matched to highlight selected features of a sample object, like amplitude or phase gradients, or the curvature of a sample`s phase topography. We also intend to apply the flexibility of the SLM-setup to develop new interferometric methods for quantitative imaging of sample details on a sub-wavelength scale. We expect that the results of the proposed project may boost the performance of optical microscopes. The experiences obtained with the flexibly programmable SLMs in the imaging system can be used to manufacture "hardware" components like phase plates with optimized properties, which promise to achieve the demonstrated effects with an even better performance, and at low cost. Therefore the results of our research may have a considerable impact on optical microscopy, and also advance research fields where microscopy is applied, like material research or biological sciences.