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The optical coherence tomography (OCT) is an important technology for non-invasive, in vivo medical diagnostics. It enables the high-resolution recording of two-dimensional tomograms or three-dimensional volumes of biological tissue. Two mechanisms help separating the signal from the scattering background. First, reflected or backscattered light from outside the focal spot is suppressed by confocal discrimination. Additionally, the signal modulation is enhanced due to identical optical path lengths of both branches of the white light interferometry setup. Since the OCT relies on the interference between reference light and scattered light, this method cannot be readily extended for fluorescence measurements.
An alternative approach is the confocal fluorescence microscopy, which uses confocal microscopy to suppress the fluorescent light from outside the focal spot. Hence, only the fluorescent light in the focal plane, which is 3 to 4 magnitudes lower in intensity than the excitation light, is detected. However, the surrounding area is illuminated with full intensity, which might cause photo-bleaching. There are also other promising approaches such as the two-photon excitation microscopy or fluorescence lifetime microscopy, which we will not cover in more detail.
For fluorescence measurements of strongly-scattering samples such as biological tissue but also for technical surfaces, we propose a structured white-light illumination. We present two different approaches for the sample illumination utilizing a white light laser or a white light LED, respectively. We show first simulations of the individual illumination setups and their impact on the scattering within the sample. Furthermore, we investigated the distribution of the fluorescent light that reaches the detection part of the device when excited within a scattering medium, for this purpose we implemented a novel fast-converging algorithm for conditional fluence rate in our Monte Carlo algorithm.
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