A new approach for 4D spatial-spectral optical sensing is based on light diffraction at holographically recorded 3D
refractive index gratings. At least four collimated laser beams overlapped in a photosensitive polymer layer are used to
generate a periodic 3D structure. Diffraction properties are widely adjustable by varying the recording beam geometry.
Different 3D photonic gratings are characterized with respect to their basic diffraction properties and the results are used
in optimizing the exposure process and parameters. An optical imaging setup has been constructed to display the 4D
optical filtering properties of recorded 3D gratings when illuminated by elementary intensity patterns of a white light
source.
Diffractive optical elements with application specific tailored properties can be fabricated by light induced alternation of
the material's refractive index. Holographic polymers or photoresists are typically used for permanent optical
structurization. Today, photostructurable media become core elements of photonic systems with innovative capabilities.
We investigate different classes of organic photosensitive materials in order to optimize the interaction between the
material and an optoelectronic system around. Some exemplary applications are microholographic data storage, 3D
nano/micro structurization, optical patterning for advanced security features. Key issues include dynamic material
response, spectral and temporal grating development, influence of the light intensity distribution, effects of pre-exposure
and post-curing, etc. Materials under investigation are cationic and free radical polymerization systems, liquid crystalline
polymer nanocomposites, and photoresist systems.
3D holographic gratings with variable periodicity represent a central part of an optical sensing system. Periodic spatial
modulation of the refractive index in all three dimensions is holographically induced by multiple beam interference. The
periodicity of the resulting volume diffractive optical structure is controlled by the recording beam geometry. The
recording medium is a photosensitive polymer. An experimental setup for creating and analyzing such 3D gratings is
presented as well as first results achieved in a 300 μm thick photopolymer sample.
A novel approach to 3D optical information storage based on writing and reading of microscopic holographic gratings in a photopolymer layer is presented. Strongly localized reflection gratings created by two highly focused laser beams are used to replace the pit and land structure of the CD/DVD technology. The holographic recording method presented here allows employing various multiplexing methods. A combination of wavelength multiplexing and multilayer storage is
proposed to achieve storage densities similar to page-oriented holographic data storage. In this paper we report on recording and readout of submicron-sized gratings using diffraction limited laser beams. The transversal extent of a micrograting corresponds to the optical resolution limit. Track spacing and bit-to-bit separation are about 500 nm. The interlayer spacing through the depth of the photopolymer is less than 8 micron. This way a 3D structure is realized that even refines the surface data structure of current DVDs.
We present a new technique for high-resolution colocalization of fluorescent dyes. The technique is based on polarization modulated excitation and spectrally-resolved fluorescence lifetime imaging microscopy (SFLIM) as well as on coincidence analysis of the detected photon counts following pulsed laser excitation. The method takes advantage of single fluorescent dyes that can be efficiently excited by a single pulsed diode laser emitting at 635 nm but differ in their emission maxima, and in their fluorescence lifetime. A combined analysis of the fractional intensities and fluorescence lifetimes recorded on two spectrally-separated detectors enables the classification of the portion of each dye per pixel in a point-spread-function (PSF) image with high accuracy, even though only a limited number (generally a few thousand) photons are detected per single dye. From these portions two separate PSF images are calculated and fitted to two-dimensional (2D) Gaussian functions to localize their centers with a precision of a few nanometers. To reveal the number of absorbing and emitting molecules polarization modulated excitation and coincidence analysis of the detected photon counts is used. We demonstrate that by the use of appropriately selected dyes, the presented technique permits (1) the counting of the number of molecules present in the observation volume, and (2) the determination of the distance between two single molecules down to approximately 30 nm with a precision of approximately 10 nm without any chromatic aberrations. The developed techniques are promising for applications in molecular biology, e.g. to determine the number of polymerase molecules active within a transcription factory and/or to measure their distances to nanscent transcripts.
An optical system for writing and reading of microscopic holographic gratings in a photopolymer layer is presented. The reflection gratings created by a highly focused laser beam can be used to replace the pit-land structure in a disk-based optical storage system. The modulation range of such three-dimensional microgratings is clearly localized to the focal region of a focused write beam. Holographic recording allows for using various multiplexing methods. To achieve storage densities higher than currently available, we propose a combination of wavelength multiplexing and multilayer storage. The fist steps in the system development as well as microholographic recording in Aprilis CROP photopolymers are reported.
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