ABSTRACT
A pair of combined diffractive optical elements (DOEs) realizes a so-called moiré lens, with an optical power which can be tuned by a mutual rotation of the two DOEs around their central optical axis. Earlier demonstrated moiré lenses still suffered from chromatic aberrations. Here we experimentally investigate a multi-color version of such a lens, realized by a pair of multi-order DOEs. These DOEs have a deeper surface structure which modulates the phase of the transmitted light wave by several multiples of 2π. The corresponding multi-order moiré lenses all have the same focal length at a fixed set of harmonic wavelengths within the white light spectrum. The experiments demonstrate that multi-order moiré lenses have significantly reduced chromatic aberrations. We investigate the performance of the lens for narrow band and white light imaging applications.
ABSTRACT
Alvarez lenses are actuated lens-pairs which allow one to tune the optical power by mechanical displacement of subelements. Here, we show that a recently realized modified Alvarez lens design which does not require mechanical actuation can be integrated into a confocal microscope. Instead of mechanically moving them, the sublenses are imaged onto each other in a 4f-configuration, where the lateral image shift leading to a change in optical power is created by a galvo-mirror. The avoidance of mechanical lens shifts leads to a large speed gain for axial (and hence also 3D) image scans compared to classical Alvarez lenses. We demonstrate that the suggested operation principle is compatible with confocal microscopy. In order to optimize the system, we have drawn advantage of the flexibility a liquid-crystal spatial light modulator offers for the implementation. For given specifications, dedicated diffractive optical elements or freeform elements can be used in combination with resonant galvo-scanners or acousto-optic beam deflectors, to achieve even faster z-scans than reported here, reaching video rate.
ABSTRACT
The nucleophilic substitution reaction CN(-) + CH3I allows for two possible reactive approaches of the reactant ion onto the methyl halide, which lead to two different product isomers. Stationary point calculations predict a similar shape of the potential and a dominant collinear approach for both attacks. In addition, an H-bonded pre-reaction complex is identified as a possible intermediate structure. Submerged potential energy barriers hint at a statistical formation process of both CNCH3 and NCCH3 isomers at the experimental collision energies. Experimental angle- and energy differential cross sections show dominant direct rebound dynamics and high internal excitation of the neutral product. No distinct bimodal distributions can be extracted from the velocity images, which impedes the indication of a specific preference towards any of the product isomers. A forward scattering simulation based on the experimental parameters describes accurately the experimental outcome and shows how the possibility to discriminate between the two isomers is mainly hindered by the large product internal excitation.
