During the last decade a number of volume holographic media have been investigated that could serve not only as diffractive optical elements (DOEs) for light but also for slow neutrons. In this contribution we discuss the light optical properties of a stack of two gratings separated by an optically inert slice recorded in a Bayfol®HX photopolymer. While the refractive-index modulation of the gratings for light is remarkable, the corresponding neutron optical analogue is, so far, in the medium range of other materials investigated. We therefore aim at possible improvements which are discussed in this manuscript.
We demonstrate for the first time the use of nanodiamond in constructing holographic nanoparticle-polymer composite transmission gratings with large saturated refractive index modulation amplitudes at both optical and slow-neutron wavelengths, resulting in efficient control of light and slow-neutron beams. This is so because nanodiamond possesses a high refractive index at optical wavelengths and large coherent and small incoherent scattering cross sections with low absorption at slow-neutron wavelengths. In the first part of the work we describe the synthesis of nanodiamond, the preparation of photopolymerizable nanodiamond-polymer composite films, the construction of transmission gratings in nanodiamond-polymer composite films and light optical diffraction experiments. Experiments of slow-neutron diffraction from such gratings will be described in the second part.
In the second part of our presentations we discuss the results of diffraction experiments from nanodiamond-polymer composite gratings performed with slow neutrons, i.e., at wavelengths longer than a nanometer. One goal of our investigations is to develop flexible, handy, low cost neutron diffractive optical elements (gratings) which can be tailored to serve as mirrors, two-port beamsplitters, multiport beamsplitters, polarizing beamsplitters or even can be assembled to form an interferometer. Basically three adjustable multiplicative parameters are decisive for the performance, i.e., the reflectivity or diffraction efficiency, of such gratings: the wavelength of the neutrons, the thickness and the neutron scattering density modulation of the grating. While the _rst is solely determined by the application one has in mind, the second parameter can be adjusted during the production process of the sample or by tilting the grating about an axis parallel to the grating vector, thus increasing the effective thickness. The third parameter, however, can only be tuned via the production process of the gratings but offers an enormous flexibility due to a variety of nanoparticles and the polymeric host materials at hand. For neutrons the important criteria are to design gratings having high coherent scattering length density modulation while avoiding incoherent scattering and absorption at the same time. For interferometric purposes an ideal grating will have high reflectivity and low angular selectivity. Here, we show first results obtained with nanodiamond-polymer composite gratings and outline potential ways to improvements.
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