Utilizing an optical holographic setup thick refractive index gratings are written in poly (methyl methacrylate) (PMMA). We show experimentally that these gratings diffract not only visible light but also cold neutrons.PACS numbers: 61.12. Gz, Holographic methods are a well established tool for the investigation of photorefractive materials, i.e., materials which change their refractive index upon illumination. 1 Certain photorefractive processes like thermal fixing 2 or photopolymerization 3 involve mass transport. As a consequence, not only the optical but also the neutron refractive index may be changed. We report here, for the first time, on neutron diffraction at thick gratings produced by optical holography.Our sample was a 1.93-mm-thick plate (approximately 25x25 mm 2 ), consisting of a poly (methyl methacrylate) (PMMA) matrix, residual monomer, and the photoinitiator bis(cyclopentadienyl)-titaniumdichloride. When illuminating the sample with the light interference pattern of two coherent plane waves of optical wavelength X =514.5 nm, a photochemical reaction is started. In the course of the chemical reaction diffusion processes take place which build up a mass-density modulation in conformity with the intensity modulation of the light interference pattern. This mass-density modulation is the origin of the optical and neutron refractive-index grating. By an optical diffraction experiment with X =632.8 nm the grating period A has been determined to be 361.7 dz 0.1 nm. The grating-containing area of the sample has an elliptical form with extensions 10x18 mm 2 .The neutron diffraction experiment was performed at the Dll small-angle scattering instrument of the Institute Lau-Langevin (ILL) at Grenoble, France. For our test experiment two hours of beam time were provided.Wavelength selection at the instrument Dl 1 is done by setting the rotary speed of a mechanical monochromator drum. 4 A speed of 1832 rpm, as used in our experiment, yields a wavelength distribution with a full width at half maximum of 0.09 nm. According to Ref. 4 the neutron wavelength at the maximum is theoretically X" = 1.025 and experimentally X n = 1.01 ±0.01 nm; according to Ref. 5, X"=1.00 and 0.98 nm, respectively. The uncertainty is partly due to a slight misalignment of the drum's rotary axis.The sample was placed in the collimated neutron beam (beam divergence -0.05°) behind a cadmium dia-phragm with a clear aperture of 8x11 mm 2 . The diaphragm ensured that neutrons could pass through only the grating-containing area of the sample. The distance between the detector (64x64 10 BF 3 gas-containing cells of 100-mm 2 cross section) and the sample was 35 m.In order to eliminate the effect of gravity on the diffraction pattern the sample was mounted such that the Bragg peaks were to be expected in the horizontal plane. Therefore, the grating vector K of the refractive-index grating also has to be in the horizontal plane (x-y plane in Fig. 1). By turning the sample around a vertical axis (z axis in Fig. 1), the inclination angle a between t...

Holographic gratings are written in copper-doped LiNbO3 crystals at temperatures of about 180 degrees C. At room temperature the gratings are fixed. The subsequent development process under homogeneous illumination is investigated by the microphotometric method. Measurements of the light intensity pattern at the exit face of the crystal reveal not only the change of the amplitude but also a phase shift of nearly pi . The dynamics of the development process can be fully understood by the assumption of a quasi-permanent modulated charge distribution and a second modulated charge distribution of optically excitable ions.

We report on significant improvements of the performance of thick diffraction gratings for cold neutrons. The basis material for the production of holographic gratings by optical means is photosensitized deuterated poly(methy1 methacrylate) (D-PMMA). The properties of these gratings now approach those of perfect monochromator crystals for neutrons of shorter wavelength: for cold neutrons with 1.0nm wavelength the gratings exhibit a reflectivity in the percent range which makes them suitable for a wide range of applications in neutron optics.

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