Appl. Phys. A 74 [Suppl.], S320–S322 (2002) / Digital Object Identifier (DOI) 10.1007/s003390201736 Applied Physics A Materials Science & Processing Development of neutron optical components at ILL P. Courtois ∗ , B. Hamelin, H. Humblot, L. Alianelli, F. Pfeiffer Institut Laue Langevin, BP 156, 38042 Grenoble Cedex 9, France Received: 24 July 2001/Accepted: 12 March 2002 –  Springer-Verlag 2002 Abstract. The neutron optics laboratory at ILL carries out an innovative research program in various fields of neutron op- tics with the aim of developing new and improved tools for neutron instrumentation. An overview of some recent high- lights is presented, indicating the breadth of the potential applications. PACS: 61.12.q Although neutron-source fluxes remain modest compared to other scattering techniques, major advances in instrumenta- tion resulting in order of magnitude increases in effective neutron flux are still attainable through the development of improved beam optics and detectors. The improvements in beam optics are obtained both through a better coupling of the optical elements aided by computer simulation and design but also via better control of the, often delicate, manufactur- ing processes. Some examples of the developments carried out at ILL in various fields of neutron optics are given in the following sections. 1 Crystal optics In order to compensate for the low source flux densities neutron beam lines use the large phase space volumes pro- duced by deformed crystals. Although bent perfect crystals are finding more applications in the neutron world, tradition- ally mosaic crystals are employed despite the large angular divergences that are transmitted. The recent development of the “onion peel” method at ILL [1] to construct controlled, artificial, mosaic crystals has been extremely successful for the production of copper monochromators which maintain the out of plane crystal perfection hence allowing efficient focussing. Gradient crystals on the other hand increase the phase space volume by accepting a larger wavelength spread while maintaining a small beam divergence. Recently mixed Cu-Ge crystals have been successfully grown in the ILL ∗ Corresponding author. (Fax: +33-476/207-700, E-mail: Courtois@ill.fr) optics laboratory with a smooth variation in the d -spacing, Δ d/d ∼ 2.10 -3 . It is now possible to combine the gradient and mosaic properties of crystals to produce a well-tailored phase space volume. However in order to model the per- formance of these newly available crystal elements and to couple them efficiently to other elements of a neutron beam line it has been necessary to develop the detailed physical models for numerical simulations. We have made extensive calculations and measurements of the temperature dependent reflectivities of mosaic crystals to produce realistic values for crystal parameters serving as a data base for further simu- lations (see Table 1 and [3]). Following this work a neutron version of the X-ray community’s optics calculation program XOP [4] will be released in the near future. ILL also produces Heusler single crystals with a con- trolled mosaicity for polarised neutrons [5]. Recently the largest Heusler polarising monochromator ever built (dimen- sions: 230 × 150 mm 2 ) was installed on IN20 allowing al- most an order of magnitude increase in polarised neutron flux [Fig. 1] [6]. The high order λ/2 contamination and the relatively large d -spacing of Heusler crystals limit their use for some applications. Development of new polarising crystal alloys is in progress at ILL. 2 Multilayers In addition to the traditional uses of multilayers including supermirrors, wide band reflectors and polarisers, we have Table 1. Neutron absorption coefficient μ and peak reflectivity of a copper mosaic sample of thickness d = 0.8 cm at 48 meV. The reflection used is the <220> in symmetric Laue geometry. Freund’s formulas have been used for calculating μ Temperature μ calc μ fit calculated measured Kelvin cm -1 cm -1 Refl. Refl. 77 0.307 0.2735 0.388 0.317 115.5 0.3275 0.306 0.376 0.302 187.3 0.368 0.345 0.363 0.289 232.8 0.3935 0.366 0.356 0.279 288.9 0.424 0.396 0.346 0.271