Neutron reflection is perhaps the most developed branch of slow neutrons optics, which in itself is a direct consequence of the undulatory nature of the neutron. After reviewing the basic types of interactions (nuclear and magnetic) between neutrons and matter, the formalism is introduced to calculate the reflectivity from a sample composed of stacked flat layers and, inversely, to calculate the stacking from reflectivity measurements. Finally, a brief survey of the applications of neutron reflection is given, both in technology and in fundamental research.

Very high reflectivity (some 95 % or better) supermirrors, with cut-off angles up to 2 times the critical angle of Ni coated simple total reflection neutron mirrors, can be produced using well established conventional deposition techniques. This performance makes applications involving multiple reflections and transmission geometries feasible, which in turn allow us to use more sophisticated neutron optical systems in order to optimize performance and minimize the amount a scarce supermirrors required. A key feature of several of these novel systems is the distribution of tasks between the several optical components achieving the desired performance by multiple action. The design and characteristics of a series of novel applications, such as polarizing cavities, collimators and guides, non-polarizing guides, beam compressors, deflectors and splitters (most of them tested or being implemented) are the main subjects of the present paper.

In this article, I describe a calculation of the properties of a straight supermirror guide and present details of the supermirror polarising "benders" fabricated at the Institut Laue Langevin in Grenoble, France.

We present a new method of designing supermirrors, based on considering the contribution of each bilayer to the extinction in a given stack of bilayers, and derive and solve the discrete equations governing the choice of layer thicknesses. In the limit of zero layer thickness, the usual continuum result is recovered. The design, which can produce essentially perfect reflectivity over the entire supermirror range, also provides an objective physical mechanism for trading reflectivity to gain angular range.

The fabrication of high reflectivity multilayer minochromators usually involves depositing a greater number of bilayers than the calculated number for perfect multilayers. This deviation from ideal behavior occurs due to the presence of imperfections in layers. These imperfections are strongly dependent on the deposition process employed and the parameters during deposition. An understanding of the types of imperfections present may lead to attempts to minimize them. The imperfections should be taken into consideration for determining the sequence of d-spacing for making a supermirror.

Analysis of Ni-Ti multilayer neutron reflectors and supermirrors has been undertaken to identify the causes of the lower than expected observed scattering power and critical angle enhancement of Ni-Ti supermirrors. Results of these investigations have focused attention on cusp formation in the Ni-Ti bilayers as probable cause for the reduced neutron scattering power. Grazing angle x-ray and neutron scattering, wide angle neutron diffraction and analytical cross sectional TEM have been used in this investigation. The multilayers were produced by magnetron sputtering and ion-beam deposition on float glass substrates and silicon wafers.

We installed the first nickel mirror neutron guide tube with a characteristic wavelength of 2.85 Å at Kyoto University research reactor(KUR, 5MW, cooled and moderated by light water) in 1973 and a supermirror guide tube with a characteristic wavelength of 1.17 Å in 1984, in order to get more intense thermal neutron beam. Four guide tubes are under construction at a cold neutron source installed in 1986. Two of them are supermirror type with a characteristic wavelength of 3 Å and the others are supermirror and Ni-mirror type with characteristic wavelengths of 6 Å and 23 Å, respectively. Supermirrors are made by automatically controlled vacuum deposition of nickel and titanium metal with electron gun. Their averaging reflectivity for the first supermirror guide tube are the following: The apparent critical wavelength, λ/θ, of reflection is 240 Å in term of wavelength(λ/θ) corresponding to the component of wave number perpendicular to the mirror surface. The reflectivity is 0.65 at the apparent critical wavelength and becomes higher with increasing neutron wavelength up to nearly unity for wavelength longer than 500 Å. Supermirror guide tubes are featured by more available neutrons with larger divergent angles and shorter length of the guide tubes. These features would bring us significant advantages depending on experimental requirements.

During 21 years of work in Neutron Guide Manufacturing, we were involved in every European Neutron Scattering Facilities, totalizing almost 3 km of guides. We recall simple formulas giving losses in neutron flux, which correlation with every parameters of manufacturing and setting up process, allowed us a step by step improvement of efficiency. After a brief description of our design, we describe some special devices which optimize the whole installation . We now currently use 58 Nickel for the reflecting material, and are keenly looking toward new materials and Super-Mirror coating.

The new neutron guide laboratory ELLA at the JUlich research reactor started its full operation at the beginning of this year. The guide system supplies 10 instruments with cold neutrons from the rebuilt hydrogen cold source. We present a description of the technical layout of the guide system. In order to achieve a larger solid angle, the guides were covered with isotopically pure 58Ni. The obtained neutron fluxes will be quoted. In addition, special beam forming devices were installed, namely a neutron guide junction at the entrance of the guide system, a multislit-bender with a radius of curvature of only 57 m, which achieves a large beam separation, and conical focusing neutron guides with supermirror layers to increase the flux at the sample position.

A straightforward method, based on phase space arguments, is presented to calculate the neutron flux gains which may be achieved using a section of converging guide following a straight guide.

If properly designed, converging guides may be used to increase the current density of neutrons in a beam from a parallel neutron guide. The disadvantage of this type of device is that there is an increase in beam divergence. The spatial and angular distributions of the beam emerging from a converging guide are generally nonuniform, and the performance of the guide is dependent on the neutron's wavelength. Analytic and numerical methods of calculation are briefly discussed, and the results of selected Monte Carlo numerical calculations are presented. Measurements on a scaled down version of a converging guide system are reported and found to compare well with calculation.

Neutron mirror reflection is based on the phenomenon of total reflection of thermal neutrons discovered more than 40 years ago by Fermi and Zinn. Since Maier-Leibnitz and Springer's original proposal 30 years ago neutron mirror reflection has been widely used for beam channeling through guide tubes. Neutron mirrors are essential components for Doppler-shifting turbines as well as in high-resolution spectrometers for ultracold neutrons. We describe instrumentation making ample use of imaging mirrors for beam preparation and for neutron microscopy. The paper also reports a detailed analysis of specular and non-specular components in mirror reflection and transmission. Experimental reflection profiles are compared to those of zero-order diffraction from a planar ruled diffraction grating, and we scrutinise further "textbook experiments" testing the wave properties of neutrons.

Ultracold neutron facility with applied neutron optics consisting of a deuterium cold source, curved nickel mirror guide tube for very cold neutrons, a supermirror turbine for ultracold neutron production and a gravity spectrometer for high resolution scattering experiments with ultracold neutrons are described here with their characteristic performances.

We reconsider the possibilities of neutron focusing with mirrors, in particular for the applicability in the field of Small Angle Neutron Scattering (SANS). Focusing SANS-instruments are compared with the Dll-like pinhole instrument at the Grenoble reactor and with a Bonse-Hart-type Double Crystal Diffractometer (DCD). From intensity calculations and experimental intensity profiles it can be concluded that focusing SANS-instruments with high quality neutron mirrors will be superior to conventional pinhole instruments in the regime of a high scattering vector resolution δQ ≤ 10-3 Å-1. In addition, experiments with a neutron "lens" and a microbender consisting of microguides are presented.

It is expected that thin-film mirrors, multilayers and supermirrors will play an important role as optical elements to transport, focus, monochromate, and polarize neutrons at the cold neutron research facility which is presently under construction at the National Bureau of Standards. In this paper, specific applications of these reflecting devices to three instruments, a spin-polarized, inelastic scattering spectrometer with novel, adjustable resolution properties, a focussing small angle scattering machine, and a neutron reflectometer will be described.

A multilayer neutron monochromator and polarizer of double mirror type have been developed using a successive double reflection by two multilayer mirror deposited on a Si substrate. The multilayer mirrors have a supermirror-type thickness distribution of bilayers. The monochromator (polarizer) plays simultaneously the roles of a monochromator (polarizer), a collimator and a beam bender through a successive double reflection by the two mirrors. The double reflection brings a low contamination of higher order Bragg reflections. For the monochromator several multilayer mirrors deposited on Si substrates are assembled in the shape of Soller slit to cover a wide neutron beam. The multilayer mirrors for the monochromator are fabricated by depositing Ni and Ti. The bilayer thickness distribution is supermirror-type with the mean thickness of 150 Å and the width of the distribution of 20%. The monochromator provides a monochromatic beam of 5 Å with wavelength resolution of 20%, divergent angle of 1/300 rad and bent angle of 1/15 rad. Peak reflectivity of the monochromator is observed to be 40% for a incident beam with a divergence of 1/240 rad. Available beam size is about 5 cm x 1 cm in a Soller-slit type with 12 sheets of the multilayer mirrors. FeCo-Ti multilayer polarizer and FeCo -V multilayer analyzer have the similar characteristics with the Ni-Ti multilayer monochromator. The polarizing efficiency is about 90%.

Thin-film multilayer reflectors for polarizing neutrons have been fabricated by sputtering bilayers of ferromagnetic iron (Fe) and non-magnetic silicon (Si) onto flat glass substrates. The multilayers were deposited according to the independent variation of one of four parameters: number of bilayers; bilayer thickness (D-spacing); argon sputtering gas pressure; and target power. The relationship between the measured neutron reflectivities of these multilayers and the expected theoretical values is discussed with respect to the deposition parameters.

Beam defining devices used for synchrotron X-ray and neutron scattering techniques have both common and different aspects. For instance, a common feature is that Bragg diffraction by single crystals is used to define the energy and the energy spread of beams and that similar focusing schemes apply to both neutron and X-ray optics. The scattering amplitudes of many materials are of the same order of magnitude for X-rays and neutrons giving rise to similar performances of the optical devices. On the other hand, the generally low absorption for neutrons compared to that for X-rays of the same wavelength lead to specific differences between both techniques. Besides these intrinsic interaction properties of the two radiations with matter, the properties of the sources are important for the design of beam optics. While neutron scattering is severely flux-limited and thus needs a big source size and beam divergences up to a degree, modern synchrotron X-ray sources are by many orders of magnitude smaller and emit low-divergence beams of very high intensity. As a consequence of this, mosaic crystals are used for neutron monochromatization and perfect crystals are more suitable for synchrotron radiation beams. However, for particular techniques perfect crystals are required also for neutron experiments and mosaic crystals can provide high X-ray fluxes for synchrotron radiation experiments. The problem of radiation heating which is important for synchrotron is inexistent for neutron devices.

This paper gives an overview of soft x-ray monochromators for synchrotron radiation. Showing some typical examples for different energy regions and applications, general design criteria are explained, and specific problems, limitations and future developments using undulator radiation from third generation storage rings are addressed. For a more complete information the reader is referred to various recent review articles.

We have used W/Si multilayers and multilayer/KAP crystal combinations in a double crystal monochromator beamline at BESSY. The throughput in the energy region from 200 to 1600 eV was drastically increased as compared with previous experiments and thus the performance compares favourably with other monochromators using conventional optics in this energy region. XAS spectra of the 2p edges of 3d transition metals are shown. No x-ray induced damage of the multilayers could be detected using Auger depth profile analysis after one week of exposure to the synchrotron beam. AES profiles distinguished up to the first 30 layers. Our XAS results open up the possibility of constructing multielement high resolution soft x-ray monochromators as well as high intensity broadband monochromators.

A simple two-mirror monochromator based on multilayer films has been developed for use with synchrotron radiation. Measurements of the performance of this monochromator and the characterization of a typical component mirror are described.

The theory of the reflecting properties of multi layer neutron monochromators is reviewed. It is shown that both the Bragg reflection and the mirror reflection can be understood, at least qualitatively, within the familiar kinematical theory of neutron scattering. For a detailed quantitative understanding of these phenomena, including such questions as the optimum number of bilayers, the effect of the multiple reflection that is neglected in the kinematical theory must be taken properly into account. The way in which this can be done using the dynamical theory of neutron scattering is indicated.

The neutron reflectivity spectra of multilayers has been measured as a function of angle of incidence and neutron wavelength in the range 1-7Å. The measurements are discussed in terms of the fabrication method employed and compared with the corresponding X-ray reflectivity spectra.