Laue Interferometer

Abstract

The wave functions defined in (5.47) to (5.50) are in an appropriate shape to be applied to a Mach-Zehnder-like neutron interferometer (Fig. 6.1). The silicon perfect crystal interferometer [24] provides widely separated coherent beams and has become a standard method for advanced neutron optical investigations. Its operation is based on division of amplitudes by dynamical Bragg reflection from perfect crystals. In the standard version, a monolithic triple-plate system in the Laue transmission geometry is used, which provides a wide beam separation (≥ 5 cm) and a non-dispersive response to the incident neutron beam. The perfect silicon crystal interferometer is extremely useful for fundamental neutron physics studies. For most applications, the standard triple Laue case interferometer is generally the best configuration (Fig. 6.1). It follows from symmetry considerations that the amplitude and the phase of the wave function in the forward (0) direction behind the empty interferometer is composed of equal parts coming from both beams traversing paths I and II. The wave on path I arrives in the ψ 0-beam after having made a transmission (t) in the first crystal (splitter S), a reflection (r) in the second crystal (mirror M) and another reflection (r) in the third crystal (analyzer A). On path II the sequence is (rrt). From symmetry, it follows that these two waves are equal in phase and amplitude, as will be shown below. However, if a phase shifter is put into one of the arms of the interferometer, phase differences between the two paths can be generated, as will be discussed in the next section. 6.1 Wave Functions and Focusing Condition A full analysis of the perfect silicon crystal neutron interferometer requires a detailed description of the coherent wave fields that propagate through the device. The starting point for this analysis is the plane wave dynamical diffraction theory for a symmetric Laue geometry crystal slab, as developed in the previous section. Repeated sequential application of the transmission and reflection functions (5.49) for each of the crystals of the interferometer leads to formulas describing the 0-beam and G-beam wave fields and the