Operation model of a skew-symmetric split-crystal neutron interferometer.

The observation of neutron interference using a triple Laue interferometer formed by two separate crystals opens the way to the construction and operation of skew-symmetric interferometers with extended arm separation and length. The specifications necessary for their successful operation are investigated here: most importantly, how the manufacturing tolerance and crystal alignments impact the interference visibility. In contrast with previous studies, both incoherent sources and the three-dimensional operation of the interferometer are considered.

Fake tilts in differential wavefront sensing.

Two-beam interferometry is a tool of high-precision length-metrology, where displacements are measured to within sub-nanometer resolution and accuracy. Differential wavefront sensing - via phase detection by segmented photodiodes - adds the capability of simultaneously measuring the target translation and rotation. This paper gives an analytical model explaining the observation of fake tilts by a combined x-ray and optical interferometer.

Discrete-dipole approximation on a rectangular cuboidal point lattice: considering dynamic depolarization.

Discrete-dipole approximation (DDA), which is used for computing scattering and absorption by particles of arbitrary geometry and material, is extended to the case of a rectangular cuboidal point lattice using an accurate, analytical expression of the polarizability of each cuboidal element at optical frequencies of up to 100 nm in size. This polarizability formulation (cuboidal lattice with depolarization or CLD) is shown to be more accurate in the computation of the extinction, scattering, and absorption cross sections when simulating dielectrics compared to other available and commonly used expressions of the polarizability. This can be used to reduce the number of dipoles N used, and therefore, the computation time while achieving the same accuracy of other formulations.

Observation of a bent crystal-lattice by x-ray interferometry.

he capability of operating a separate crystal x-ray interferometer over centimeter displacements has made it possible to observe minute strain fields of a bent crystal at the atomic scale resolution by means of phase-contrast x-ray topography. Measurement and predictive capabilities of lattice strain are key ingredients of a highly accurate measurement of the Si lattice parameter and of a determination of the number of atoms in a realization of the mass unit based on an atom mass. Here we show that the observed strain can be accurately predicted by a finite-element analysis of the crystal deformation.

Si lattice parameter measurement by centimeter X-ray interferometry.

A combined X-ray and optical interferometer capable of centimeter displacements has been made to measure the lattice parameter of Si crystals to within a 3 x 10(-9) relative uncertainty. This paper relates the results of test measurements carried out to assess the capabilities of the apparatus.

Aberration effects in two-beam laser interferometers.

In displacement measurements by two-beam interferometers, the wavefront curvature of a laser beam causes a systematic increase of the fringe period. This increase depends on beam collimation: It is null for a plane wave and proportional to the squared divergence of the beam. With interfering beams not perfectly recombined, an additional fringe-period error is caused, with the effect of counteracting and also of compensating for and prevailing over the usual error.