1,721,125 research outputs found
Corrections of the travelling-fringe period for the interference of aberrated beams
Full text linkWhen laser beams are used for length measurements by interferometry and the realisation of the meter, they are approximated by plane waves. Hence, from the measured frequency, the dispersion relation of plane waves gives the wavelength in a vacuum and, consequently, the period of the interference signal. However, this relation does not hold exactly and the wavelength is not a well-defined quantity. Aberrations of the wavefront and intensity profile bias the phase accumulation and originate measurement errors. This paper gives the corrections for the period of the integrated interference of aberrated paraxial beams
Defocused travelling fringes in a scanning triple-Laue X-ray interferometry setup
Full text linkThe measurement of the silicon lattice parameter by a separate-crystal triple-Laue X-ray interferometer is a key step for the realization of the kilogram by counting atoms. Since the measurement accuracy is approaching nine significant digits, a reliable model of the interferometer operation is required to quantify or exclude systematic errors. This paper investigates both analytically and experimentally the effect of the defocus (the difference between the splitter-to-mirror and analyser-to-mirror distances) on the phase of the interference fringes and the measurement of the lattice parameter
Coupling of wavefront errors and pointing jitter in the LISA interferometer: misalignment of the interfering wavefronts
Full text linkThe laser interferometer space antenna is a foreseen space-based gravitational wave detector, which aims to detect 10^−20 strains in the frequency range from 0.1 mHz to 1 Hz. It is a triangular constellation of three spacecraft, with equal sides of 2.5 × 10^9 m, where every spacecraft hosts a pair of telescopes that simultaneously transmit and receive laser beams measuring the constellation arms by heterodyning the received wavefronts with local references. Due to the spacecraft and constellation jitters, the interfering (received and local) wavefronts become misaligned. We investigate analytically the coupling between misalignments and aberrations of the interfering wavefronts and estimate the relevant contribution to the noise of the heterodyne signal
Coupling of wavefront errors and jitter in the LISA interferometer: far-field propagation
Full text linkThe Laser Interferometer Space Antenna (LISA) is a gravitational wave detector, which aims to detect 10−20 strains in the frequency range from 0.1 mHz to 0.1 Hz. It is a constellation of three spacecrafts, an equilateral triangle with side length of m, where interferometry monitors the spacecraft distances. Aberrations and jitter of the wavefront sent by a spacecraft to the next combine to cause a measurement noise. The paper investigates analytically this coupling, including beam clipping and far-field propagation, and develops criteria for the assessment of the wavefront quality. It also gives the results of Monte Carlo simulations of the measurement noise for arbitrary wavefront aberrations and jitters
The LISA interferometer: impact of stray light on the phase of the heterodyne signal
Full text linkThe Laser Interferometer Space Antenna is a foreseen gravitational wave detector, which aims to detect 10−20 strains in the frequency range from 0.1 mHz to 0.1 Hz. It is a triangular constellation, with equal sides of m, of three spacecraft, where heterodyne interferometry measures the spacecraft distances. The stray light from the powerful transmitted beam can overlap with the received one and interfere with the heterodyne signal. We investigated the contribution of random phase variations of the stray photons to the noise of the heterodyne signal. A balanced detection scheme more effectively mitigates this adverse effect than a separation of the frequencies of the transmitted and local radiation. In the balanced scheme, in order to limit the phase noise to picometer level, the incoherent power of the stray light must be kept below about 10 nW W−1 for an asymmetry of the recombination beam splitter of 1%
Gravitational and Coriolis forces in crystal neutron interferometry. I. Theory
Full text linkThe proof that neutron interference is possible using split-crystal interferometers opens the way to extended arm separation and length and to new experiments exploring quantum mechanics and gravity. Therefore, this paper reexamines the effect of gravitational and Coriolis forces on the Laue diffraction of neutrons by perfect crystals and the operation of crystal interferometers. We give in analytical form the transfer matrices for the propagation of the neutron quantum state, either pure or mixed and subjected to gravity and Coriolis force, in free space and perfect crystals. They are used to study the effect of interferometer aberrations on the quantum-mechanical phase due to the Earth's gravity. We also give an alternative way to understand the impact of gravitational and Coriolis forces in terms of the crystal displacements and tilts perceived by the neutron
Gravitational and Coriolis forces in crystal neutron interferometry. II. Numerical simulations
Full text linkPrevious studies have proven that neutron interference using split-crystal interferometers is possible. This proof paves the way for extended arm separation and length, opening the doors to new experiments exploring quantum mechanics and gravity. In a previous publication, we took a closer look at how gravitational and Coriolis forces affect dynamical diffraction in crystal interferometry. This paper uses the formalism developed, which allows for extended capabilities in studying the interferometer operation, to investigate numerically the contributions to the neutron phase of geometrical aberrations and dynamical diffraction. In addition, this work explores an alternative geometry, with the interferometer operated vertically, to determine the gravitationally induced quantum-mechanical phase independently of the dynamical diffraction and self-weight bending of the interferometer
Measurement of miscut angles in the determination of Si lattice parameters
Full text linkThe measurement of the angle between an interferometer's front mirror and the diffracting planes is a critical aspect of the measurement of Si lattice parameters by combined x-ray and optical interferometry. In addition to being measured offline by x-ray diffraction, it was checked online by moving the analyser crystal transversely and observing the phase shift of the interference fringe. We describe the measurement procedure and give the miscut angle of the Si-28 crystal, whose lattice parameter was an essential input datum for the determination of the Avogadro constant in the past and which is now used in the definition of the kilogram, based on counting atoms. These data will benefit others that might wish to repeat the measurement of the lattice parameters of this unique crystal
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