The use of x-ray interferometry to investigate the linearity of the NPL Differential Plane Mirror Optical Interferometer

Abstract

The x-ray interferometer from the combined optical and x-ray interferometer (COXI) facility at NPL has been used to investigate the performance of the NPL Jamin Differential Plane Mirror Interferometer when it is fitted with stabilized and unstabilized lasers. This Jamin interferometer employs a common path design using a double pass configuration and one fringe is realized by a displacement of 158 nm between its two plane mirror retroreflectors. Displacements over ranges of several optical fringes were measured simultaneously using the COXI x-ray interferometer and the Jamin interferometer and the results were compared. In order to realize the highest measurement accuracy from the Jamin interferometer, the air paths were shielded to prevent effects from air turbulence and electrical signals generated by the photodetectors were analysed and corrected using an optimizing routine in order to subdivide the optical fringes accurately. When an unstabilized laser was used the maximum peak-to-peak difference between the two interferometers was 80 pm, compared with 20 pm when the stabilized laser was used.

High temperature measurement and characterisation of piezoelectric properties

“…The system is configured as a dual beam Jamin interferometer [51] (Figure 8) to exploit the fundamental link between the laser wavelength and the change in height of the upper sample surface when an electric field is applied to a piezoelectric sample. The interferometer measures changes in the beam path length between the top surface of the sample and the reference block, enabling evaluation of length changes in the sample due to piezoelectric and thermal strains.…”

Displacement Measurement

“…Differential interferometers can have sub-nanometre accuracies, as has been confirmed using X-ray interferometry [30]. When a Heydemann correction is applied (see Section 5.3.8.5), such interferometers can have non-linearities of a few tens of picometres.…”

“…Examples of the calibration of a differential plane mirror interferometer and an optical encoder can be found in Refs. [30] and [81], respectively. In both cases, periodic errors with amplitudes of less than 0.1 nm were measured once a Heydemann correction (see Section 5.3.8.5) had been applied.…”

A nano-metrology system with a two-dimensional combined optical and X-ray interferometer and an atomic force microscope

“…The X-ray interferometer, which was made from a nearly perfect Si (220) crystal, is a major instrument for precision measurement in a nano-scale measuring system (Basile et al 1994;Cavangnero et al 2004;Yacoot and Downs 2000;Yacoot and Cross 2003;Becker et al 1981). The periodic signal that is generated from an X-ray interferometer is about 0.192 nm.…”