Differential laser interferometer for nanometer displacement measurements
Journal
AIAA Journal
Journal Volume
33
Journal Issue
9
Pages
1675-1680
Date Issued
1995
Author(s)
Abstract
A dual beam differential laser interferometer/vibrometer measurement system was developed for studying the steady-state and dynamic behavior of low-weight high-performance mechanical systems. This newly developed optical system employs many optical and mechanical design tactics to achieve design targets such as nanometer displacement accuracy, ease of use, capability of measuring untreated structural surfaces, high-measurement band- widths, and large-dynamic ranges. Both the optical/mechanical configurations and the design approaches adopted are discussed in detail. A flying slider and thin-film disk system currently used in the disk drive industry were used as the testbed to verify the capabilities of this newly developed nanometer structural displacement/velocity measurement system. a specular reflec- tive surface on the measurement surface as these interferometry systems will not function properly unless the wave front quality of this reflective surface is within a fraction of the laser wave- length used. This tight wave front requirement typically requires a high-quality mirror or a retroreflector to be added to the mea- surement surface. The weight of this added optical surface and its mounting fixture places a stringent constraint on adopting conven- tional interferometer systems to be used to examine general struc- tural performances, especially the dynamic behavior of lightweight structures. As lightweight, high-performance precision structures become more and more an integral and necessary part of to- day's high-technology systems, whether in aerospace structures or in precision machining tools, a new and better measurement system will be needed to further advance the field of precision mechanics. A newly developed differential laser interferometer/vibrometer that adopts the Doppler principle, phase/frequency decoding al- gorithm, and balanced mechanical design to achieve noncontact differential and absolute displacement/velocity measurements of opaque objects will be discussed in this paper. Unlike the tradi- tional laser interferometer, displacement of untreated surfaces can now be measured because of the newly designed optical configura- tion. The fringe interpretation schemes used provide phase decoding accuracy corresponding to fractions of a nanometer displacement. A novel balanced mechanical design was also developed for flex- ibility in alignment and for insensitivity to interferomete r arm fix- ture thermal deformation induced measurement noise. With this balanced mechanical design and the new optical configuration
SDGs
Type
journal article