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Measurement of changes in optical path length and reflectivity with phase-shifting laser feedback interferometry
1Department of Mechanical and Aerospace Engineering, Case Western Reserve University, Cleveland, Ohio 44106, USA.
Applied Optics
|March 6, 2008
Summary
This study presents a novel phase-shifting interferometer capable of measuring nanometer-scale displacements with high precision. The sensitive optical instrument is ideal for analyzing subtle sample movements in various scientific applications.
Area of Science:
- Optical physics
- Interferometry
- Nanotechnology
Background:
- Phase-shifting interferometry is a key technique for precise optical measurements.
- Existing interferometers face limitations in sensitivity and sample reflectivity requirements.
Purpose of the Study:
- To present the operating characteristics of a novel phase-shifting interferometer.
- To demonstrate its high sensitivity and application in measuring small displacements.
Main Methods:
- Utilized a continuous-wave (cw) Helium-Neon (He-Ne) laser cavity.
- Introduced phase shifts using an electro-optic modulator.
- Calculated phase and fringe visibility from overdetermined intensity measurements.
Main Results:
- Achieved high sensitivity, measuring displacements below 1 Hz with a root-mean-square (rms) error of approximately 1 nm.
- Demonstrated successful operation with a low-reflectivity sample (3%).
- Applied the interferometer to measure cantilever bending in a piezoelectric bimorph.
Conclusions:
- The novel phase-shifting interferometer offers exceptional sensitivity for displacement measurements.
- It is effective even with samples exhibiting low optical reflectivity.
- The technology is suitable for precise analysis of micro-scale mechanical deformations.
