Femtosecond laser-based phase-shifting interferometry for optical surface measurement
Yue Wang1, Shilin Xiong1, Guanhao Wu1
1State Key Laboratory of Precision Measurement Technology and Instruments, Department of Precision Instrument, Tsinghua University, Beijing 100084, China.
The Review of Scientific Instruments
|December 4, 2018
Summary
This study presents a novel interferometer for precise optical surface measurement. It uses a femtosecond laser and frequency sweeping to eliminate mechanical scanners, achieving high accuracy.
Area of Science:
- Optical Metrology
- Interferometry
- Femtosecond Laser Technology
Background:
- Precise optical surface measurement is crucial for various scientific and industrial applications.
- Traditional interferometers often rely on mechanical scanning, limiting speed and introducing errors.
- Femtosecond lasers offer unique properties for high-resolution measurements due to their short pulse duration and low temporal coherence.
Purpose of the Study:
- To demonstrate a novel unequal-path phase-shifting interferometer for precise optical surface measurement.
- To eliminate the need for mechanical scanning devices in interferometers.
- To achieve high accuracy in surface profile reconstruction.
Main Methods:
- Utilizing the periodic low temporal coherence of a femtosecond laser for phase shifting.
- Scanning the relative time delay by sweeping the laser repetition frequency.
- Employing an iterative least-squares fitting algorithm for phase derivation.
- Setting the optical path length difference to integer multiples of the pulse interval.
Main Results:
- Successful reconstruction of a glass slide surface profile.
- Demonstrated agreement between the novel interferometer and a commercial Fizeau interferometer.
- Achieved a peak-to-valley difference of 0.050 μm compared to the commercial system.
Conclusions:
- The developed unequal-path phase-shifting interferometer enables precise optical surface measurement without mechanical scanners.
- The method leverages femtosecond laser properties and advanced algorithms for accurate phase retrieval.
- This technique offers a promising alternative for high-accuracy optical metrology.
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