Tunable phase-extraction formulae for simultaneous shape measurement of multiple surfaces with wavelength-shifting interferometry

The University of Tokyo, Tōkyō, Japan
Optics Express (Impact Factor: 3.49). 12/2004; 12(23):5579-94. DOI: 10.1364/OPEX.12.005579
Source: PubMed


The interferometric surface measurement of single or stacked parallel plates presents considerable technical difficulties due to multiple-beam interference. To apply phase-shifting methods, it is necessary to use a pathlength-dependent technique such as wavelength scanning, which separates interference signals from various surfaces in frequency space. The detection window for frequency analysis has to be optimized for maximum tolerance against frequency detuning due to material dispersion and scanning nonlinearities, as well as for suppression of noise from other frequencies. We introduce a new class of phase-shifting algorithms that fulfill these requirements and allow continuous tuning of phase detection to any frequency of interest. We show results for a four-surface stack of nearparallel plates, measured in a Fizeau interferometer.

2 Reads
  • [Show abstract] [Hide abstract]
    ABSTRACT: Wavelength-shifting interferometry can distinguish in frequency space interference signals from different surfaces, and therefore allows the measurement of optical thickness variation between several quasi-parallel surfaces of a composite transparent object. Frequency analysis of the signal spectrum with a tunable phase-shifting formula can then detect the phase of the individual signals. We have devised a tunable phase-shifting method which uses a freely adjustable number of intensity samples and can be adapted to any frequency spectrum. To extract the signal reliably, two properties of the phase-shifting method are particularly important: it should suppress cross-talk from unwanted frequencies, and it should allow for some variation in the signal frequency. We show that a carefully designed sampling function envelope will combine these benefits, and demonstrate the technique in measurements of three different composite objects each consisting of three reflecting surfaces. The importance of phase-shift linearisation is discussed, and methods for selecting optimal set-up parameters are given.
    Optics and Lasers in Engineering 02/2007; DOI:10.1016/j.optlaseng.2005.12.009 · 2.24 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We proposed and developed an optical system for imaging of the surface profiles of biological cells and tissues with nanometer resolution. The system is a low-cost system which can perform the imaging of the surface morphology in a large area and large depth range without any special preparation of the sample. The system consists of two interferometers in which one is in the configuration of a Michelson interferometer and the other is in the configuration of a Mach-Zehnder interferometer. The former is used for scanning of the surface profile of the sample, and the latter is used to compensate the phase shift due to the different traveling ranges of the reference mirror in successive scannings. The phase difference between the interferograms detected in both interferometers is proportional to the surface height of the sample at that point. The system was demonstrated to possess the axial resolution within +/-5 nm and its lateral resolution is at the diffraction limit. We used the system for the imaging of various samples including biological cells and tissues. The system was also used for dynamic imaging to observe the morphological change of the surface of biological cells.
    Proceedings of SPIE - The International Society for Optical Engineering 07/2007; DOI:10.1117/12.728108 · 0.20 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We proposed and demonstrated a low-cost optical system for surface profilometry with nanometer-resolution. The system is based on a composite interferometer consisting of a Michelson interferometer and a Mach-Zehnder interferometer. With the proposed phase compensating mechanism, the phase deviation due to the instability of the optical delay system and environmental perturbation can be compensated simultaneously. The system can perform a wide-field imaging in the millimeter range and a measurement with the axial resolution within +/-5 nm without special shielding and protection of the system as well as any special preparation of the sample.
    Optics Express 11/2007; 15(21):13949-56. DOI:10.1364/OE.15.013949 · 3.49 Impact Factor
Show more