Applied Optics · 1987 · 259 citations · 5 references
To improve measurement precision, the authors eliminate single‑wavelength phase ambiguities by using equivalent‑wavelength results to determine fringe orders. The method applies two‑wavelength phase‑shifting interferometry on a microscope, synthesizing an equivalent wavelength λeq = λaλb/|λa–λb| by subtracting phase data at visible wavelengths λa and λb, and then resolving phase ambiguities to establish fringe orders. The technique achieves an rms repeatability of λ/1000 at the equivalent wavelength, yielding a dynamic range of 10⁴, as demonstrated on an optical waveguide and a deeply modulated grating.
Two-wavelength phase-shifting interferometry is applied to an interference phase-measuring microscope enabling the measurement of step features. The surface is effectively tested at a synthesized equivalent wavelength λeq = λaλb/|λa − λb| by subtracting phase measurements made at visible wavelengths λa and λb. The rms repeatability of the technique is λ/1000 at the equivalent wavelength. To improve the precision of the data, the phase ambiguities in the single-wavelength data are removed using the equivalent wavelength results to determine fringe orders. When this correction is made, a measurement dynamic range (feature height/rms repeatability) of 104 is obtainable. Results using this technique are shown for the measurement of an optical waveguide and a deeply modulated grating.
5
Two-wavelength phase shifting interferometry
Yeou-Yen Cheng, James C. Wyant · Applied Optics · 1984 · 428 citations