Synthetic-wavelength interferometry improved with frequency calibration and unambiguity range extension.

We improve the accuracy of distance measurements with synthetic-wavelength interferometry by referencing the spectral spacing of the free-running light sources to a high-precision radio-frequency oscillator. In addition, we increase the unambiguity range with a time-of-flight technique. Distances to scattering technical surfaces can be measured with micrometer accuracy and an unambiguity range of 1.17 m. The measurement rate amounts to 300 Hz.

Multiwavelength digital holography with autocalibration of phase shifts and artificial wavelengths.

A novel implementation of lensless multiwavelength digital holography with autocalibration of temporal phase shifts and artificial wavelength is presented. The algorithm we used to calculate the phase shifts was previously proposed [Opt. Lett.29 183 (2004)] and, to our knowledge, is now used for the first time in lensless holography. Because precise knowledge of the generated artificial wavelength is crucial for absolute measurement accuracy, a simple and efficient method to determine the artificial wavelength directly is presented. The calibration method is based on a simple modification of the experimental setup and needs just one additional image acquisition per wavelength. The results of shape measurement of a metallic test object with a rough surface and steep edges are shown and the measurement accuracy is discussed.