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Interference microscopy plays a central role in noncontact strategies for process development and quality control, providing full 3D measurement of surface characteristics that influence the functional behavior of manufactured parts. Here I briefly review the history and principles of this important technique, then concentrate on the details of hardware, software, and applications of interference microscopy using phase-shifting and coherence scanning measurement principles. Recent advances considered here include performance improvements, vibration robustness, full color imaging, accommodation of highly sloped surfaces, correlation to contact methods, transparent film analysis, and international standardization of calibration and specification.

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We describe a system for fast three-dimensional profilometry, of both optically smooth and optically rough surfaces, based on scanning white-light techniques. The system utilizes an efficient algorithm to extract and save only the region of interference, substantially reducing both the acquisition and the analysis times. Rough and discontinuous surfaces can be profiled without the phase-ambiguity problems associated with conventional phase-shifting techniques. The system measures steps to 100 µm, scans a 10µLm range in 5 s, and has a smooth surface repeatability of 0.5 nm.

We propose a computationally efficient theoretical model for low-coherence interferometric profilers that measure surface heights by scanning the optical path difference of the interferometer. The model incorporates both geometric and spectral effects by means of an incoherent superposition of ray bundles through the interferometer spanning a range of wavelengths, incident angles, and pupil plane coordinates. This superposition sum is efficiently performed in the frequency domain, followed by a Fourier transform to generate the desired simulated interference signal. Example applications include white-light interferometry, high-numerical-aperture microscopy with a near-monochromatic light source, and interference microscopy for thickness and topography analysis of thin-film structures and other complex surface features.

Abstract:We demonstrate a millimeter-wave range metamaterial fabricated from cuprate superconductor. Two complementary metamaterial structures have been studied, which exhibit Fano resonances emerging from the collective excitation of interacting magnetic and electric dipole modes.Our interest in superconducting metamaterials is driven by the desire to develop low loss media supporting high quality resonances. Such resonances may be achieved in metamaterials with broken structural symmetry supporting Fano resonances [1] where the quality factor can be controlled by design and is only limited by the Joule losses. Cuprate superconductors show lower surface conductivity than copper at frequencies below 200 GHz even at liquid nitrogen temperatures (see Fig. 1a) and is a prime choice for developing such metamaterials. Here we report the first experimental data on observation of Fano resonances in superconducting metamaterials and demonstrate that their quality factor may be controlled by temperature. All our measurements were performed using a free-space setup, which is based on mm-wave test system equipped with horn antennas (see Fig. 1b) and liquid hellium cryostat.Our metamaterials were fabricated by etching arrays of both positive and negative forms of asymmetrically-split rings in 330 um thick film of high-temperature superconductor YBCO deposited on a low-loss sapphire substrate, as show in Figs. 2a and 2b. Electromagnetic properties of the superconducting structures were studied at temperatures above and below the critical temperature T c = 87.4 K in 75 -110 GHz range of frequencies. Our measurements clearly showed the appearance of the Fano resonances upon superconducting phase transition. The results of the measurements are presented on Figs. 2c and 2d, where we plot changes in the transmission spectra of the cuprate metamaterials with decreasing temperature (down to 77 K) relative to their room temperature state. Fano resonances in metamaterials with broken structural symmetry appear as a result of excitation of the so-called trapped mode (electromagnetic mode that is weakly coupled to free-space [1]), and can be seen to fully develop in

I propose a systematic way to derive efficient, error-compensating algorithms for phase-shifting interferometry by integer approximation of well-known data-sampling windows. The theoretical basi of the approach is the observation that many of the common sources of phase-estimation error can be related to the frequency-domain characteristics of the sampling window. Improving these characteristics can therefore improve the overall performance of the algorithm. Analysis of a seven-frame example algorithm demonstrates an exceptionally good resistance to first- and second-order distortions in the phase shift and a much reduced sensitivity to low-frequency mechanical vibration.