Spectral composition of low-coherence interferograms at high numerical apertures

Abstract

Interference signals in coherence scanning interferometry at high numerical apertures and narrow bandwidth illumination are spectrally broadened. This enables phase analysis within a spectral range much wider than the spectral distribution of the light emitted by the light source. Consequently, different surface features can be resolved depending on the wavelength used for phase analysis of the interference signals. In addition, the surface topography itself affects the spectral composition of interference signals in different ways. Signals related to tilted surfaces or step height structures show special spectral characteristics. Thus, spectral amplitude and phase analysis enables a better understanding of the underlying physical mechanisms and gives hints how to improve the measurement accuracy.

Resolution enhancement through nearfield-assistance in interference microscopy

“…The lower heigth value in the microsphere measurement can be attributed to the large influence of the evaluation wavelength on the phase evaluation result and the low-pass filtering transfer characteristic of the entire imaging system. In [10,12] investigations are shown which illustrate the direct relationship between the evaluation wavelength and the measured structure height.…”

“…Then topographies are calculated from the measurement data using envelope and phase evaluation [24]. It has been shown that the parameters of the phase evaluation are crucial when evaluating the measurement data [10,12].…”

Spatially Resolved Optical Characterization of Functional Materials Using Coherence Scanning Interferometry

“…One main application of the local spectroscopy technique is to be able to study different materials on the same sample and in the same field of view. With this in mind, we developed a sample consisting of four different materials with the surfaces roughly in the same plane [ 19,20 ] that can be measured locally using the proposed technique as well as with a classical spectrometer with a larger spot size.…”

“…Failure to reduce the angle of the illumination cone results in degraded spectral measurements as their amplitude is severely attenuated. [ 18,20 ] Because of the need to close down the AD, the lateral measurement spot size is increased to 0.85 μm in diameter. These experimental results demonstrate that depth‐resolved reflectance spectra of buried materials can be performed with interference microscopy.…”

Does interferometry work? A critical look at the foundations of interferometric surface topography measurement

“…These methods take advantage of the rate of change of interference phase with wavelength to measure a wide variety of objects, including high steps and rough textures. A known difficulty with these techniques is that the transfer characteristics of the optics are wavelength dependent [33,34]. Differences in the spatial frequency response with wavelength can result in large errors in the measured topography, particularly with steep slopes and sharp step-like features.…”