Fourier analysis of interferograms captured in white light interference microscopy is proposed for performing simultaneous local spectral and topographic measurements at high spatial resolution over a large field of view. The technique provides a wealth of key information on local sample properties. We describe the necessary processing and calibration involved to produce reflectivity maps of spatially extended samples. This enables precise and fast identification between different materials at a local scale of 1 µm. We also show that the recovered spectral information can be further used for improving topography measurements, particularly in the case of samples combining dielectric and conducting materials in which the complex refractive index can result in nanometric height errors.

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Interference microscopy is a non-destructive full-field imaging method, mainly used to measure the surface topography of different samples. In this work, two designs for improving the signal quality are described. The first consists of an original vertically orientated breadboard interferometer, in a Linnik configuration. The mechanical design of the arms allows the independent control and alignment of the coherence and the focal plane positions for optimizing fringe contrast. A low noise 16-bit camera is used to improve the sensitivity. The second interferometer is based on a Thorlabs tube system, with a Nikon Mirau Objective and a white LED, all controlled with IGOR Pro software or Labview, with the aim of being more compact, flexible and mobile. For both systems, an evaluation of the interferometric signal quality is performed, whereas the difference in lateral resolution by considering the 3D nature of the interferometric system, or only its 2D imaging abilities, is explored.

Despite the gain in resolution brought by microsphere (MS)-assisted microscopy, it has always faced several limitations, such as a limited field of view, surface defects, low contrast, and lack of manipulability. This Letter presents a new type of MS created at the tip of an optical fiber, which we call a fiber microsphere (fMS). The fMS is made from a single-mode or coreless fiber, molten and stretched, ensuring high homogeneity and a sphere diameter smaller than the fiber itself. In addition, the connection between the fMS and the fiber makes scanning the sample a simple task, offering a solution to the difficulties of handling. The fabrication procedure of the fMS and the optical system used in the study are detailed. Our measurements show a clear superiority of the fMS over the soda-lime MS in resolving power and imaging performance.

Herein, some of the work in adapting white light interference microscopy to perform local spectroscopy for measuring the optical properties of microscopic structures is reviewed. Theoretical and experimental results are shown in which Fourier transform processing of the polychromatic fringe signal combined with careful calibration of the optical system is used to make measurements of local reflectance spectra. This approach captures the spectral information within the entire field of view in a single scan, allowing rapid spectral mapping of spatially extended surfaces. Results are shown of local reflectance spectra measured on different materials and buried under transparent layers with a lateral spot size of between 0.5 μm and several micrometer over a field of view up to 650 × 650 μm. The technique is extended to the measurement of local refractive index and thickness of transparent layers as well as to the size determination of small spherical beads buried in transparent and scattering layers with a priori information. The significance of the work is the potential for local materials characterization in complex, hybrid, and functional materials and even disease detection through the study of living cells.