OPTICAL FIBER EXTRINSIC MICRO-CAVITY SCANNING MICROSCOPY

An extrinsic Fabry-Perot cavity in optical flber is used to achieve surface imaging at infrared wavelengths. The micro-cavity is realized by approaching a single mode flber with a numerical aperture NA to a sample and it is fed by a low-coherence source. The measurement of the re∞ected optical intensity provides a map of the sample re∞ectivity, whereas from the analysis of the re∞ected spectrum in the time/spatial domain, we disentangle the topography and contrast phase information, in the limit of nearly homogeneous sample with complex permittivity having Im(") ? Real("). The transverse resolution is not deflned by the numerical aperture NA of the flber and consequently by the conventional Rayleigh limit (about 0.6‚=NA), but it is a function of the transverse fleld behavior of the electromagnetic fleld inside the micro-cavity. Difierently, the resolution in the normal direction is limited mainly by the source bandwidth and demodulation algorithm. The system shows a compact and simple architecture. An analytical model for data interpretation is also introduced.

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