A miniature fiber optic spectrometer enclosed within a semipermeable (dialysis) membrane is proposed for in vivo interstitial sensing applications. The semipermeable membrane acts as a molecular filter, allowing only small molecules to pass through to the sampling volume. This filtering, in principle, should enable continuous in vivo drug sensing, removing the necessity for complex microdialysis systems. We use a biological phantom to examine the reliable detection of a fluorescence signal from small dye molecules in the presence of large fluorophores and scatterers. We find that spectral artefacts arising from scatterers and large fluorophores are substantially suppressed, simplifying the spectral analysis. In addition, the measured sampling rate of 157 s is superior to existing in vivo tissue assaying techniques such as microdialysis, which can take tens of minutes.
We report a new approach in optical coherence tomography (OCT) termed full-field Fourier-domain OCT (3F-OCT). A three-dimensional image of a sample is obtained by digital reconstruction of a three-dimensional data cube, acquired using a Fourier holography recording system illuminated with a swept-source. This paper presents theoretical and experimental study of the signal-to-noise ratio of the full-field approach versus serial image acquisition approach, represented by 3F-OCT and "flying-spot" OCT systems, respectively.
Full-field Fourier-domain optical coherence tomography (3F-OCT) is a full-field version of spectraldomain/swept-source optical coherence tomography. A set of two-dimensional Fourier holograms is recorded at discrete wavenumbers spanning the swept-source tuning range. The resultant three-dimensional data cube contains comprehensive information on the three-dimensional morphological layout of the sample that can be reconstructed in software via three-dimensional discrete Fourier-transform. This method of recording of the OCT signal confers signal-to-noise ratio improvement in comparison with "flying-spot" time-domain OCT. The spatial resolution of the 3F-OCT reconstructed image, however, is degraded due to the presence of a phase cross-term, whose origin and effects are addressed in this paper. We present theoretical and experimental study of imaging performance of 3F-OCT, with particular emphasis on elimination of the deleterious effects of the phase cross-term.
Silica glass can be poled either thermally or with UV exposure during application of a strong electric field. Such treatment allows electret formation. So normally isotropic glass can become anisotropic via formation of a frozen-in field. This produces non-zero second-order nonlinearity in glass. After such poling treatment a change in the third- order nonlinearity has been observed. In this paper we examine if modification of the third-order nonlinearity is real or some artifact. To do this the DC third-order nonlinearity was measured before poling, after poling and then after erasure of the second-order nonlinearity. It was found that modification of the third-order nonlinearity remains after erasure of the frozen-in field. The reason for modification of the third-order nonlinearity is still not understood. It may be due to some kind of structural modification of the glass. It is known that impurity ionic species are moved through the glass during poling. This movement of ions under the high field may be sufficient to modify the glass structure. From our results, it is clear that the second-order nonlinearity is predominantly caused by formation of a frozen-in field. The increase of the third-order nonlinearity is independent of existence of a frozen-in field after poling.