We demonstrate the ability of multiple forms of optical coherence tomography (OCT) in the frequency domain to quantitatively size scatterers. Combined with a variety of distinct phantoms, we gain insight into the measurement uncertainties associated with using scattering spectra to size scatterers. We size spherical scatterers on a surface using swept-source OCT with an analysis based on a simple slab-mode resonance model. Automating this technique, a two-dimensional (2-D) image is created by raster scanning across a surface phantom designed to have a distinct size transition to demonstrate accuracy and repeatability. We also investigate the potential of a novel sphere-nanotube structure as a quantitative calibration artifact for use in comparing measured intensity and phase scattering spectra directly to Mie theory predictions. In another experiment, we demonstrate tissue-relevant sizing of scatterers as small as 5 µm on a surface by use of a Fourier domain OCT system with 280 nm of bandwidth from a supercontinuum source. We perform an uncertainty analysis for our high-resolution sizing system, estimating a sizing error of 9% for measurements of spheres with a diameter of 15 µm. With appropriate modifications, our uncertainty analysis has general applicability to other sizing techniques utilizing scattering spectra.
We present spectroscopic swept-source optical coherence tomography (OCT) measurements of the phase-dispersion of
cell samples. We have previously demonstrated that the phase of the scattered field is, in general, independent of the
intensity, and both must be measured for a complete characterization of the sample. In this paper, we show that, in
addition to providing a measurement of the size of the cell nuclei, the phase spectrum provides a very sensitive
indication of the separations between the cells. Epithelial cancers are characterized by many factors, including enlarged
nuclei and a significant loss in the architectural orientation of the cells. Therefore, an <i>in vivo</i> diagnostic tool that
analyzes multiple properties of the sample instead of focusing on cellular nuclei sizes alone could provide a better
assessment of tissue health. We show that the phase spectrum of the scattered light appears to be more sensitive to cell
spacing than the intensity spectrum. It is possible to determine simultaneously the cell nuclei sizes from the intensity
spectrum and the nuclei spacing from the phase spectrum. We measure cell monolayer samples with high and low cell
density and compare measured results with histograms of the cell separations calculated from microscope images of the
samples. We show qualitative agreement between the predicted histograms and the interferometric results.
Using phase-dispersion spectra measured with optical coherence tomography (OCT) in the frequency domain, we
demonstrated the quantitative sizing of multiple spherical scatterers on a surface. We modeled the light scattering as a
slab-mode resonance and determined the size of the scatterers from a Fourier transform of the measured phasedispersion
spectra. Using a swept-source OCT system, we mapped the detected size of the scatters to the intensity of a
two-dimensional surface image. The image was formed by raster-scanning a collimated beam of 200 μm diameter
across a sample with distinct size domains. The image shows a clear distinction between deposited polystyrene
microspheres of 26 and 15 μm average sizes. In a separate experiment, we demonstrated tissue-relevant sizing of
scatters as small as 5 μm with a Fourier domain OCT system that utilized 280 nm of bandwidth from a super-continuum
source. Our previous studies have demonstrated that the light scattered from a single sphere is, in general, nonminimum-
phase; therefore, phase spectra can provide unique information about scattered light not available from
intensity spectra alone. Also, measurements of phase spectra do not require background normalization to correct for the
spectral shape of light sources or the spectral absorption of specimens. The results we report here continue our efforts
towards combining intensity and phase spectra to enable improved quantitative analysis of complex tissue structures.
We demonstrate a novel technique to determine the size of Mie scatterers with high sensitivity. Our technique is based on spectral domain optical coherence tomography measurements of the dispersion that is induced by the scattering process. We use both Mie scattering theory and dispersion measurements of phantoms to show that the scattering dispersion is very sensitive to small changes in the size and/or refractive index of the scatterer.
We review wavelength accuracy and calibration issues for wavelength division multiplexed (WDM) optical fiber communication and describe our work on wavelength calibration references. We have developed wavelength references for National Institute of Standards and Technology (NIST) internal calibration and transfer standards to help industry calibrate their instrumentation. The transfer standards are NIST Standard Reference Materials that utilize the absorption lines of acetylene and hydrogen cyanide in the 1500 nm region. Two higher accuracy references for NIST internal use are based on laser stabilization to absorption lines of rubidium (at 1560 nm) and methane (at 1314 nm). We are developing calibration references for the WDM L-band (approximately 1565 - 1625 nm) and are investigating references for the 1300 - 1400 nm region.
We report both experimental and theoretical results for a physical implementation of a bipolar encoding scheme suitable for fiber optic networks. The power spectrum of an erbium-doped superfluorescent fiber source is encoded, the bipolar correlations of the codes are verified and rejection of multiple-access interference is demonstrated in a fiber- based testbed. Simulations of the correlation process identify key optical parameters and physical characteristics important to the design of future systems.
Zirconium dioxide films were spin cast onto silica or silicon substrates from an aqueous solution comprised of the precursor metal nitrate and an organic complexant such as glycine. The hydrated films so derived consist of an amorphous organic phase in which the metal cations and nitrate anions are homogeneously dispersed. Heating to temperatures above 200 degrees C leads to film dehydration followed by an auto-catalyzed oxidation reaction whereby the bound nitrate oxidizes the organic matrix leaving behind an intact stoichiometric and crystalline metal oxide film. Films are characterized using AFM, XRD, and optical methods. Transformation processes in these films have been studied in detail by means of spectroscopic ellipsometry and laser induced fluorescence from films doped with a suitable rare earth probe ion such as Sm<SUP>+3</SUP>. In the latter case, the measured fluorescence emission spectra are used to identify the hydrated, dehydrated, amorphous and crystalline metal oxide phases which evolve during processing. These transformations also have been induced upon visible CW laser irradiation at fluences in excess of 1 MW/cm<SUP>2</SUP>. Under these conditions, the film dehydrates and compacts within the footprint of the incident laser beam rendering this region of the film water insoluble. Post irradiation washing of the film with water removes all vestiges of the film outside of the beam footprint suggesting a possible use of this technique for lithography applications. Films subjected to laser irradiation and post irradiation heating have been characterized with respect to thickness, phase composition, crystallite size and optical constants.
Microscopy using vacuum ultraviolet and soft x-ray radiation offers high resolution, high contrast, and chemical sensitivity. Holography and contact printing are unique in their potential to achieve wavelength-limited resolution because they eliminate optical elements and their imperfections. Both methods, however, lack magnification and require high resolution films and methods to recover images. We present our results on source development and film characterization.