Quantitative phase spectroscopy is presented as a novel method of measuring the wavelength-dependent refractive index of microscopic volumes. Light from a broadband source is filtered to an ~5 nm bandwidth and rapidly tuned across the visible spectrum in 1 nm increments by an acousto-optic tunable filter (AOTF). Quantitative phase images of semitransparent samples are recovered at each wavelength using off-axis interferometry and are processed to recover relative and absolute dispersion measurements. We demonstrate the utility of this approach by (i) spectrally averaging phase images to reduce coherent noise, (ii) measuring absorptive and dispersive features in microspheres, and (iii) quantifying bulk hemoglobin concentrations by absolute refractive index measurements. Considerations of using low coherence illumination and the extension of spectral techniques in quantitative phase measurements are discussed.

Background & Aims-Patients with Barrett's esophagus (BE) show increased risk for developing esophageal adenocarcinoma and are routinely examined using upper endoscopy with biopsy to search for neoplastic changes. Angle-resolved low coherence interferometry (a/LCI) uses in vivo depth-resolved nuclear morphology measurements to detect dysplasia. We assessed the clinical utility of a/LCI in the endoscopic surveillance of BE patients.

We present a phase-shifting interferometric technique for imaging live biological cells in growth media, while optimizing spatial resolution and enabling potential real-time measurement capabilities. The technique uses slightly-off-axis interferometry which requires less detector bandwidth than traditional off-axis interferometry and fewer measurements than traditional on-axis interferometry. Experimental and theoretical comparisons between the proposed method and these traditional interferometric approaches are given. The method is experimentally demonstrated via phase microscopy of live human skin cancer cells.

An all-fused-silica pressure sensor fabricated directly onto a fiber tip of 125 microm diameter is described. Simple fabrication steps include only cleaving and fusion splicing. Because no chemical processes are involved, the fabrication is easy, safe, and cost effective. Issues in sensor design and loss analysis are discussed. The sensor has been tested for static pressure response, showing a sensitivity of 2.2 nm/psi, a resolution of 0.01 psi (68.9 Pa), a hysteresis of 0.025%, and capability of operation at temperatures up to 600 deegrees C. This miniature sensor may be suitable for medical diagnostics, environmental monitoring, and other industrial applications.

Articles you may be interested inThe structural, morphological, defect properties, and OFF state leakage current mechanism of mixed As-Sb type-II staggered gap GaAs-like and InAs-like interface heterostructure tunnel field effect transistors (TFETs) grown on InP substrates using linearly graded In x Al 1-x As buffer by molecular beam epitaxy are investigated and compared. Symmetric relaxation of >90% and >75% in the two orthogonal h110i directions with minimal lattice tilt was observed for the terminal GaAs 0.35 Sb 0.65 and In 0.7 Ga 0.3 As active layers of GaAs-like and InAs-like interface TFET structures, respectively, indicating that nearly equal numbers of a and b dislocations were formed during the relaxation process. Atomic force microscopy reveals extremely ordered crosshatch morphology and low root mean square roughness of $3.17 nm for the InAs-like interface TFET structure compared to the GaAs-like interface TFET structure of $4.46 nm at the same degree of lattice mismatch with respect to the InP substrates. The GaAs-like interface exhibited higher dislocation density, as observed by cross-sectional transmission electron microscopy, resulting in the elongation of reciprocal lattice point of In 0.7 Ga 0.3 As channel and drain layers in the reciprocal space maps, while the InAs-like interface creates a defect-free interface for the pseudomorphic growth of the In 0.7 Ga 0.3 As channel and drain layers with minimal elongation along the Dx direction. The impact of the structural differences between the two interface types on metamorphic TFET devices was demonstrated by comparing p þ -i-n þ leakage current of identical TFET devices that were fabricated using GaAs-like and InAs-like interface TFET structures. Higher OFF state leakage current dominated by band-to-band tunneling process due to higher degree of defects and dislocations was observed in GaAs-like interface compared to InAs-like interface where type-II staggered band alignment was well maintained. Significantly lower OFF state leakage current dominated by the field enhanced Shockley-Read-Hall generation-recombination process at different temperatures was observed in InAs-like TFET structure. The fixed positive charge at the source/channel heterointerface influences the band lineup substantially with charge density greater than 1 Â 10 12 /cm 2 and the band alignment is converted from staggered gap to broken gap at $6 Â 10 12 /cm 2 . Clearly, InAs-like interface TFET structure exhibited 4Â lower OFF state leakage current, which is attributed primarily to the impact of the layer roughness, defect properties on the carrier recombination rate, suggesting great promise for metamorphic TFET devices for high-performance, and ultra-low power applications. V C 2012 American Institute of Physics.

Abstract. We present a novel Fourier-domain angle-resolved low-coherence interferometry (a /LCI) fiber probe designed for in vivo clinical application in gastrointestinal endoscopy. The a/LCI technique measures the depthresolved angular scattering distribution to determine the size distribution and optical density of cell nuclei for assessing the health of epithelial tissues. Clinical application is enabled by an endoscopic fiber-optic probe that employs a 2.3-m-long coherent fiber bundle and is compatible with the standard 2.8-mm-diam biopsy channel of a gastroscope. The probe allows for real-time data acquisition by collecting the scattering from multiple angles in parallel, enabled by the Fourier domain approach. The performance of the probe is characterized through measurement of critical parameters. The depth-resolved sizing capability of the system is demonstrated using single-and double-layer microsphere phantoms with subwavelength sizing precision and accuracy achieved. Initial results from a clinical feasibility test are also presented to show in vivo application in the human esophagus. C 2011 Society of Photo-Optical Instrumentation Engineers (SPIE).

We present a fiber-optic temperature sensor with a single-crystal sapphire fiber as the light guide and a sapphire wafer as the sensing element. Temperature is determined by measurement of the thermal dependence of the wafer's optical thickness by use of white-light interferometry. We applied digital signal processing techniques to analyze the sensor's spectrum. A prototype sensor was tested to 1600 degrees C and demonstrated excellent reproducibility. An accuracy of +/- 0.2% full scale was obtained. The sensor is simple, small, and flexible, with potential advantages of batch fabrication and easy calibration.

We introduce a new interferometric setup for single-exposure wide-field holographic phase imaging of highly dynamic biological samples. In this setup, the interferometric signal originates from a specially designed reflective interferometric chamber (InCh), creating an off-axis interferogram on the output plane of the system. The setup only requires the InCh and a simple reflection-mode two lens imaging system, without the need for additional optical elements such as gratings in the beam path. In addition, due to the close-to-common-path geometry of the setup, phase noise is greatly reduced. We experimentally compare the inherent phase stability of the system in ambient conditions to that of a conventional interferometer. We also demonstrate use of this system for wide-field quantitative phase imaging of two different highly dynamic, optically transparent biological samples: beating myocardial cells and moving unicellular microorganisms.