1. Articles from opticsinfobase.org

  2. 1177-1200 of 1217 « 1 2 ... 47 48 49 50 51 »
    1. Processing advantages of linear chirped fiber Bragg gratings in the time domain realization of optical frequency-domain reflectometry

      R. E. Saperstein, N. Alic, S. Zamek, K. Ikeda, B. Slutsky, Y. Fainman The inclusion of a linear chirped fiber Bragg grating for short pulse dispersion is shown to enhance the time domain realization of optical frequency-domain reflectometry. A low resolution demonstrator is constructed with single surface scans containing 140 resolvable spots. The system dynamic ... [Opt. Express 15, 15464-15479 (2007)]
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    2. High speed engine gas thermometry by Fourier-domain mode-locked laser absorption spectroscopy

      We present a novel method for low noise, high-speed, real-time spectroscopy to monitor molecular absorption spectra. The system is based on a rapidly swept, narrowband CW Fourier-domain mode-locked (FDML) laser source for spectral encoding in time and an optically time-multiplexed split-pulse data ... [Opt. Express 15, 15115-15128 (2007)]
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    3. Normalization detection scheme for high-speed optical frequency-domain imaging and reflectometry

      We introduce a new signal detection method that can effectively suppress the effect of relative intensity noise (RIN) in optical frequency-domain reflectometry or imaging (OFDR/OFDI) schemes to enhance the sensitivity and dynamic range. In this method, spectral interferogram signal is normalized digitally by a spectral reference signal that contains the real-time spectrum and the RIN information of the frequency-swept source. Unlike the conventional balanced detection method that suppresses only additive intensity noises, we found that our proposed scheme removes both the additive and convolutional contributions of the RINs in the final interferogram signals. Experimental demonstrations were performed using a ...
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    4. High speed in situ depth profiling of ultrafast micromachining

      We demonstrate real-time depth profiling of ultrafast micromachining of stainless steel at scan rates of 46 kHz. The broad bandwidth and high power of the light source allows for simultaneous machining and coaxial Fourier-domain interferometric imaging of the ablation surface with depth resolutions ... [Opt. Express 15, 14967-14972 (2007)]
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    5. Automatic retinal blood flow calculation using spectral domain optical coherence tomography

      Keywords (OCIS): (110.4500) Imaging systems : Optical coherence tomography (120.3890) Instrumentation, measurement, and metrology : Medical optics instrumentation (170.4580) Medical optics and biotechnology : Optical diagnostics for medicine Abstract Optical Doppler tomography (ODT) is a branch of optical coherence tomography (OCT) that can measure the speed of a blood flow by measuring the Doppler shift impinged on the probing sample light by the moving blood cells. However, the measured speed
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    6. In vivo three-dimensional spectral domain endoscopic optical coherence tomography using a microelectromechanical system mirror

      Woonggyu Jung, Daniel T. McCormick, Yeh-Chan Ahn, Ali Sepehr, Matt Brenner, Brian Wong, Norman C. Tien, Zhongping Chen A biopsy is a well-known medical test used to evaluate tissue abnormality. Biopsy specimens are invasively taken from part of a lesion and visualized by microscope after chemical treatment. However, diagnosis by means of biopsy is not only variable due to depth and location of specimen but may also ... [Opt. Lett. 32, 3239-3241 (2007)]
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    7. An assessment of the Wigner distribution method in Doppler OCT

      Analyzing the experimental data of the velocity distribution in a fluid flow using Doppler Optical Coherence Tomography (OCT), we compared the Wigner distribution method to the short-time Fourier transform method, the Hilbert-based phase-resolved method and the autocorrelation method. We conclude that the pseudo Wigner-distribution signal processing method is overall more precise than other often-used methods in Doppler OCT for the analysis of cross-sectional velocity distributions.
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    8. Digital holographic tomography based on spectral interferometry

      Digital holographic tomography based on spectral interferometry

      A digital holographic tomography system has been developed with the use of an inexpensive broadband light source and a fiber-based spectral interferometer. Multiple synthesized holograms (or object wave fields) of different wavelengths are obtained by transversely scanning a probe beam. The acquisition speed is improved compared with conventional wavelength-scanning digital holographic systems. The optical field of a volume around the object location is calculated by numerical diffraction from each synthesized hologram, and all such field volumes are numerically superposed to create the three-dimensional tomographic image. Experiments were performed to demonstrate the idea.

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    9. Simultaneous dual-band ultra-high resolution optical coherence tomography

      Simultaneous dual-band ultra-high resolution optical coherence tomography
      Ultra-high resolution optical coherence tomography (OCT) imaging is demonstrated simultaneously at 840 nm and 1230 nm central wavelength using an off-the-shelf turn-key supercontinuum light source. Spectral filtering of the light source emission results in a double peak spectrum with average powers exceeding 100 mW and bandwidths exceeding 200 nm for each wavelength band. A free-space OCT setup optimized to support both wavelengths in parallel is introduced. OCT imaging of biological tissue ex vivo and in vivo is demonstrated with axial resolutions measured to be < 2 μm and < 4 μm at 840 nm and 1230 nm, respectively. This measuring scheme is ...
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    10. High-speed imaging of human retina in vivo with swept-source optical coherence tomography

      We present the first demonstration of human retinal imaging in vivo using optical frequency domain imaging (OFDI) in the 800-nm range. With 460-μW incident power on the eye, the sensitivity is 91 dB at maximum and >85 dB over 2-mm depth range. The axial resolution is 13 μm in air. We acquired images of retina at 43,200 depth profiles per second and a continuous acquisition speed of 84 frames/s (512 A-lines per frame) could be maintained over more than 2 seconds.
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    11. Molecular imaging of endogenous and exogenous chromophores using ground state recovery pump-probe optical coherence tomography

      Molecular imaging of endogenous and exogenous chromophores using ground state recovery pump-probe optical coherence tomography
      We present a novel molecular imaging technique which combines the 3-D tomographic imaging capability of optical coherence tomography with the molecular sensitivity of pump-probe spectroscopy. This technique, based on transient absorption, is sensitive to any molecular chromophore. It is particularly promising for the many important biomarkers, such as hemoglobin, which are poor fluorophores and therefore difficult to image with current optical techniques without chemical labeling. Previous implementations of pump-probe optical coherence tomography have suffered from inefficient pump-probe schemes which hurt the sensitivity and applicability of the technique. Here we optimize the efficiency of the pump-probe approach by avoiding the steady-state ...
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    12. Transversal ultrahigh-resolution polarization-sensitive optical coherence tomography for strain mapping in materials

      Transversal ultrahigh-resolution polarization-sensitive optical coherence tomography for strain mapping in materials

      Optical coherence tomography (OCT) and its extension, polarization-sensitive (PS-)OCT, are techniques for contactless and non-destructive imaging of internal structures. In this work, we apply PS-OCT for material characterization. We use a transversal scanning, ultra-high resolution (UHR-)PS-OCT setup providing cross-sectional as well as in-plane information about the internal microstructure, the birefringence and the orientation of the optical axis within the material. We perform structural analysis and strain-mapping for different samples: we show the necessity of UHR imaging for a highly strained elastomer sample, and we discuss the effect of large birefringence on the PS-OCT images. Furthermore, we investigate high-aspect ...

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    13. Depth-resolved monitoring of glucose diffusion in tissues by using optical coherence tomography

      We demonstrate the capability of the optical coherence tomography (OCT) technique for depth-resolved monitoring and quantifying of glucose diffusion in fibrous tissues (sclera). The depth-resolved and average permeability coefficients of glucose were calculated. We found that the glucose diffusion rate is not uniform throughout the tissue and is increased from approximately 2.39±0.7310−6 cm/s at the epithelial side to 8.63±0.2710−6 cm/s close to the endothelial side of the sclera. Results demonstrated that the OCT technique is capable of depth-resolved monitoring and quantification of glucose diffusion in sclera with a ...
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    14. Supercontinuum generation system for optical coherence tomography based on tapered photonic crystal fibre

      We report smooth and broad continuum generation using a compact femtosecond Ti:Sapphire laser as a pump source and a tapered photonic crystal fibre as a nonlinear element. Spectral output is optimised for use in optical coherence tomography, providing a maximum longitudinal resolution of 1.5 µm in free space at 809 nm centre wavelength without use of additional spectral filtering.
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    15. 4D embryonic cardiography using gated optical coherence tomography

      4D embryonic cardiography using gated optical coherence tomography
      Simultaneous imaging of very early embryonic heart structure and function has technical limitations of spatial and temporal resolution. We have developed a gated technique using optical coherence tomography (OCT) that can rapidly image beating embryonic hearts in four-dimensions (4D), at high spatial resolution (10-15 μm), and with a depth penetration of 1.5 - 2.0 mm that is suitable for the study of early embryonic hearts. We acquired data from paced, excised, embryonic chicken and mouse hearts using gated sampling and employed image processing techniques to visualize the hearts in 4D and measure physiologic parameters such as cardiac volume, ejection ...
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    16. Automated detection of retinal layer structures on optical coherence tomography images

      Automated detection of retinal layer structures on optical coherence tomography images
      Segmentation of retinal layers from OCT images is fundamental to diagnose the progress of retinal diseases. In this study we show that the retinal layers can be automatically and/or interactively located with good accuracy with the aid of local coherence information of the retinal structure. OCT images are processed using the ideas of texture analysis by means of the structure tensor combined with complex diffusion filtering. Experimental results indicate that our proposed novel approach has good performance in speckle noise removal, enhancement and segmentation of the various cellular layers of the retina using the STRATUSOCTTM system.
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    17. Theoretical comparison of the sensitivity of molecular contrast optical coherence tomography techniques

      Theoretical comparison of the sensitivity of molecular contrast optical coherence tomography techniques
      Molecular contrast optical coherence tomography (MCOCT) is an extension of OCT in which contrast resulting from the interaction of light with a contrast agent, leads to the enhanced visualization of a specific morphology or biochemical process in a target specimen. In order to improve the sensitivity and specificity of MCOCT, several spectroscopic techniques have recently been introduced which depend upon coherent detection of scattered light which has been modified by interaction with the molecules of interest in a sample. These techniques include harmonic generation, coherent anti-Stokes Raman scattering, linear absorption, and several different forms of pump-probe spectroscopy. We have developed ...
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    18. En-face optical coherence tomography – a novel application of non-invasive imaging to art conservation

      En-face optical coherence tomography – a novel application of non-invasive imaging to art conservation
      Optical Coherence Tomography (OCT) is an optical interferometric technique developed mainly for in vivo imaging of the eye and biological tissues. In this paper, we demonstrate the potential of OCT for non-invasive examination of museum paintings. Two en-face scanning OCT systems operating at 850 nm and 1300 nm were used to produce B-scan and C-scan images at typical working distances of 2 cm. The 3D images produced by the OCT systems show not only the structure of the varnish layer but also the paint layers and underdrawings (preparatory drawings under the paint layers). The highest ever resolution and dynamic range ...
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    19. Task-based Optimization and Performance Assessment in Optical Coherence Imaging

      Task-based Optimization and Performance Assessment in Optical Coherence Imaging
      Optimization of an optical coherence imaging (OCI) system on the basis of task performance is a challenging undertaking. We present a mathematical framework based on task performance that uses statistical decision theory for the optimization and assessment of such a system. Specifically, we apply the framework to a relatively simple OCI system combined with a specimen model for a detection task and a resolution task. We consider three theoretical Gaussian sources of coherence lengths of 2, 20, and 40 µm. For each of these coherence lengths we establish a benchmark performance that specifies the smallest change in index of refraction ...
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    20. Characterization of dentin, enamel, and carious lesions by a polarization-sensitive optical coherence tomography system

      Enamel and dentin are the primary components of human teeth. Both of them have a strong polarization effect. We designed a polarization-sensitive optical coherence tomography (PSOCT) system to study the spatially resolved scattering and polarization phenomena of teeth. The system is constructed in free space to avoid the complexity of polarization control in fiber-based PSOCT. The structural features of enamel were evaluated in five human teeth that had no visible evidence of caries. The teeth were subsequently sectioned in mesial distal orientation and coronal orientation. Then the structural aspects of dentin were evaluated. OCT images were made of the mantel ...
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    21. Ultrahigh-resolution optical coherence tomography with a fiber laser source at 1 µm

      Ultrahigh-resolution optical coherence tomography with a fiber laser source at 1 µm
      We report a compact, high-power, fiber-based source for ultrahigh-resolution optical coherence tomography (OCT) near 1 µm. The practical source is based on a short-pulse, ytterbium-doped fiber laser and on generation of a continuum spectrum in a photonic crystal fiber. The broadband emission has an average power of 140 mW and offers an axial resolution of 2.1 µm in air (<1.6 µm in biological tissue). The generation of a broad bandwidth is robust and efficient. We demonstrate ultrahigh-resolution, time-domain OCT imaging of in vitro and in vivo biological tissues.
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    22. En-face scanning optical coherence tomography with ultra-high resolution for material investigation

      En-face scanning optical coherence tomography with ultra-high resolution for material investigation
      Optical coherence tomography (OCT) is an emerging technique for cross-sectional imaging, originally developed for biological structures. When OCT is employed for material investigation, high-resolution and short measurement times are required, and for many applications, only transversal (en-face) scans yield substantial information which cannot be obtained from cross-sectional images oriented perpendicularly to the sample surface alone. In this work, we combine transversal with ultra-high resolution OCT: a broadband femto-second laser is used as a light source in combination with acousto-optic modulators for heterodyne signal generation and detection. With our setup we are able to scan areas as large as 3 x ...
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    23. Real-time, ultrahigh-resolution, optical coherence tomography with an all-fiber, femtosecond fiber laser continuum at 1.5 μm

      Real-time, ultrahigh-resolution, optical coherence tomography with an all-fiber, femtosecond fiber laser continuum at 1.5 μm

      Real-time, ultrahigh-resolution optical coherence tomography (OCT) is demonstrated in the 1.4¿1.7-μm wavelength region with a stretched-pulse, passively mode-locked, Er-doped fiber laser and highly nonlinear fiber. The fiber laser generates 100-mW, linearly chirped pulses at a 51-MHz repetition rate. The pulses are compressed and then coupled into a normally dispersive highly nonlinear fiber to generate a low-noise supercontinuum with a 180-nm FWHM bandwidth and 38 mW of output power. This light source is stable, compact, and broadband, permitting high-speed, real-time, high-resolution OCT imaging. In vivo high-speed OCT imaging of human skin with ~5.5-μm resolution and 99-dB sensitivity ...

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    24. Miniature Endoscope for Simultaneous Optical Coherence Tomography and Laser-Induced Fluorescence Measurement

      We have designed a multimodality system that combines optical coherence tomography (OCT) and laser-induced fluorescence (LIF) in a 2.0-mm-diameter endoscopic package. OCT provides ~18-μm resolution cross-sectional structural information over a 6-mm field. LIF spectra are collected sequentially at submillimeter resolution across the same field and provide histochemical information about the tissue. We present the use of a rod prism to reduce the asymmetry in the OCT beam caused by a cylindrical window. The endoscope has been applied to investigate mouse colon cancer in vivo.
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    1177-1200 of 1217 « 1 2 ... 47 48 49 50 51 »
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