In this paper, we present a disturbance compensation technique to improve the performance of interferometric imaging for extremely large ground-based telescopes, e.g., the Large Binocular Telescope (LBT), which serves...
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In this paper, we present a disturbance compensation technique to improve the performance of interferometric imaging for extremely large ground-based telescopes, e.g., the Large Binocular Telescope (LBT), which serves as the application example in this contribution. The most significant disturbance sources at ground-based telescopes are wind-induced mechanical vibrations in the range of 8-60 Hz. Traditionally, their optical effect is eliminated by feedback systems, such as the adaptive optics control loop combined with a fringe tracking system within the interferometric instrument. In this paper, accelerometers are used to measure the vibrations. These measurements are used to estimate the motion of the mirrors, i.e., tip, tilt and piston, with a dynamic estimator. Additional delay compensation methods are presented to cancel sensor network delays and actuator input delays, improving the estimation result even more, particularly at higher frequencies. Because various instruments benefit from the implementation of telescope vibration mitigation, the estimator is implemented as a separate, independent software on the telescope, publishing the estimated values via multicast on the telescope's ethernet. Every client capable of using and correcting the estimated disturbances can subscribe and use these values in a feedforward for its compensation device, e.g., the deformable mirror, the piston mirror of LINC-NIRVANA, or the fast path length corrector of the Large Binocular Telescope Interferometer. This easy-to-use approach eventually leveraged the presented technology for interferometric use at the LBT and now significantly improves the sky coverage, performance, and operational robustness of interferometric imaging on a regular basis. (C) 2017 Optical Society of America
We propose and experimentally demonstrate a scheme of a coherent Brillouin time domain analysis (BOTDA) system without any trace averaging. Assisted by a commercial integrated coherent receiver with a local oscillator...
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We propose and experimentally demonstrate a scheme of a coherent Brillouin time domain analysis (BOTDA) system without any trace averaging. Assisted by a commercial integrated coherent receiver with a local oscillator generated through single sideband modulation from the same laser source, the Brillouin signals carried on a stable intermediate frequency (IF) are extracted by electrical/digital filters and then recovered to baseband by digital signal processing. This increases the signal-to-noise ratio and avoids the need of trace averaging and enables real-time signal acquisition. To eliminate the Brillouin gain fluctuation, two adjacent Brillouin time-domain traces stimulated by two sequential orthogonal pump pulses are recovered after the IF signals are detected in a real-time manner. Based on this configuration, a spatial resolution of 4 m and Brillouin frequency shift uncertainty of 1.473 MHz are realized in distributed temperature sensing over 40.63 km range. With the nonlocal means algorithm and distributed Raman amplification integrated into the system, the BFS uncertainty is enhanced to 0.843 MHz and better spatial resolution of 2 m over the same sensing fiber is achieved.
In this presentation, we will highlight our recent advances in translating biophotonic approaches with special focus on linear and non-linear Raman spectroscopy towards routine clinical applications with focus on infe...
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ISBN:
(纸本)9781943580279
In this presentation, we will highlight our recent advances in translating biophotonic approaches with special focus on linear and non-linear Raman spectroscopy towards routine clinical applications with focus on infectious diseases and cancer.
We demonstrate digital holographic microscopy that, while being based on phase-shifting interferometry, is capable of single-shot measurements. A two-dimensional (2-D) diffraction grating placed in a Fourier plane of ...
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We demonstrate digital holographic microscopy that, while being based on phase-shifting interferometry, is capable of single-shot measurements. A two-dimensional (2-D) diffraction grating placed in a Fourier plane of a standard in-line holographic phase microscope generates multiple copies of a sample image on a camera sensor. The identical image copies are spatially separated with different overall phase shifts according to the diffraction orders. The overall phase shifts are adjusted by controlling the lateral position of the grating. These phase shifts are then set to be multiples of pi/2. Interferograms composed of four image copies combined with a parallel reference beam are acquired in a single shot. The interferograms are processed through a phase-shifting algorithm to produce a single complex image. By taking advantage of the higher sampling capacity of the in-line holography, we can increase the imaging information density by a factor of 3 without compromising the imaging acquisition speed. (C) 2016 Optical Society of America
We demonstrate speckle-suppressed full-field imaging through a scattering medium using incoherent supercontinuum (SC) illumination. The patterns in images obtained using SC illumination were found to be more easily id...
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We demonstrate speckle-suppressed full-field imaging through a scattering medium using incoherent supercontinuum (SC) illumination. The patterns in images obtained using SC illumination were found to be more easily identifiable than those in images acquired using coherent direct laser illumination due to the speckle suppression. Even when the optical depth reached 12.3, the patterns remained identifiable. As one of the potential applications, we also demonstrated the imaging for a high-pressure diesel spray using SC illumination. (C) 2016 Optical Society of America
We investigate the detection performance of transverse and longitudinal planes for various signal sizes (i.e., 1 mm to 8 mm diameter spheres) in cone beam computed tomography (CBCT) images. CBCT images are generated b...
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We investigate the detection performance of transverse and longitudinal planes for various signal sizes (i.e., 1 mm to 8 mm diameter spheres) in cone beam computed tomography (CBCT) images. CBCT images are generated by computer simulation and images are reconstructed using an FDK algorithm. For each slice direction and signal size, a human observer study is conducted with a signal-known-exactly/background-known-exactly (SKE/BKE) binary detection task. The detection performance of human observers is compared with that of a channelized Hotelling observer (CHO). The detection performance of an ideal linear observer is also calculated using a CHO with Laguerre-Gauss (LG) channels. The detectability of high contrast small signals (i.e., up to 4-mm-diameter spheres) is higher in the longitudinal plane than the transverse plane. It is also shown that CHO performance correlates well with human observer performance in both transverse and longitudinal plane images. (C) 2016 Optical Society of America
Poor motion estimation and subsequent registration are detrimental to super-resolution (SR). In this paper, we present a camera sampling method for achieving SR in concentric circular trajectory sampling (CCTS). Using...
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Poor motion estimation and subsequent registration are detrimental to super-resolution (SR). In this paper, we present a camera sampling method for achieving SR in concentric circular trajectory sampling (CCTS). Using this method, we can precisely control regular radial and angular shifts in CCTS. SR techniques can be subsequently applied ring by ring in radial and angular dimensions. Not only does the proposed camera sampling method eliminate the transient behavior and increases the sampling speed in CCTS, it also preserves the SR accuracy. Our experimental results demonstrate that our approach can accurately discriminate SR pixels from blurry images. (C) 2016 Optical Society of America
Laser ultrasonics is a technique where lasers are employed to generate and detect ultrasound. A data collection method (full matrix capture) and a post processing imaging algorithm, the total focusing method, both dev...
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Laser ultrasonics is a technique where lasers are employed to generate and detect ultrasound. A data collection method (full matrix capture) and a post processing imaging algorithm, the total focusing method, both developed for ultrasonic arrays, are modified and used in order to enhance the capabilities of laser ultrasonics for nondestructive testing by improving defect detectability and increasing spatial resolution. In this way, a laser induced ultrasonic phased array is synthesized. A model is developed and compared with experimental results from aluminum samples with side drilled holes and slots at depths of 5 - 20 mm from the surface. (C) 2016 Optical Society of America
The accuracy of strain measurement using a common optical extensometer with two-dimensional (2D) digital image correlation (DIC) is not sufficient for experimental applications due to the effect of out-of-plane motion...
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The accuracy of strain measurement using a common optical extensometer with two-dimensional (2D) digital image correlation (DIC) is not sufficient for experimental applications due to the effect of out-of-plane motion. Although three-dimensional (3D) DIC can measure all three components of displacement without introducing in-plane displacement errors, 3D-DIC requires the stringent synchronization between two digital cameras and requires complicated system calibration of binocular stereovision, which makes the measurement rather inconvenient. To solve the problems described above, this paper proposes a self-calibration single-lens 3D video extensometer for non-contact, non-destructive and high-accuracy strain measurement. In the established video extensometer, a single-lens 3D imaging system with a prism and two mirrors is constructed to acquire stereo images of the test sample surface, so the problems of synchronization and out-of-plane displacement can be solved easily. Moreover, a speckle-based self-calibration method which calibrates the single-lens stereo system using the reference speckle image of the specimen instead of the calibration targets is proposed, which will make the system more convenient to be used without complicated calibration. Furthermore, an efficient and robust inverse compositional Gauss-Newton algorithm combined with a robust stereo matching stage is employed to achieve high-accuracy and real-time subset-based stereo matching. Tensile tests of an Alalloy specimen were performed to demonstrate the feasibility and effectiveness of the proposed self-calibration single-lens 3D video extensometer. (C) 2016 Optical Society of America
For the first time, proposed and demonstrated is a simultaneous dual optical band coded access optical sensor (CAOS) camera design suited for extreme contrast multispectral bright target scenarios. Deploying a digital...
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For the first time, proposed and demonstrated is a simultaneous dual optical band coded access optical sensor (CAOS) camera design suited for extreme contrast multispectral bright target scenarios. Deploying a digital micromirror devices (DMDs)-based time-frequency agile pixels CAOS-mode within a two point detector spatially and spectrally isolating framework, this imager simultaneously and independently detects pixel selective image information for two different broad spectral bands that further undergo independent spectral image data extraction via finer-tuned wavelength filtering using all-optical or CAOSmode electronic filters. A proof-of-concept visible-near infrared band CAOS imager is successfully demonstrated using a target scene containing LEDs and engaging narrowband optical filters. In addition, using the CAOS-mode, demonstrated is the RF domain simultaneous color content monitoring of a white light LED image pixel. Also proposed is the use of a higher bit count analog-to-digital converter (ADC) with both range and sampling duration parameter control along with a larger data set electronic DSP to extract higher DSP gain and realize additional noise suppression. Using a 16-bit ADC and 2,097,152 point fast Fourier transform (FFT) digital signal processing (DSP) for a 633 nm laser engaged test target scene that is subject to nearly 7 decades (10(7)) of gradual optical attenuation, the experimental camera demonstrates an agile pixel extreme dynamic range of 136 dB, which is a 56 dB improvement over the previous CAOS-imaging demonstrations. (C) 2016 Optical Society of America
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