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Applied Optics

Vyacheslav A Trofimov, Svetlana A Varentsova
We discuss an effective method for detecting and identifying drugs using a high-noise terahertz (THz) signal. We add a noisy THz signal obtained in real conditions to the THz signal transmitted through a sample with the illicit drug methamphetamine. The insufficiency of the standard THz time-domain spectroscopy method is demonstrated, showing that this method detects the spectral features of neutral substances and explosives in a noisy THz signal. The method discussed is based upon time-dependent integral correlation criteria calculated using spectral dynamics of the medium response...
November 20, 2016: Applied Optics
Cheng-Kai Liu, Andy Ying-Guey Fuh, Ko-Ting Cheng
The single-cell-gap transflective liquid crystal display (TR-LCD) based on periodic distribution of surface anchoring energy (SAE) of periodical nano-grooved structures is reported in this study. Different SAEs of planar-aligned nematic LC cells are associated with the threshold and operation voltages of the adopted LCs. Thus, according to the transmittance versus applied voltage curves, the regions with strong and weak SAEs in LC cells can be the transmission and reflection regions of a TR-LCD, respectively...
November 20, 2016: Applied Optics
Dmitry V Petrov
In the present work, a multipass optical system intended for increasing the sensitivity of a Raman gas spectrometer based on the 90° geometry of scattered light collection is described. The system is characterized by an adjustment stability and an increased number of laser beams that pass through a small scattering volume, thus allowing the intensities of Raman signals from components of the gas medium in this volume to be increased. It is demonstrated that the application of this multipass optical system allows the sensitivity of the Raman gas spectrometer to be increased practically by 20 times (to several ppm for the 30-s registration time)...
November 20, 2016: Applied Optics
Alan Z Liu, Yafang Guo
Na lidar can measure vertical wind and temperature at high temporal and vertical resolutions, enough to resolve gravity wave perturbations. Heat flux due to dissipating gravity waves is an important quantity that can be derived from such perturbations. When lidar signals are high, a photomultiplier tube (PMT) used to count incoming photons may suffer from the saturation effect, and its output count is not linearly related to incoming photon counts. Corrections to this effect can be measured in a laboratory setting but may have large errors at high count rates...
November 20, 2016: Applied Optics
Carlos Manuel Ortiz-Lima, Alberto Cordero-Dávila, Jorge González-García
Small rigid petal tools, driven by a traditional polishing machine, were used to parabolize 20 mirrors 14 cm in diameter and 192 cm of curvature radius. Small rigid circular tools (SCTs), driven manually, were used to parabolize another 20 identical surfaces. A Ronchi test with a square grid was used to evaluate the performance of both techniques. If small rigid petal tools are used, the surface quality, the reproducibility in the production process, and the time spent required to generate the surfaces are markedly better than using SCTs...
November 20, 2016: Applied Optics
Lun Jiang, Na Li, Li-Zhong Zhang, Chao Wang, Yan An, Yuan Hu
We assessed the problem of low mixing efficiency caused by unstable signal polarization because of a moving reflector in a laser communication terminal with a periscopic scanner. A real-time polarization compensation method based on rotating waveplates is presented, which keeps the receiving signal light polarization at 45° linear polarized and improves system mixing efficiency. A geometric model of the laser communication terminal was first established, its polarization transmission characteristics were analyzed by three-dimensional polarization tracks, and a system polarization transmission matrix was calculated...
November 20, 2016: Applied Optics
Hoover Rueda, Henry Arguello, Gonzalo R Arce
Compressive spectral imaging systems can reliably capture multispectral data using far fewer measurements than traditional scanning techniques. In this paper, a thin-film patterned filter array-based compressive spectral imager is demonstrated, including its optical design and implementation. The use of a patterned filter array entails a single-step three-dimensional spatial-spectral coding on the input data cube, which provides higher flexibility on the selection of voxels being multiplexed on the sensor. The patterned filter array is designed and fabricated with micrometer pitch size thin films, referred to as pixelated filters, with three different wavelengths...
November 20, 2016: Applied Optics
Q Li, M Chambonneau, M Chanal, D Grojo
Laser-induced permanent modification inside silicon has been recently demonstrated by using tightly focused nanosecond sources at a 1550 nm wavelength. We have developed a quantitative-phase microscope operating in the near-infrared domain to characterize the laser-induced modifications deep into silicon. By varying the number of applied laser pulses and the energy, we observe porous and densified regions in the focal region. The observed changes are associated with refractive index variations |Δn| exceeding 10<sup>-3</sup>, enough to envision the laser writing of optical functionalities inside silicon...
November 20, 2016: Applied Optics
Roberto Lera, Francisco Valle-Brozas, Salvador Torres-Peiró, Alexandro Ruiz-de-la-Cruz, Miguel Galán, Pablo Bellido, Michael Seimetz, José María Benlloch, Luis Roso
A design of a diode side-pumped Nd:YAG laser module and simulations of the gain distribution inside the active medium are presented in this paper. The code is based on a nonsequential ray-tracing Monte Carlo method for the light generated by the laser diodes. The fluorescence image of the active medium was analyzed in order to compare it with the simulations, which were found to be in good agreement with experimental data. The laser was tested in QCW mode and provided a maximum average power of 220 W while maintaining constant energy per pulse in the 100-1000 Hz range...
November 20, 2016: Applied Optics
Yatong An, Tyler Bell, Beiwen Li, Jing Xu, Song Zhang
Structured light system calibration often requires the usage of a calibration target with a similar size as the field of view (FOV), which brings challenges to a large-range structured light system calibration since fabricating large calibration targets is difficult and expensive. This paper presents a large-range system calibration method that does not need a large calibration target. The proposed method includes two stages: (1) accurately calibrate intrinsics (i.e., focal lengths and principle points) at a near range where both the camera and projector are out of focus, and (2) calibrate the extrinsic parameters (translation and rotation) from camera to projector with the assistance of a low-accuracy, large-range three-dimensional (3D) sensor (e...
November 20, 2016: Applied Optics
Charles Pichette, Andrea Giudice, Simon Thibault, Yves Bérubé-Lauzière
Single-photon avalanche diodes (SPADs) achieving high timing resolution (≈20-50  ps) developed for time-correlated single-photon counting (TCSPC) generally have very small photosensitive areas (25-100 μm in diameter). This limits the achievable photon counting rate and signal-to-noise ratio and may lead to long counting times. This is detrimental in applications requiring several measurements, such as fluorescence lifetime imaging (FLIM) microscopy, which requires scanning, and time-domain diffuse optical tomography (TD-DOT)...
November 20, 2016: Applied Optics
Mahmudunnabi Basunia, Partha P Banerjee, Ujitha Abeywickrema, Ting-Chung Poon, Hongbo Zhang
Propagation of optical fields is governed by the Helmholtz equation or the paraxial wave equation. Transport of intensity is a noninterferometric method to find the phase of an object by recording optical intensities at different distances of propagation. The transport of intensity equation results from the imaginary part of the complex paraxial wave equation and is equivalent to the principle of conservation of energy. The real part of the paraxial wave equation yields the Eikonal equation in the presence of diffraction...
November 20, 2016: Applied Optics
Prateep Phatharacorn, Surasak Chiangga, Preecha Yupapin
The whispering gallery mode (WGM) is generated by light propagating within a nonlinear micro-ring resonator, which is modeled and made by an InGaAsP/InP material, and called a Panda ring resonator. An imaging probe can also be formed by the micro-conjugate mirror function for the appropriate Panda ring parameter control. The 3D WGM probe can be generated and used for a 3D sensor head and imaging probe. The analytical details and simulation results are given, in which the simulation results are obtained by using the MATLAB and Optiwave programs...
November 20, 2016: Applied Optics
Weiqing Gao, Qiang Xu, Xue Li, Wei Zhang, Jigang Hu, Yuan Li, Xiangdong Chen, Zijun Yuan, Meisong Liao, Tonglei Cheng, Xiaojie Xue, Takenobu Suzuki, Yasutake Ohishi
We investigate the supercontinuum (SC) generation in an 1 cm long silica photonic crystal fiber (PCF) pumped by the pulse sources with single, dual, and triple wavelengths, respectively. The silica PCF has two zero-dispersion wavelengths at 900 and 2620 nm, respectively. When pumped by a single wavelength, the SC spectral range covers about 1000 nm. When pumped by dual and triple wavelengths, the SC spectral range covers wider than 2000 nm. Both the SC spectral range and the flatness are improved obviously when pumped by triple wavelengths...
November 20, 2016: Applied Optics
Xuehan Zheng, Zhenzhong Wei, Guangjun Zhang
The theodolite is an important optical measurement instrument in application. Its global calibration, including position and orientation, is a prerequisite for measurement. Most global calibration methods require the theodolite to be leveled precisely, which is time-consuming and susceptible to error. We propose a global calibration method without leveling: it solves position results using the angular distance of control points by nonlinear optimization and then computes orientation parameters (rotation matrix) linearly based on position results...
November 20, 2016: Applied Optics
Robert Foster, Alexander Gilerson
A method is developed to determine the underwater polarized light field from above sea surface observations. A hybrid approach combining vector radiative transfer simulations and the Monte Carlo method is used to determine the transfer functions of polarized light for wind-driven ocean surfaces. Transfer functions for surface-reflected skylight and upward transmission of light through the sea surface are presented for many common viewing and solar geometries for clear-sky conditions. Sensitivity of reflection matrices to environmental conditions is examined and can vary up to 50% due to wind speed, 25% due to atmospheric aerosol load, and 10% due to radiometer field-of-view...
November 20, 2016: Applied Optics
Chenggang Zhu, Ru Chen, Yuzhangyang Zhu, Xu Wang, Xiangdong Zhu, Lan Mi, Fengyun Zheng, Yiyan Fei
Oblique-incidence reflectivity difference (OI-RD) is a form of polarization-modulation ellipsometry that measures properties of thin films on a solid surface through the change in polarization state of light upon reflection from the surface. The measurement accuracy depends on the precision of the phase modulation amplitude and azimuthal alignments of key polarizing optical elements and, thus, requires careful calibration. In the present work, we describe robust methods of such calibrations that enable precise determination of the modulation amplitude and static retardation of a phase modulator and azimuths of key polarizing optics in an OI-RD system...
November 20, 2016: Applied Optics
Christina Hesseling, Tim Homeyer, Joachim Peinke, Gerd Gülker
The intensity and phase reconstructed from digital in-line holograms by the convolution approach are analyzed. Distortions of particle images depending on their position in the plane transverse to the optical axis are identified. For this purpose, the object fields of numerically simulated particle holograms as well as of experimental data are reconstructed. The results of three-dimensional correlations of numerical and experimental data are superior when the numerically generated reference volumes are adapted to the transverse locations of the particle...
November 20, 2016: Applied Optics
Jonghwan Lee, Yasemin Gursoy-Ozdemir, Buyin Fu, David A Boas, Turgay Dalkara
Although progress has been made for recanalization therapies after ischemic stroke, post-treatment imaging studies show that tissue reperfusion cannot be attained despite satisfactory recanalization in a significant percentage of patients. Hence, investigation of microcirculatory changes in both surface and deep cortical levels after ischemia reperfusion is important for understanding the post-stroke blood flow dynamics. In this study, we applied optical coherence tomography (OCT) imaging of cerebral blood flow for the quantification of the microcirculatory changes...
November 20, 2016: Applied Optics
Sergio Alvarez-Rodríguez, Noé Alcalá Ochoa
In this work a novel polyphase optical encoder is presented, which uses a mathematical algorithm to take advantage of the polarization properties of light. This optical encoder has excellent accuracy, precision, and resolution in measuring the angular position of a shaft. Furthermore, it is designed to work with low-cost optical components. Initially, a light beam passes through a rotating polarizer, and readings are obtained from low-cost photoresistors located under phase shifted analyzers to generate characteristic curves for each of the phases, in the plane formed by the measured angle and the intensity of light...
November 20, 2016: Applied Optics
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