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Applied Optics

Yue Zhao, Yuanzhen Li, Bihui Zheng
Two methods are presented for calibrating a paracatadioptric camera. A sphere in 3D space is projected to two parallel circles on which two tangents of a point and its antipode are parallel on the unit viewing sphere and intersect at the point at infinity. The direction of the polar of the point at infinity is orthogonal to the direction of the point at infinity with respect to the circle. The imaged circular points and orthogonal vanishing points can be obtained to solve the intrinsic camera parameters. Simulations and real data were used to demonstrate the effectiveness of the two algorithms...
May 20, 2018: Applied Optics
F Chavez-Gutierrez, A Martinez-Rios, D Toral-Acosta, D Torres-Armenta, J A Guerrero-Viramontes
The simultaneous measurement of the numerical aperture (NA) and mode field diameter (MFD) of single-mode fibers was performed on several commercial fibers by means of digital image processing of the output light projected into a screen. In addition, the changes induced by core diffusion in an ultra-high (UH) NA fiber at several heat depositions from a CO2 laser source were measured. The measurement method was demonstrated to be useful to monitor the adiabaticity of this process, by taking the product of the NA and MFD to verify if it remains constant...
May 20, 2018: Applied Optics
Biswajit Medhi, Gopalakrishna M Hegde, Kalidevapura Jagannath Reddy, Debasish Roy, Ram Mohan Vasu
A method for quantitative estimation of density variation in high-speed flow, which uses light as an interrogating tool, is described. The wavefront distortion of the interrogating beam induced by the compressible flow field is estimated quantitatively, in which the density gradient of the flow field is seen as refractive-index gradient by the probing beam. The distorted wavefront is measured quantitatively by using the cross-sectional intensities of the distorted wavefront along the optical axis. Iterative algorithms are developed using both deterministic (Gauss-Newton) and stochastic (ensemble Kalman filter) update strategies to recover unknown parameters such as the phase of the wavefront or the refractive index distribution in the flow directly from the measured intensities...
May 20, 2018: Applied Optics
Vladimir Liberman, Melissa Smith, Isaac Weaver, Mordechai Rothschild
Nanofluidic channels are of great interest for DNA sequencing, chromatography, and drug delivery. However, metrology of embedded or sealed nanochannels and measurement of their fill-state have remained extremely challenging. Existing techniques have been restricted to optical microscopy, which suffers from insufficient resolution, or scanning electron microscopy, which cannot measure sealed or embedded channels without cleaving the sample. Here, we demonstrate a novel method for accurately extracting nanochannel cross-sectional dimensions and monitoring fluid filling, utilizing spectroscopic ellipsometric scatterometry, combined with rigorous electromagnetic simulations...
May 20, 2018: Applied Optics
Roopa Venkataraj, Arindam Sarkar, C P Girijavallabhan, P Radhakrishnan, V P N Nampoori, M Kailasnath
The present work describes an energy-transfer-based fluoride sensor using the highly photo-stable Coumarin 540a (C540a)-Rhodamine 6g (Rh6g) dye pair. Rh6g exhibits a decrease in fluorescence emission, whereas C540a shows no change in response to fluoride. The increase in fluoride concentration decreases the energy transfer efficiency between the C540a donor and Rh6g acceptor in acetonitrile, leading to a subsequent recovery of fluorescence emission from C540a molecules. The sensing mechanism using fluorescence resonance energy transfer is found to be highly specific towards fluoride detection when compared to the response towards other anions...
May 20, 2018: Applied Optics
J A Arriaga-Hernández, F Granados-Agustín, A Cornejo-Rodríguez
In this paper, we use the irradiance transport equation and the Fourier transform-based experimental solution given by Ichikawa-Lohmann-Takeda. We analyze experimental factors such as the digital filter, the introduced error for the rotation and period of the Ronchi ruling, and a new method is demonstrated for the measurement of 3D wavefront information.
May 20, 2018: Applied Optics
Jian Liu, Xiaoyu You, Yuhang Wang, Chenguang Liu, Jiubin Tan
α-β circular scanning with a large scanning field of view and high reliability can be widely applied in laser scanning imaging systems and laser processing. However, mechanical inertia of the galvanometers introduces phase delay and ultimately leads to scanning distortions in α-β circular scanning in both constant angular velocity scanning (CAVS) and constant line velocity scanning (CLVS). To compensate for the phase-delay distortions, two correction models are respectively proposed for CAVS and CLVS, which utilize phase-frequency relationships based on the galvanometer's transfer function...
May 20, 2018: Applied Optics
Nathan Hagen, Yukitoshi Otani
We calculate the photometric Stokes parameter covariance matrices and SNRs estimated by polarimeters exposed to general noise distributions, such as mixed Poisson-Gaussian (PG) noise. The measurement model includes the effects of optical losses and detector quantum efficiency, enabling quantitative comparison of instruments that have different photometric efficiencies. We demonstrate this capability by comparing the performance of many common polarimeter configurations, including diattenuator-based systems, such as Azzam's four-detector polarimeter [Opt...
May 20, 2018: Applied Optics
Yue Hu, Ying Xiong, Xiangyu Chen, Haobo Bai, Yangchao Tian, Gang Liu
A novel method to fabricate a microlens array with a long focal length has been developed in this paper. It is based on the fabricating and heating of a microlens consisting of two materials with a great difference in coefficient of thermal expansion. A thermal expansion process leads to considerable deformation of the microlens surface and significant increase in focal length, which could be controlled by altering the processing temperature. Cylindrical polymeric microlens arrays with different focal lengths were successfully fabricated...
May 20, 2018: Applied Optics
Li Rao, Feipeng Da
We introduce a flexible error correction method for fringe projection profilometry (FPP) systems in the presence of local blur phenomenon. Local blur caused by global light transport such as camera defocus, projector defocus, and subsurface scattering will cause significant systematic errors in FPP systems. Previous methods, which adopt high-frequency patterns to separate the direct and global components, fail when the global light phenomenon occurs locally. In this paper, the influence of local blur on phase quality is thoroughly analyzed, and a concise error correction method is proposed to compensate the phase errors...
May 20, 2018: Applied Optics
Antonín Mikš, Jiří Novák
The formulas are derived for calculation of the third-order aberration (Seidel) coefficients for a thick spherical lens in air with a given value of its focal length and for an object at infinity in this paper. The explicit analytic dependence of individual aberration coefficients on a lens thickness is derived. Equations were described for the re-calculation of aberration coefficients for a different value of focal length and different values of entrance pupil and object positions. Such formulas make it possible to analyze analytically an influence of the lens thickness on lens aberration properties and the replacement of a thin lens optical system by a thick lens model...
May 20, 2018: Applied Optics
Yu Zhao, Ki-Chul Kwon, Munkh-Uchral Erdenebat, Md-Sifatul Islam, Seok-Hee Jeon, Nam Kim
The calculation of realistic full-color holographic displays is hindered by the high computational cost. Previously, we suggested a point cloud gridding (PCG) method to calculate monochrome holograms of real objects. In this research, a relocated point cloud gridding (R-PCG) method is proposed to enhance the reconstruction quality and accelerate the calculation speed in GPU for a full-color holographic system. We use a depth camera to acquire depth and color information from the real scene then reconstruct the point cloud model virtually...
May 20, 2018: Applied Optics
Yanfei Hao, Mingying Sun, Zhaoyang Jiao, Yajing Guo, Xue Pan, Xiangyang Pang, Jianqiang Zhu
We propose two efficient methods of determining damage growth threshold (DGT) based on the saturation damage size analysis (SDSA) for multilayer dielectric gratings by picosecond pulsed lasers. The damage size at laser fluences above DGT increases with the shot number and finally saturates due to the Gaussian focal spot. The DGT is extracted by mapping the boundary of a saturation damage site obtained at single fluence to the beam profile, which is called the monofluence SDSA method. Meanwhile, the saturation damage size decreases when reducing laser fluence...
May 20, 2018: Applied Optics
Lin Zhang, Wenchen Zhou, Neil J Naples, Allen Y Yi
Chalcogenide glasses are emerging as alternative materials for low-cost and high-volume glass molding processes for infrared optics. In precision glass molding, it is well documented that the refractive index variation in the molded elements can lead to substantial amounts of aberrations. The variation has such a significant effect that the optical designs with molded lenses need to be carefully considered and compensated for index variation to achieve targeted optical performance. This research is aimed to evaluate the refractive index change of a chalcogenide glass during the molding process by both finite element method-based simulation and optical experiment...
May 20, 2018: Applied Optics
Pan Zhang, Hangzhou Yang, Kok-Sing Lim, Harith Ahmad, Qiangzhou Rong, Qin Tian, Xiangzi Ding
An in-fiber Mach-Zehnder interferometer (MZI) is proposed and experimentally demonstrated for relative humidity (RH) and temperature measurements. The MZI is formed by a grapefruit-shaped photonic crystal fiber (G-PCF) cascaded with a short section of multimode fiber that serves as a mode coupler. To enhance sensitivity to humidity, femtosecond laser micromachining was performed to remove a portion of cladding of the G-PCF to expose its core to the ambient medium. The output interference spectrum is fast Fourier transformed to produce a spatial frequency spectrum that describes the intensity composition of the cladding modes in the MZI...
May 20, 2018: Applied Optics
Wenjun Zheng, Negar H Golshan, Sue-Jonnathane Celestin, Katherine S Ziemer, Ming Su
Metal ions in ground are hard to remove and constitute a serious environmental challenge. This paper reports a new laser-based method for in situ soil decontamination at high efficiency, in which a focused CO2 laser is used to oxidize metal contaminants from soil and fuse them with silica (base materials of soil), thus preventing undesired transport of metal ions within soil. Three types of metal ions (copper, nickel, and cadmium) adsorbed on porous silica plates are exposed to continuous laser irradiation...
May 20, 2018: Applied Optics
William O F Carvalho, Danilo H Spadoti, Enrique Silvestre, Felipe Beltran-Mejia
A photonic crystal fiber Mach-Zehnder interferometer design was optimized to obtain high performance and ultralow chirp. Two long-period gratings were used to excite the cladding modes, and the rich structure of the cladding was tailored to obtain a slightly chirped free spectral range, as required by the Telecommunication Standardization Sector of the International Telecommunication Union (ITU-T) Norm G.694.1. Finally, a fabrication tolerance analysis was performed. The advantages of the proposed device are an ultralow chirp, high bandwidth, and fabrication robustness tolerance...
May 20, 2018: Applied Optics
Yixuan Zhang, Chunqing Gao, Qing Wang, QuanXin Na, Mingwei Gao, Meng Zhang, Shuai Huang
A stable, 2.09 μm single-frequency Ho:YAG master oscillator and power amplifier (MOPA) system at a pulse repetition frequency of 1.25 kHz is demonstrated. The maximum output energy of the single-frequency injection-seeded laser is 13.76 mJ, and the corresponding pulse width is 178.9 ns. The seed laser is a continuous-wave Ho:YAG non-planar ring oscillator laser. The half-width of the pulse spectrum is measured to be 2.65 MHz by using the heterodyne technique, which is about 1.06 times Fourier transform limited...
May 20, 2018: Applied Optics
Zhili Zhao, Honghai Zhang, Sheng Liu, Xinzhong Wang
Most LED luminaires face the problem of color nonuniformity in illumination fields, which seriously degrades their lighting quality. To address this issue, we proposed a freeform TIR lens, which could be applied to the most widely adopted phosphor-converted LEDs and multicolor LED arrays. Based on light pattern overlap and energy mapping, the novel TIR lens comprised the freeform panel and the collimator. Analysis of angular color uniformity (ACU), based on a phosphor-converted white LED model, proved that the normalized standard deviation (NSD) of the LED integrated with the freeform TIR lens significantly decreased from 0...
May 20, 2018: Applied Optics
Jia Liu, Pinggang Jia, Huixin Zhang, Xiaodan Tian, Hao Liang, Yingping Hong, Ting Liang, Wenyi Liu, Jijun Xiong
In this study, a novel batch-producible fiber-optic Fabry-Perot (FP) pressure sensor based on a low-temperature co-fired ceramic technology is proposed and experimentally demonstrated for high-temperature applications. The sensor is fabricated by inserting a well-cut single-mode fiber (SMF) into a zirconia fiber ferrule, followed by insertion of the overall structure into an alumina sensor head. The FP cavity in the sensor is formed by placing the end face of the SMF in parallel to the diaphragm. The external pressure can be detected by demodulating the FP cavity length of the sensor...
May 20, 2018: Applied Optics
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