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Quantitative evaluation on internal seeing induced by heat-stop of solar telescope

OPTICS EXPRESS 2015年第15期23卷 19980-19995页

作者： Liu, Yangyi Gu, Naiting Rao, Changhui Chinese Acad Sci Inst Opt & Elect Lab Adapt Opt Chengdu 610209 Peoples R China Chinese Acad Sci Key Lab Adapt Opt Chengdu 610209 Peoples R China Chinese Acad Sci Grad Univ Beijing 100049 Peoples R China

heat-stop is one of the essential thermal control devices of solar telescope. The internal seeing induced by its temperature rise will degrade the imaging quality significantly. For quantitative evaluation on internal seeing, an integrated analysis method based on computational fluid dynamics and geometric optics is proposed in this paper. Firstly, the temperature field of the heat-affected zone induced by heat-stop temperature rise is obtained by the method of computational fluid dynamics calculation. Secondly, the temperature field is transformed to refractive index field by corresponding equations. Thirdly, the wavefront aberration induced by internal seeing is calculated by geometric optics based on optical integration in the refractive index field. This integrated method is applied in the heat-stop of the Chinese Large Solar Telescope to quantitatively evaluate its internal seeing. The analytical results show that the maximum acceptable temperature rise of heat-stop is up to 5 Kelvins above the ambient air at any telescope pointing directions under the condition that the root-mean-square of wavefront aberration induced by internal seeing is less than 25nm. Furthermore, it is found that the magnitude of wavefront aberration gradually increases with the increase of heat-stop temperature rise for a certain telescope pointing direction. Meanwhile, with the variation of telescope pointing varying from the horizontal to the vertical direction, the magnitude of wavefront aberration decreases at first and then increases for the same heat-stop temperature rise. (C) 2015 Optical Society of America

关键词： Astronomical telescopes computation methods Geometric optics Large telescopes Solar telescopes Wavefront aberrations

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Analytical brightness compensation algorithm for traditional polygon-based method in computer-generated holography

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APPLIED OPTICS 2013年第18期52卷 4391-4399页

作者： Pan, Yijie Wang, Yongtian Liu, Juan Li, Xin Jia, Jia Zhang, Zhao Beijing Inst Technol Sch Optoelect Beijing 100081 Peoples R China Virginia Tech Bradley Dept Elect & Comp Engn Blacksburg VA 24061 USA

In three-dimensional (3D) holographic display, current brightness compensation algorithm of the traditional polygon-based method experimentally obtains the compensation factor, which depends on the fabrication process. In this paper, we proposed an analytical brightness compensation method discarding the influence of the fabrication. The surface property function with the flat power spectral density and the compensation factor obtained from the simplified relationship between the original and the rotated frequencies are used to analytically compensate the radiant energy of the tilted polygon. The optical reconstruction results show the proposed method could effectively compensate the brightness and ensure the further shading process. The proposed method separates the brightness compensation from the fabrication process, which is important for deepening the investigation of the hologram fabrication and achieving realistic 3D reconstruction. (C) 2013 Optical Society of America

关键词： Brightness computation methods Diode pumped lasers Fast Fourier transforms Holographic displays Power spectral density

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Flow-mediated dilatation test using optoacoustic imaging: a proof-of-concept

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BIOMEDICAL OPTICS EXPRESS 2017年第7期8卷 3395-3403页

作者： Karlas, Angelos Reber, Josefine Diot, Gael Bozhko, Dmitry Anastasopoulou, Maria Ibrahim, Tareq Schwaiger, Markus Hyafil, Fabien Ntziachristos, Vasilis HelmholtzZentrum Munchen Inst Biol & Med Imaging D-85764 Neuherberg Germany TUM Munich Sch Bioengn D-81675 Munich Germany Klinikum Rechts Der Isar Dept Cardiol Ismaningerstr 22 D-81675 Munich Germany Klinikum Rechts Der Isar Dept Nucl Med Ismaningerstr 22 D-81675 Munich Germany Univ Diderot Bichat Univ Hosp Dept Nucl Med Inserm 1148 Paris France

Label-free multispectral optoacoustic tomography (MSOT) has recently shown superior performance in visualizing the morphology of human vasculature, especially of smaller vessels, compared to ultrasonography. Herein, we extend these observations towards MSOT interrogation of macrovascular endothelial function. We employed a real-time handheld MSOT scanner to assess flow-mediated dilatation (FMD), a technique used to characterize endothelial function. A data processing scheme was developed to quantify the dimensions and diameter changes of arteries in humans and determine wall distensibility parameters. By enabling high-resolution delineation of the blood-vessel wall in a crosssectional fashion, the findings suggest MSOT as a capable alternative to ultrasonography for clinical FMD measurements. (C) 2017 Optical Society of America

关键词： Cardiovascular applications computation methods Detector arrays Image quality Temporal resolution Tomographic image reconstruction

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QUANTUM-CLASSICAL CORRESPONDENCES FOR ATOMIC OPERATORS - A POSITIVE-P REPRESENTATION APPROACH

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JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS 1995年第10期12卷 1774-1782页

作者： YOU, L COOPER, J ZOLLER, P UNIV COLORADO NATL INST STAND & TECHNOLJOINT INST LAB ASTROPHYSBOULDERCO 80309

We demonstrate the successful simulation of classical stochastic differential equations obtained from the positive P phase-space technique for two-level atoms pumped by a near-resonant laser. Numerical results for both the resonance fluorescence spectrum and the absorption spectrum are compared with the exact results. (C) 1995 Optical Society of America

关键词： Absorption spectroscopy Coherent states computation methods Numerical simulation Resonance fluorescence Spontaneous emission

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Fast iterative tomographic wavefront estimation with recursive Toeplitz reconstructor structure for large-scale systems

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JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS IMAGE SCIENCE AND VISION 2018年第8期35卷 1330-1345页

作者： Ono, Yoshito H. Correia, Carlos Conan, Rodolphe Blanco, Leonardo Neichel, Benoit Fusco, Thierry Natl Astron Observ Japan Subaru Telescope 650 North Aohoku Pl Hilo HI 96720 USA Aix Marseille Univ CNRS CNES LAM Marseille France GMTO Corp 465 N Halstead StSuite 250 Pasadena CA 91107 USA Off Natl Etud & Rech Aerosp F-92322 Chatillon France

Tomographic wavefront reconstruction is the main computational bottleneck to realize real-time correction for turbulence-induced wavefront aberrations in future laser-assisted tomographic adaptive-optics (AO) systems for ground-based giant segmented mirror telescopes because of its unprecedented number of degrees of freedom, N, i.e., the number of measurements from wavefront sensors. In this paper, we provide an efficient implementation of the minimum-mean-square error (MMSE) tomographic wavefront reconstruction, which is mainly useful for some classes of AO systems not requiring multi-conjugation, such as laser-tomographic AO, multi-object AO, and ground-layer AO systems, but is also applicable to multi-conjugate AO systems. This work expands that by Conan [Proc. SPIE 9148, 91480R (2014)] to the multi-wavefront tomographic case using natural and laser guide stars. The new implementation exploits the Toeplitz structure of covariance matrices used in an MMSE reconstructor, which leads to an overall O(N log N) real-time complexity compared with O(N-2) of the original implementation using straight vector-matrix multiplication. We show that the Toeplitz-based algorithm leads to 60 nm rms wavefront error improvement for the European Extremely Large Telescope laser-tomography AO system over a well-known sparse-based tomographic reconstruction;however, the number of iterations required for suitable performance is still beyond what a real-time system can accommodate to keep up with the time-varying turbulence. (C) 2018 Optical Society of America.

关键词： Atmospheric turbulence computation methods Laser guide stars Numerical simulation Phase space analysis methods Wavefront aberrations

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Multi-level height maps-based registration method for sparse LiDAR point clouds in an urban scene

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APPLIED OPTICS 2021年第14期60卷 4154-4164页

作者： Fang, Bin Ma, Jie An, Pei Wang, Zhao Zhang, Jun Yu, Kun Huazhong Univ Sci & Technol HUST Sch Artificial Intelligence & Automat Wuhan 430074 Hubei Peoples R China HUST Natl Key Lab Sci & Technol Multispectral Informat Wuhan 430074 Hubei Peoples R China

The LiDAR sensor has been widely used for reconstruction in urban scenes. However, the current registration method makes it difficult to find stable 3D point correspondences from sparse and low overlapping LiDAR point clouds. In the urban situation, most of the LiDAR point clouds have a common flat ground. Therefore, we propose a novel, to the best of our knowledge, multi-level height (MH) maps-based coarse registration method. It requires that source and target point clouds have a common flat ground, which is easily satisfied for LiDAR point clouds in urban scenes. With MH maps, 3D registration is simplified as 2D registration, increasing the speed of registration. Robust correspondences are extracted in MH maps with different height intervals and statistic height information, improving the registration accuracy. The solid-state LiDAR Livox Mid-100 and mechanical LiDAR Velodyne HDL-64E are used in real-data and dataset experiments, respectively. Verification results demonstrate that our method is stable and outperforms state-of-the-art coarse registration methods for the sparse case. Runtime analysis shows that our method is faster than these methods, for it is non-iterative. Furthermore, our method can be extended for the unordered multi-view point clouds. (C) 2021 Optical Society of America

关键词： Clouds computation methods Laser scanning Lidar Object detection Sensors

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Design of a curved-target ultrashort throw projector based on predistortion and illumination precorrection

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APPLIED OPTICS 2023年第29期62卷 7837-7843页

作者： Cheng, Dewen Liu, Yue Chen, Hailong Chen, Chen Wang, Yongtian Beijing Inst Technol Beijing Engn Res Ctr Mixed Real & Adv Display Sch Opt & Photon Beijing 100081 Peoples R China Xi An Jiao Tong Univ Key Lab Phys Elect & Devices Minist Educ Xian 710049 Peoples R China Xi An Jiao Tong Univ Shaanxi Key Lab Informat Photon Tech Xian 710049 Peoples R China Shang Hai OE Technol Co LTD Shanghai 200333 Peoples R China

Ultrashort throw projector (UTP) technology has been a challenging research focus in the fields of large field of view and short -distance projection. In this paper, we propose a design method for a curved -target UTP based on image precorrection. A predistortion method (<1 pixel) using a radial basis function is presented to effectively correct irregular distortion. A grayscale precorrection method is used to address uneven illumination distribution. We provide a UTP design example and verify the correction methods using two different curved targets (aspherical and freeform), demonstrating effective distortion correction (<1%) and illumination uniformity (>90%). The structure similarity index measure for the projection images shows close or greater than 0.9 correlation. (c) 2023 Optica Publishing Group

关键词： computation methods Distortion Freeform lenses Image metrics Optical design Ray tracing

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Radiation of a uniformly moving line charge in a zero-index metamaterial and other periodic media

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OPTICS EXPRESS 2012年第16期20卷 18515-18524页

作者： Yanai, Avner Levy, Uriel Hebrew Univ Jerusalem Dept Appl Phys Benin Sch Engn & Comp Sci IL-91904 Jerusalem Israel

Radiation of electromagnetic waves by a uniformly moving charge is the subject of extensive research over the last several decades. Fascinating effects such as Vavilov-Cherenkov radiation, transition radiation and the Smith-Purcell effect were discovered and studied in depth. In this paper we study the radiation of a line charge moving with relativistic constant velocity within an average zero index metamaterial consisting of periodically alternating layers with negative and positive refractive index. We observe a strong radiation enhancement, (similar to)3 orders of magnitude, for specific combinations of velocities and radiation frequencies. This surprising finding is attributed to a gigantic increase in the density of states at the positive/negative index boundary. Furthermore, we shed light on radiation effects of such a line charge propagating within the more "traditional" structure of periodically alternating layers consisting of positive and different refractive index with focus on frequencies satisfying the quarter wave stack and the half wave stack conditions. We show that the quarter-wave-stack case results in emission propagating vertically to the line charge trajectory, while the half-wave-stack results in negligible radiation. All these findings were obtained using a computationally efficient and conceptually intuitive computation method, based on eigenmode expansion of specific frequency components. For validation purposes this method was compared with the finite-difference-time-domain method. (C) 2012 Optical Society of America

关键词： computation methods Electromagnetic radiation Phase velocity Refractive index Rigorous coupled wave analysis Spatial frequency

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Accurate method for computing correlated color temperature

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OPTICS EXPRESS 2016年第13期24卷 14066-14078页

作者： Li, Changjun Cui, Guihua Melgosa, Manuel Ruan, Xiukai Zhang, Yaoju Ma, Long Xiao, Kaida Luo, M. Ronnier Wenzhou Univ Wenzhou 325035 Peoples R China Univ Sci & Technol Liaoning Anshan 114051 Peoples R China Univ Granada Dept Opt E-18071 Granada Spain Shenyang Jianzhu Univ Shenyang 110168 Peoples R China Univ Leeds Leeds LS2 9JT W Yorkshire England

For the correlated color temperature (CCT) of a light source to be estimated, a nonlinear optimization problem must be solved. In all previous methods available to compute CCT, the objective function has only been approximated, and their predictions have achieved limited accuracy. For example, different unacceptable CCT values have been predicted for light sources located on the same isotemperature line. In this paper, we propose to compute CCT using the Newton method, which requires the first and second derivatives of the objective function. Following the current recommendation by the International Commission on Illumination (CIE) for the computation of tristimulus values (summations at 1 nm steps from 360 nm to 830 nm), the objective function and its first and second derivatives are explicitly given and used in our computations. Comprehensive tests demonstrate that the proposed method, together with an initial estimation of CCT using Robertson's method [J. Opt. Soc. Am. 58, 1528-1535 (1968)], gives highly accurate predictions below 0.0012 K for light sources with CCTs ranging from 500 K to 10(6) K. (C) 2016 Optical Society of America

关键词： CIE color spaces Color computation methods Light sources Range finding Temperature

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Finite element simulation of light transfer in turbid media under structured illumination

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APPLIED OPTICS 2017年第21期56卷 6035-6042页

作者： Hu, Dong Lu, Renfu Ying, Yibin Zhejiang Univ Coll Biosyst Engn & Food Sci 866 Yuhangtang Rd Hangzhou 310058 Zhejiang Peoples R China ARS USDA 524 S Shaw Lane E Lansing MI 48824 USA Michigan State Univ Biosyst & Agr Engn 524 S Shaw Lane E Lansing MI 48824 USA Zhejiang A&F Univ Coll Engn 88 Huanchengbei RdHangzhou Rdngzhou 311300 Zhejiang Peoples R China

The spatial-frequency domain (SFD) imaging technique allows us to estimate the optical properties of biological tissues in a wide field of view. The technique is, however, prone to error in measurement because the two crucial assumptions used for deriving the analytical solution to the diffusion approximation cannot be met perfectly in practical applications. This research mainly focused on modeling light transfer in turbid media under the normal incidence of structured illumination using the finite element method ( FEM). Finite element simulations were performed for 50 simulation samples with different combinations of optical absorption and scattering coefficients for varying spatial frequencies, and the results were then compared with the analytical method and Monte Carlo simulation. Relationships between diffuse reflectance and dimensionless absorption and dimensionless scattering coefficients were investigated. The results indicated that the FEM provided reasonable results for diffuse reflectance, compared with the analytical method. Both the FEM and the analytical method overestimated the reflectance for mu(tr)/f(x) values of greater than 2 and underestimated the reflectance for mu(tr)/f(x) values of smaller than 2. Larger values of mu(s)'/mu(a) yielded better diffuse reflectance estimations than did those of smaller than 10. The reflectance increased nonlinearly with the dimensionless scattering, whereas the reflectance decreased linearly with the dimensionless absorption. It was also observed that diffuse reflectance was relatively stable and insensitive to mu(s)' when the dimensionless scattering was larger than 50. Overall results demonstrate that the FEM is effective for modeling light transfer in turbid media and can be used to explore the effects of crucial parameters for the SFD imaging technique. (C) 2017 Optical Society of America

关键词： computation methods Diffuse reflectance Multiple scattering Spatial frequency Tissue optical properties Turbid media

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