Phase retrieval for high-numerical-aperture optical systems

We describe a phase retrieval approach for intensity point-spread functions of high-numerical-aperture optical systems such as light microscopes. The method calculates a generalized pupil function defined on a spherical shell, using measured images at several defocus levels. The resultant pupil functionsreproduce measured point-source images significantly better than does an ideal imaging model. Availability of pupil function information will facilitate new approaches to aberration correction in such systems.     

Phase retrieval algorithm for optical information security

As a typical technology for optical encryption, phase retrieval algorithms have been widely used in optical information encryption and authentication systems. This paper presents three applications of two-dimensional(2D) phase retrieval for optical encryption and authentication: first, a hierarchical image encryption system, by which multiple images can be hidden into cascaded multiple phase masks; second, a multilevel image authentication system, which combines(t, n) threshold secret sharing(both t and n are positive integers, and t ≤ n) and phase retrieval, and provides both high-level and low-level authentication; and finally, a hierarchical multilevel authentication system that combines the secret sharing scheme based on basic vector operations and the phase retrieval, by which more certification images can be encoded into multiple cascaded phase masks of different hierarchical levels. These three phase retrieval algorithms can effectively illustrate phase-retrievalbased optical information security. The principles and features of each phase-retrieval-based optical security method are analyzed and discussed. It is hoped that this review will illustrate the current development of phase retrieval algorithms for optical information security and will also shed light on the future development of phase retrieval algorithms for optical information security.     

Phase retrieval in optical fiber modal interference for structural health monitoring

A method based on data dependent system (DDS) for extraction of phase in fiber modal interference is presented. The interference patterns of LP₀₁ & LP₁₁, LP₀₁ & LP₀₂ and LP₀₆ &LP₀₇ within the fiber have been recorded under different launching conditions. The patterns were characterized by means of autoregressive model and the self coherence functions of the corresponding interferogram were determined. It would provide the phase distribution of the pattern and the modulation of group delay due to the measurand. An application has been made for measuring strain in a simply supported beam under different loading conditions. Results are presented for the applied strain in the range of 270-1500 μ strain.     

Phase retrieval

The problem of phase retrieval arises in experimental uses of diffraction to determine intrinsic structure because the modulus of a Fourier transform is all that can usually be measured after diffraction occurs. For finite distributions, the phase retrieval problem can be solved by methods of factorization in suitable rings of polynomials; for continuous distributions with compact support, the methods of complex analysis are needed to solve the phase retrieval problem. These methods are discussed and examples are given for illustration.Partially supported by NSF Grant MCS 8218800     

Multiple-encoding retrieval for optical security

We propose a method for image encryption by multiple-step random phase encoding with an undercover multiplexing operation. The true image is stored in a multiple record we call encodegram; and then we can reconstruct it by the use of the appropriate random phase masks and a retrieval protocol. To increase the security of the true hidden image and confuse unauthorized receivers, we add to the encodegram an encoded fake image with different content. This fake image has only a small effect on the retrieval of the true hidden image, owing to the specific property of this protocol. In the decryption step, we can reveal the true image by applying the inverse protocol to two cyphertexts, one the encodegram containing the true image along with the fake image; and the other helping to get the random phase key to achieve the true image. Computer simulations verify the validity of this method for image encryption. Digital implementation of the method makes it particularly suitable for the remote transmission of information.     

Phase retrieval of optical fringe patterns from the ridge of a wavelet transform

A new method for phase retrieval of optical fringe patterns is presented. This method is based on a wavelet transform and is capable of extracting the full 2D phase distribution from a single fringe pattern. An important conclusion that the phase of the optical fringe pattern is equal to the phase of its wavelet transform on the ridge of the wavelet transform is theoretically clarified. The method is compared with the Fourier transform and the integration methods. A numerical simulation and an experimental example of phase retrieval are shown.     

An optical method for measuring nanoparticle size

We describe a method for determining the size of nanoparticles and their optical constants that is based on analysis of the spectrum of extinction of light by these particles. We show that the results of our mathematical modeling agree well with the experimental data.     

光学元件高反射比、高透射比测试技术研究

 为了实现光学元件、光学薄膜等高反射比、高透射比的测量,以单次反射测量法为基础,并结合激光稳功率技术、双光路测量技术以及精密探测技术,建立了一套精密测试系统,实现对光学元件632.8 nm和1 064 nm两个波长下高反射比与高透射比的测量。实验和测量不确定度分析验证测试系统在632.8 nm波长下高反射比与高透射比的测量不确定度优于0.008%,在1 064 nm波长下高反射比与高透射比的测量不确定度优于0.015%。     

Phase retrieval in DSSI for relatively large deformation

Methods for phase retrieval in digital speckle shearing interferometry (DSSI) with relatively large deformation are proposed using a single wavelength illumination with windowed Fourier filtering (WFF) and two-wavelength simultaneous illumination with iterative sine-cosine average filtering (ISCAF). For relatively large deformation measurement, WFF technique has a higher noise suppression capability than ISCAF technique but requires careful selection of the processing parameters, while ISCAF is a simple filtering with less parameter setting. Both methods for phase retrieval are discussed. Experimental results show that both methods are capable of noise suppression in the phase retrieval for relatively large deformation.     

Phase retrieval by pinhole scanning

We describe a method where phase and amplitude of a wavefront are obtained by processing a sequence of pattern produced by the interference between the light transmitted by a scanning pinhole (which is sequentially shifted) and a reference pinhole. Simulations and experimental results are presented.     

Polarization imaging in atmospheric environment based on polarized reflectance retrieval

A method for calculating the atmospheric parameters measurement accuracy requirement based on polarized reflectance retrieval is proposed. The at-sensor polarization states with different atmospheric parameters content are simulated based on the atmospheric radiative transfer model in order to select the key parameter affecting the polarization observation. The accuracy requirement of atmospheric parameters is derived through the polarized reflectance retrieval method. Experiment results show that retrieval accuracy of polarized reflectance of typical ground objects can be up to 90%. The atmospheric parameters measurement accuracy requirement when the retrieval accuracy is more than 75% is derived.     

硬x射线同轴相衬成像的相位恢复

基于角谱的概念，分析了硬x射线同轴相衬成像过程，在传统相位恢复算法GS算法的基础上 ，提出了基于角谱传播的相位恢复算法——迭代角谱法（IASA），并利用数值法模拟研究了 相衬成像和相位恢复过程，从理论上验证了这一相位恢复算法. 关键词： 相位恢复 相位衬度 角谱 硬x射线     

Research of reflectance photometer based on optical absorption

Gold-labeled lateral flow (LF) assay has been studied extensively due to its sensitiveness, simpleness, and rapidness. In this paper, scattering properties of nanogold particles and LF strip were analyzed. Based on the above analysis, a reflectance photometer has been developed for LF strip labeled by nanogold particles. The integration of reflection optical density was used to indicate the signal of T line and C line. A quantitative equation for cardiac troponin I (cTnI) was deduced to realize quantification of the real cTnI sample, whose correlation of coefficient (R²) was 0.989. The variation coefficient (CV) of repetitive experiments was less than 5%. The reflectance photometer was simple, sensitive, stable, and suitable for field detection.     

Phase retrieval using multiple illumination wavelengths

An iterative phase retrieval method is proposed, which uses a sequence of diffraction intensity patterns recorded at different wavelengths. This method has a rapid convergence, and a high immunity to noise and environmental disturbance. The wrap-free phase measurement range is also extended based on the principle of two-wavelength interferometry. Simulation and experimental results are presented to demonstrate the approach.     

Phase retrieval low energy electron microscopy

We consider the utility of phase-retrieval methods in low energy electron microscopy (LEEM). Computer simulations are presented, demonstrating recovery of the terraced height profile of atomic steps. This recovery uses phase retrieval to decode a single LEEM image, incorporating the effects of defocus, spherical aberration and chromatic aberration. The ability of the method, to obtain temporal sequences of evolving step profiles from a single LEEM movie, is discussed.     

Phase retrieval in low-coherence interferometric microscopy

We present compensating methods that address inherent errors in quantitative phase reporting for low-coherence interferometric techniques. A brief theoretical treatment of the problem and experimental validation using spectral domain phase microscopy demonstrate mitigation of the degrading effects of phase leakage on accurate measurement of optical path length in the vicinity of closely spaced reflectors. This result has direct implications for phase-sensitive interferometry techniques, such as Doppler imaging, as well as amplitude-based quantitative reporting. Corrected phase retrieval is demonstrated for conversion of interferometric phase to optical path length in cell surface deflections of beating cardiomyocytes.     

高光谱传感器光谱性能参数反演与反射率恢复

在轨高光谱传感器光谱性能参数的准确定标是数据定量应用的基本前提。文章在前人基础上,综合优化算法,实现了在不需要实测地表反射率的情况下,同时反演高光谱传感器中心波长与半值波宽(fullwidth at half maximum,FWHM)。基于模拟数据的研究结果显示,该方法在光谱性能参数偏移5 nm时,中心波长反演误差小于0.1 nm,FWHM误差小于0.7 nm。将该方法应用于Hyperion数据,结果显示,Hype-rion在VNIR谱段存在明显的smile效应,在整个CCD阵列范围内,其中心波长的偏移量在-2~2 nm之间,FWHM偏移在-0.2~0.5 nm之间;在SWIR谱段smile效应不明显,其中心波长偏移3 nm左右,FWHM偏移在-2~-3 nm之间。最后在光谱重定标基础上,对Hyperion进行了大气校正,反演了不受大气及定标参数影响的地表反射率。经光谱重定标,在大气吸收波段周围由光谱定标参数变化导致的反射率突变得到了抑制。