Cai Dongmei

Taiyuan University of Technology · Department of physics

The point spread function (PSF) reflects states of a telescope and plays an important role in development of data processing methods, such as PSF based astrometry, photometry and image restoration. However, for wide field small aperture telescopes (WFSATs), estimating PSF in any position of the whole field of view is hard, because aberrations induc...

The Shack–Hartmann wavefront sensor is widely used to measure aberrations induced by atmospheric turbulence in adaptive optics systems. However, if strong atmospheric turbulence exists or the brightness of guide stars is low, the accuracy of wavefront measurements will be affected. In this work, we propose a compressive Shack–Hartmann wavefront sen...

Image restoration methods are commonly used to improve the quality of astronomical images. In recent years, developments of deep neural networks and increments of the number of astronomical images have evoked a lot of data-driven image restoration methods. However, most of these methods belong to supervised learning algorithms, which require paired...

Image restoration methods are commonly used to improve the quality of astronomical images. In recent years, developments of deep neural networks and increments of the number of astronomical images have evoked a lot of data--driven image restoration methods. However, most of these methods belong to supervised learning algorithms, which require paire...

Ground based optical telescopes are seriously affected by atmospheric turbulence induced aberrations. Understanding properties of these aberrations is important both for instruments design and image restoration methods development. Because the point spread function can reflect performance of the whole optic system, it is appropriate to use the poin...

The point spread function reflects the state of an optical telescope and it is important for data post-processing methods design. For wide field small aperture telescopes, the point spread function is hard to model, because it is affected by many different effects and has strong temporal and spatial variations. In this paper, we propose to use the...

Ground based optical telescopes are seriously affected by atmospheric turbulence induced aberrations. Understanding properties of these aberrations is important both for instruments design and image restoration methods development. Because the point spread function can reflect performance of the whole optic system, it is appropriate to use the poin...

The point spread function reflects the state of an optical telescope and it is important for data post-processing methods design. For wide field small aperture telescopes, the point spread function is hard to model, because it is affected by many different effects and has strong temporal and spatial variations. In this paper, we propose to use the...

Space target images obtained by ground-based optical telescopes are blurred by atmospheric turbulence induced aberrations. Obtaining effective information from these highly blurred images has became an active research area. Because all space targets are human-made objects, they have only limited structure and shape. With some high resolution images...

Ground based optical telescopes are seriously affected by atmospheric turbulence induced aberrations. Understanding properties of these aberrations is important both for instruments design and image restoration methods development. Because the point spread function can reflect performance of the whole optic system, it is appropriate to use the poin...

The next generation of ground-based solar observations requires good image quality metrics for post facto processing techniques. Based on the assumption that texture features in solar images are multi-fractals and that they can be extracted by trained deep neural networks as feature maps, a new reduced-reference objective image quality metric, the...

Texture is one of the most obvious characteristics in solar images and it is normally described by texture features. Because textures from solar images of the same wavelength are similar, we assume texture features of solar images are multi-fractals. Based on this assumption, we propose a pure data-based image restoration method: with several high...

Compressive sensing is widely used in many different areas. The framework of compressive sensing can be divided into two parts: compressive sampling of signals and recovering original signals from the randomly sampled measurements. In this paper, we model the whole framework of compressive sensing with a deep neural network in a straightforward way...

Texture is one of the most obvious characteristics in solar images and it is normally described by texture features. In this paper, we assume texture features of solar images are multi-fractals and in the same wavelength, they satisfy the same probability distribution, regardless of their structural contents. With this assumption, we use several hi...

Next-generation ground-based solar observations require good image quality metrics for post-facto processing techniques. Based on the assumption that texture features in solar images are multi-fractal which can be extracted by a trained deep neural network as feature maps, a new reduced-reference objective image quality metric, the perception evalu...

Wide field small aperture telescopes are working horses for fast sky surveying. Transient discovery is one of their main tasks. Classification of candidate transient images between real sources and artifacts with high accuracy is an important step for transient discovery. In this paper, we propose two transient classification methods based on neura...

The measurement of the topological charges of a composite vortex beam is challenging. Therefore, this study proposes a method to detect the orbital angular momentum of each sub-beam using the light intensity distribution characteristics and diffraction patterns with an elliptical aperture occluding partial azimuth. Simulation results reveal that th...

The point spread function (PSF) plays a very important part in image post-processing and high-precion astrometry and photometry. It is necessary to analyse the properties of PSF before we use it to process data. However, in real observations, PSF is interfered by many different factors and the shape of it has inevitable spatial and temporal variati...

Telescopes with a wide field of view (greater than 1°) and small apertures (less than 2 m) are workhorses for observations such as sky surveys and fast-moving object detection, and play an important role in time-domain astronomy. However, images captured by these telescopes are contaminated by optical system aberrations, atmospheric turbulence, tra...

The beam carrying information will be affected by atmospheric turbulence as it propagates through the atmosphere. Under the modified Rytov method, using the non-Kolmogorov power spectrum, applying the atmospheric turbulent inner scale and the outer scale which changes with altitude, this paper obtained the expression of the spiral spectrum of the b...

This paper reports the realization of a closed-loop feedback system, which consists of a spatial light modulator controlled by the holographic tandem method, for adaptive far-field flattop beam shaping. The holographic tandem method iteratively adjusts the phase distributions to be written into the two different regions of a spatial light modulator...

The generation of atmosphere turbulence wave-front is important for studying the light propagation and imaging through the atmosphere, and correcting the atmosphere turbulence, such as the adaptive optics system. The power spectral density method generates phase screens quickly for using the fast Fourier transform (FFT). The main drawback to this a...

High fidelity Monte Carlo simulation of atmospheric turbulence phase screens is important for performance testing of astronomical adaptive optics systems. With a sparse spectrum model and an optimal sampling method, it is possible to generate an atmospheric turbulence phase screen with high fidelity. However, the phase screen generation speed is li...

As the pupil size of ground-based telescopes increases, adaptive optics systems become more and more important for almost all astronomical observations. To test the performance of adaptive optics systems through simulation and with test bench experiments, we need to model the atmospheric turbulence with high fidelity. To fulfil this goal, a new met...

The Shack-Hartmann wavefront sensor is widely used to measure aberrations induced by atmospheric turbulence in adaptive optics systems. However if there exists strong atmospheric turbulence or the brightness of guide stars is low, the accuracy of wavefront measurements will be affected. In this paper, we propose a compressive Shack-Hartmann wavefro...

A parallel blind deconvolution algorithm is presented. The algorithm contains the constraints of the point spread function (PSF) derived from the physical process of the imaging. Additionally, in order to obtain an effective restored image, the fractal energy ratio is used as an evaluation criterion to estimate the quality of the image. This algori...

MEMS deformable mirrors (DM) have many merits of low drive voltage, high response speed, small power consumption, low cost and small size. Its surface shape and displacement versus applied voltage are significant factors of MEMS DM. Phase-shifting interferometer (PSI) has many advantages such as non-contact, quickness and high precision. A phase-on...

Liquid crystal spatial light modulator (LC-SLM) has a series of attractive characteristics as a wavefront corrector in adaptive optics system such as compactness, high density integration, low cost and possibility of batch production. However it also suffers from several drawbacks such as low light efficiency. We present an analysis of the light ef...

The micro-lens array is the core component of Shack-Hartmann wavefront sensor. According to the phase modulation principle of liquid crystal spatial light modulator (LC-SLM), the LC-SLM generates dynamic micro-lens array with tunable focal length, aperture size, and arrangement of sub-apertures. Hartmann wavefront sensor based LC-SLM is used to spl...

Micro electro mechanical system (MEMS) deformable mirrors fabricated by surface technics have the advantages of small volume, high resolution and low driving voltage et al.. However a large number of etch holes on the mirror formed in a regular array structure affect the optical properties of the deformable mirror (DM). We design and manufacture ME...

Based on power spectral density method, the uniform sampling leading to the leakage of low frequency in atmosphere phase screens is analyzed. A new method - non-uniform sampling is proposed. The non-uniform sampling is modeled. The covered sampling frequency regions and the powers of single sampling region by the two sampling methods are discussed...

Partial coherence (generally represented by sigma) is one of the important parameters of lithographic tool to assess the performance of pupil fill. In this paper, a novel method of partial coherence measurement for the illumination system is proposed. Statistical results of measured sigma by the proposed method are analyzed. The dependence of parti...

A kind of diffractive pyramid wavefront sensor for the measurement of wavefront aberration is designed based on the refractive pyramid wavefront sensor and the binary optical principle. The theoretical derivation of diffractive pyramid wavefront detection is made and the intensity distribution of the four sub-pupil image for the single term Zernike...

Based on the theory of optical wave propagation in the slant path and the ITU-R atmospheric refractive index structure constant model which depends on the altitude, and considering the influence of inner scale, we studies the scintillation index from the transmitter to the target and that from the target to the receiver by using the modified Hill s...

Phase screen can reflect the change of refractive index correctly. Constructing an accurate atmospheric turbulence phase screen with small calculation amount is the key of numerical simulation. According to the statistical characteristics of turbulence, square atmospheric turbulence phase screen is calculated using fractal model. The simulation res...

Wave-front sensor, as the main component of Adaptive optics system, detects light from the astronomic object or reference sources. It aims to improve the utilization of light, especially for AO system work with the faint objects. Compared with Shack-Hartmann sensor, pyramid wave-front sensor is a relatively new one with increased pupil sampling and...

A new pyramid wavefront sensor (PWFS), which utilizes a reflective pyramid mirror instead of a refractive pyramid prism at the focus of a telescope, is presented. As a key optical component in this PWFS, the pyramid mirror requires accurate microfabrication for excellent quality of the tip, the turned edges, and the surfaces. The moving mask lithog...

The paper presents a closed-loop adaptive optics (AO) system that uses two deformable mirrors (DMs) to compensate for both amplitude and phase fluctuation of output beam. The validation and feasibility of an AO technology using two DMs has been verified experimentally. Consequently, the quality of laser beam in the near field is improved and the fa...

Based on conventional GS algorithm, an accuracy and fast algorithm for phase retrieval is presented. This algorithm, which can be called the accelerated angular spectrum iterative approad, induces a gradient by using the angular transfer functions. The intensity distribution of three planes, e.g. an incident plane and two emergent planes, is employ...

We design a dual axis rotary mirror based on microelectromechanical system technology used for the endoscopic optical coherence tomography (OCT) application. With the inherent advantages of the micromachined device such as small size, low consumption and high reliability, it allows the miniaturization of conventional bulky OCT probe. The dimension...

is paper demonstrates a 2D (two-dimensional) electrostatic MEMS scanning mirror. This scanner rotates on both axis X and Y, giving a two degrees of freedom. Finite element analysis has shown that optical scanning angle on axis X is 5.0° at 120V and axis Y is 4.4°at 160V. The structure has been optimized to achieve good dynamic performance.

For many astronomical systems, Adaptive Optics (AO) plays an important role. Here, we report some preliminary studies on MEMS (Micro-Electro-Mechanical-System) Project for micro actuators in AO applications at the Institute of Optics and Electronics, Chinese Academy of Science. This paper presents a few MEMS actuators based on repulsive electrostat...

A homogeneous aligned nematic liquid crystal (LC) cell can be used to phase modulate light. It has a series of attractive characteristics of compactness, high density integration, low cost and possibility of batch production in adaptive optics. However a problem has long existed for such devices is that they may be used only to control the phase of...

MEMS deformable mirror (DM) has yet to be incorporated into a facility AO instrument especially for atmospheric compensation. Apart from these drawbacks such as limited stroke, reliability, its optical efficiency should also be concerted. The wavefront corrector in AO system should existing high optical efficiency especially atmospheric compensatio...

Liquid-crystal spatial light modulator (LC-SLM) has the attractive advantages of large number of correcting elements, low applied voltage, easy control and low cost etc. as an emerging wave-front corrector. Based on the investigation of its time-space characteristics, the capability and limitations of LC-SLM in adaptive astronomical imaging applica...

The reflective liquid crystal on silicon-based display panel is used to compensate the human eye aberrations. And its characteristic of optical modulation is analyzed theoretically. A phase-mostly modulation can be achieved by proper parameters. An adaptive optical system is fabricated using LCOS as wavefront corrector and H-S sensor as wavefront s...

The adaptive optics (AO) technique without a wave-front sensor can optimize the system performance directly, while being independent of wave-front sensor. Based on stochastic parallel gradient descent (SPGD) control algorithm, an adaptive optics test-bed without a wave-front sensor was built with a 32-element deformable mirror and a CCD. Experiment...

A liquid-crystal spatial light modulator (LC-SLM) can be used to deflect laser beam, however its pixel structure and diffraction effect resulted from phase wrapping technique decreases its optical efficiency. The diffraction effect was analyzed theoretically and experimentally, and the relationship between fill factor and diffraction efficiency was...

The liquid crystal spatial light modulators (LC-SLM) are recently emerging as wavefront aberration correctors for use in low cost adaptive optics system (AO). As a novel aberration corrector, the wavefront generation performance of a phase-only LC-SLM is a governing factor that determines its ability for wave-front correction in an AO system. In th...

Optimizing the system performance metric directly is an important method for correcting wave-front distortions in adaptive optics(AO) systems. Appropriate stochastic parallel optimization control algorithm is the key to correcting distorted wave front successfully. Based on several stochastic parallel optimization control algorithms, an adaptive op...

The spatial and temporal characteristics of Modal P256 Liquid-crystal Spatial Light Modulator (LC-SLM) fabricated by Boulder Nonlinear System were investigated. A Michelson interferometer was conducted to test the phase of wave front using the LC-SLM as a reflective mirror. The phases generated by each pixel were different under the same gray value...

Liquid crystal spatial light modulator (LC-SLM) has a series of attractive characteristics as a wave-front corrector of adaptive optical system such as compactness, high density integration, low cost and possibility of batch production. However, it also has some limitations such as effective only on polarized light, chromatic aberration and low res...

For some adaptive optics (AO) systems, one deformable mirror (DM) can not meet the need of large stroke and high spatial frequency. In this paper, a double DMs way is present. In this system, a large stroke DM (LSDM) with low spatial frequency corrects low order aberrations and a high spatial frequency DM (HSFDM) with small stroke corrects high ord...