Phase unwrapping algorithm based on phase diversity wavefront reconstruction and virtual Hartmann-Shack technology.

Phase unwrapping (PU) algorithms play a crucial role in various phase measurement techniques. Traditional algorithms cannot work well in strong noise environments, which makes it very difficult to obtain the accurate absolute phase from the noisy wrapped phase. In this Letter, we introduce a novel, to the best of our knowledge, phase unwrapping algorithm named PD-VHS.

Performance evaluation of ground layer adaptive optics based on layer correction efficiency.

Ground layer adaptive optics (GLAO) has been widely employed in wide-field observations with ground-based telescopes. However, the present evaluation of GLAO performance lacks a criterion in terms of turbulence layer correction. This deficiency results in a significant gap in understanding the effectiveness of GLAO correction at different heights of the turbulence layer, thereby hindering the optimization of GLAO system performance.

No-Reference Quality Assessment of Extended Target Adaptive Optics Images Using Deep Neural Network.

This paper proposes a supervised deep neural network model for accomplishing highly efficient image quality assessment (IQA) for adaptive optics (AO) images. The AO imaging systems based on ground-based telescopes suffer from residual atmospheric turbulence, tracking error, and photoelectric noise, which can lead to varying degrees of image degradation, making image processing challenging. Currently, assessing the quality and selecting frames of AO images depend on either traditional IQA methods or manual evaluation by experienced researchers, neither of which is entirely reliable.

MWDNs: reconstruction in multi-scale feature spaces for lensless imaging.

Lensless cameras, consisting of only a sensor and a mask, are small and flexible enough to be used in many applications with stringent scale constraints. These mask-based imagers encode scenes in caustic patterns. Most existing reconstruction algorithms rely on multiple iterations based on physical model for deconvolution followed by deep learning for perception, among which the main limitation of reconstruction quality is the mismatch between the ideal and the real model.

Dispersed fringe cophasing method based on principal component analysis.

With the success of the Webb telescope, dispersed fringe sensing (DFS), with the significant merit of a large capture range, is proving to be a promising cophasing approach for a large-aperture segmented telescope. In this Letter, a novel, to the best of our knowledge, piston error extraction method based on principal component analysis (PCA) technology is proposed. In this method, all the one-dimension intensity distributions along the dispersion axis for different interference positions are regarded as a set of random phase-shifted interference signals.

Region-correlation algorithm with improved dynamic range and reconstruction accuracy for extended object wavefront sensing.

The correlation Shack-Hartmann wavefront sensor (SHWFS) is widely used in many fields in addition to solar adaptive optics. The requirement for the SHWFS dynamic range increases with the diameter of the telescope, which means a larger detector array is needed. However, the size of the detector would be restricted by the high frame rate needed for the solar observation.

Analytical calibration of slope response of Zernike modes in a Shack-Hartmann wavefront sensor based on matrix product.

The Shack-Hartmann wavefront sensor (SH-WFS) is widely used as a slope-based wavefront sensing device. The modal method is favored for wavefront reconstruction from SH-WFS output because of its excellent performance. In this case, the calibration of modal (commonly Zernike modes) slope is required in advance.

Polarization imaging based on time-integration by a continuous rotating polarizer.

Polarimeter by rotating polarizer is one of the well-known and classic division of time polarimeter (DoTP). It is generally acknowledged that this kind of polarimeter is time consuming for each measurement although it has simple, accurate and compact performances. In this paper we present a time-integration polarimeter by using a continuous rotating polarizer.

Constrained least-squares algorithm for active optics correction of a primary mirror.

Active optics technology improves the performance and image quality of large telescopes. To effectively compensate for optical aberrations, the constrained least-squares (CLS) algorithm, which considers the characteristics of the resultant moment, the force budget, and the local force smoothness, is proposed to optimize the force distribution. First, the constraint of the resultant moment is used to decouple the shape control and location control.

Unified analytical method for Zernike coefficient transformation of scaled, rotated, and translated pupils based on Shack's vector multiplication.

Zernike polynomials play an essential role in characterizing and analyzing wavefront aberrations. Transformation of weighted coefficients for Zernike modes is required when pupil scaling, rotation, and/or translation exist. Here, a novel method based on Shack's vector multiplication is first proposed to derive the transformation relation.

Sub-Millisecond Phase Retrieval for Phase-Diversity Wavefront Sensor.

We propose a convolutional neural network (CNN) based method, namely phase diversity convolutional neural network (PD-CNN) for the speed acceleration of phase-diversity wavefront sensing. The PD-CNN has achieved a state-of-the-art result, with the inference speed about 0.5 ms, while fusing the information of the focal and defocused intensity images.

Dispersed-fringe-accumulation-based left-subtract-right method for fine co-phasing of a dispersed fringe sensor.

In this paper, a dispersed-fringe-accumulation (DFA)-based left-subtract-right (LSR) piston estimation method (DFA-LSR), in which the dispersed fringe image is accumulated in the dispersed direction, and then the LSR method is used to estimate the piston error, is proposed for dispersed fringe sensors (DFS) in the fine co-phasing stage. The DFS is usually used to detect the piston errors (optical path difference) between different segmented mirrors or synthetic aperture telescopes. The DFA-LSR makes up for the shortcomings of the main peak position (MPP) method, which suffers from the constant offset in the pixel counts.

Compact single-shot radial shearing interferometer with random phase shift.

We propose a compact phase-shifting radial shearing interferometer based on a pixelated micro-retarder array (MRA). The MRA is made of a thin birefringence plate, and is composed of identical units that have pixels of four different thicknesses. We demonstrate that pixelated phase delay between two shearing beams can be introduced by applying the fast axis of birefringence plate in the horizontal or vertical orientation.

Solar multi-conjugate adaptive optics based on high order ground layer adaptive optics and low order high altitude correction.

Multi-conjugate adaptive optics (MCAO) is the most promising technique currently developed to enlarge the corrected field of view of adaptive optics for astronomy. In this paper, we propose a new configuration of solar MCAO based on high order ground layer adaptive optics and low order high altitude correction, which result in a homogeneous correction effect in the whole field of view. An individual high order multiple direction Shack-Hartmann wavefront sensor is employed in the configuration to detect the ground layer turbulence for low altitude correction.

First on-sky demonstration of the piezoelectric adaptive secondary mirror.

We propose using a piezoelectric adaptive secondary mirror (PASM) in the medium-sized adaptive telescopes with a 2-4 m aperture for structure and control simplification by utilizing the piezoelectric actuators in contrast with the voice-coil adaptive secondary mirror. A closed-loop experimental setup was built for on-sky demonstration of the 73-element PASM developed by our laboratory. In this Letter, the PASM and the closed-loop adaptive optics system are introduced.

[The Aberration Corrected Grating Spectrometer Based on Adaptive Optics].

To study the thermodynamics properties of the solar atmosphere with different height distribution, the imaging grating spectrometer with excellent image quality is one of the important tools to achieve this goal. However, the atmosphere turbulence can not be avoided for the imaging grating spectrometer installed in the ground-based solar telescope, and the imaging properties of the grating spectrometer will influenced by the wavefront aberration generalized by the atmosphere turbulence and the wavefront aberration generalized by the optical system adjusting errors and the optical element manufacturing errors. The atmospheric turbulence can be effectively compensated by the Adaptive Optics.

Heat-stop structure design with high cooling efficiency for large ground-based solar telescope.

A heat-stop is one of the most important thermal control devices for a large ground-based solar telescope. For controlling the internal seeing effect, the temperature difference between the heat-stop and the ambient environment needs to be reduced, and a heat-stop with high cooling efficiency is required. In this paper, a novel design concept for the heat-stop, in which a multichannel loop cooling system is utilized to obtain higher cooling efficiency, is proposed.

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

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.

Speckle image reconstruction of the adaptive optics solar images.

Speckle image reconstruction, in which the speckle transfer function (STF) is modeled as annular distribution according to the angular dependence of adaptive optics (AO) compensation and the individual STF in each annulus is obtained by the corresponding Fried parameter calculated from the traditional spectral ratio method, is used to restore the solar images corrected by AO system in this paper. The reconstructions of the solar images acquired by a 37-element AO system validate this method and the image quality is improved evidently. Moreover, we found the photometric accuracy of the reconstruction is field dependent due to the influence of AO correction.

Speckle transfer function for partial correction adaptive optics image reconstruction.

The residual aberrations of adaptive optics (AO) images can be removed by the speckle reconstruction method. To achieve accurate photometry, the knowledge of the speckle transfer function (STF) is necessary. In this Letter, a new method is proposed to evaluate the STF for speckle image reconstruction based on the partial correction AO.

Extension of the modal wave-front reconstruction algorithm to non-uniform illumination.

Attempts are made to eliminate the effects of non-uniform illumination on the precision of wave-front measurement. To achieve this, the relationship between the wave-front slope at a single sub-aperture and the distributions of the phase and light intensity of the wave-front were first analyzed to obtain the relevant theoretical formulae. Then, based on the principle of modal wave-front reconstruction, the influence of the light intensity distribution on the wave-front slope is introduced into the calculation of the reconstruction matrix.

Multichannel-Hadamard calibration of high-order adaptive optics systems.

we present a novel technique of calibrating the interaction matrix for high-order adaptive optics systems, called the multichannel-Hadamard method. In this method, the deformable mirror actuators are firstly divided into a series of channels according to their coupling relationship, and then the voltage-oriented Hadamard method is applied to these channels. Taking the 595-element adaptive optics system as an example, the procedure is described in detail.

Experimental study on modified linear quadratic Gaussian control for adaptive optics.

To achieve high-resolution imaging the standard control algorithm used for classical adaptive optics (AO) is the simple but efficient proportional-integral (PI) controller. The goal is to minimize the rms error of the residual wave front. However, using the PI controller, it is not possible to do this.

Error analysis of the de-crosstalk algorithm for the multianode-PMT-based quadrant tracking sensor.

For the multianode-PMT-based quadrant tracking sensor, one of the tracking error sources is the crosstalk. The crosstalk can be reduced by de-crosstalk algorithm, so the tracking error of the de-crosstalk algorithm for the multianode-PMT-based quadrant tracking sensor are analyzed in theory and verified by experiments. Both the theoretical analysis and the experimental results showed that the spot displacement sensitivity could be improved by the de-crosstalk algorithm, but the spot centroid detecting error increased at the same time.

Experimental study of a modified phase diversity with a diffraction grating.

The measurement ability of the conventional Phase diversity wavefront sensor (C-PD WFS) is limited by the accuracy and dynamic range of CCD cameras. In this letter, a modified Phase diversity wavefront sensor based on a diffraction grating (G-PD WFS) is proposed. We build a corresponding experimental setup to compare the measurement accuracy of the G-PD WFS and the C-GPDWFS under the same experimental conditions.