Linhai Huang

Modified Gaussian influence function of deformable mirror actuators.

A new deformable mirror influence function based on a Gaussian function is introduced to analyze the fitting capability of a deformable mirror. The modified expressions for both azimuthal and radial directions are presented based on the analysis of the residual error between a measured influence function and a Gaussian influence function. With a simplex search method, we further compare the fitting capability of our proposed influence function to fit the data produced by a Zygo interferometer with that of a Gaussian influence function. The result indicates that the modified Gaussian influence function provides much better performance in data fitting.

A single-shot common-path phase-stepping radial shearing interferometer for wavefront measurements

A single-shot common-path phase-stepping radial shearing interferometer (RSI) is proposed for wavefront measurements. In the proposed RSI, three quarter-wave plates are used as phase shifters to produce four spatially separated phase-stepping fringe patterns that are recorded simultaneously by a single CCD camera. The proposed RSI can measure the wavefront under test in real-time, and it is also insensitive to environmental vibration due to its common-path structure. Experimentally the proposed RSI is applied to detect the distorted wavefronts generated by a liquid crystal spatial light modulator. The measured aberrations are in good agreement with that obtained with (by) a Hartmann-Shack wavefront sensor, indicating that the proposed RSI is a useful tool for wavefront measurements.

Modal wavefront reconstruction for radial shearing interferometer with lateral shear

In a radial shearing interferometer, a portion of the test beam is magnified and used as the reference for the tested wavefront. However, the reference portion is always off center (lateral shear), which complicates the wavefront reconstruction. A modal method for solving this problem is presented here. This method uses orthogonal Zernike polynomials and its matrix formalism to calculate the Zernike coefficient of the wavefront under test. This approach has easier implementation, is better filtering, and has a more adaptive practical situation. The corresponding mathematical formula is deduced, and a computer simulation is also made to verify operation of the algorithm. The result of simulation analysis shows that the proposed method is correct and accurate.

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. The experimental results show that the measurement ability of G-PD WFS is improved obviously, especially for the wavefront aberration with larger amplitude.

Comparison between non-modulation four-sided and two-sided pyramid wavefront sensor

Based on the diffraction theory the paper analyzes non-modulation Pyramid wavefront sensor (PWFS, namely, four-sided pyramid) and two-sided pyramid wavefront sensor (TSPWFS), and expresses the detected signals as a function of the measured wavefront. The expressions of the detected signals show that non-modulation PWFS and TSPWFS hold the same properties of both slope and direct phase sensors. We compare both sensors working in slope and phase sensing by theory and numerical simulations. The results demonstrate that the performance of TSPWFS excels that of PWFS. Additionally, the influence of interference between adjacent pupils is discussed.

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. We also present an approach to extract the wavefront under test with random phase shift, which dramatically reduces the machining difficulty of the MRA. The feasibility and accuracy of the proposed method are further validated through our numerical analysis. With the advantages of vibration immunity, simultaneous phase stepping, and broad spectral range, the presented interferometer is expected to be of potential use in a variety of applications, such as the detection of moving objects and dynamic processes.

Co-phasing Measurement for Segmented Mirrors and Image Retrieval Technology Based on Phase Diversity

In order to improve the imaging resolution of a segmented telescope, the co-phasing error of segmented mirrors must be accurately measured and corrected. Phase Diversity (PD) refers to a technique of image-based wavefront sensing, and it could estimate both the unknown phase parameters and the unknown object. In this paper, the Phase diversity is proposed to measure the co-phasing errors and retrieve the unknown object for segmented mirrors, and the performance of this technique is simulated for point source and extended source. The simulation results demonstrate that the Phase Diversity Wavefront Sensor (PD WFS) can synchronously measure the piston errors of multi-segmented mirrors and the quality of the retrieved image is much better than before. The Phase Diversity Wavefront Sensor can be used to measure the co-phasing errors and retrieve the unknown object for the segmented mirror system.

Measurement method of the misalignment between the Hartmann-Shack sensor and the deformable mirror in an adaptive optics system

Misalignment between the Hartmann-Shack wavefront sensor (HSWFS) and the deformable mirror (DM) will degrade the performance of an adaptive optics (AO) system severely. In this paper, a method of measuring the misalignment between the HSWFS and the DM, which is called the marked actuators of the DM, is presented. The misalignments are divided into different groups and analyzed theoretically. In addition, a 45-element adaptive optics system is constructed to validate the accuracy of the method experimentally. As a consequence, the experimental result agrees well with the theoretical ones.

Closed-loop experiment of two deformable mirrors adaptive optics system compensating for amplitude and phase fluctuations

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 far field image is close to diffraction limit in the experiment. The Strehl ratio (SR) of far-field image increases from 0.837 using conventional AO technology to 0.952 using the two DMs AO technology.