Real-time wavefront correction using diffractive optical networks.

Real-time wavefront correction is a challenging problem to present for conventional adaptive optics systems. Here, we present an all-optical system to realize real-time wavefront correction. Using deep learning, the system, which contains only multiple transmissive diffractive layers, is trained to realize high-quality imaging for unknown, random, distorted wavefronts. Once physically fabricated, this passive optical system is physically positioned between the imaging lens and the image plane to all-optically correct unknown, new wavefronts whose wavefront errors are within the training range. Simulated experiments showed that the system designed for the on-axis field of view increases the average imaging Strehl Ratio from 0.32 to 0.94, and the other system intended for multiple fields of view increases the resolvable probability of binary stars from 30.5% to 69.5%. Results suggested that DAOS performed well when performing wavefront correction at the speed of light. The solution of real-time wavefront correction can be applied to other wavelengths and has great application potential in astronomical observation, laser communication, and other fields.

Overview of the LAMOST survey in the first decade.

The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST), also known as the Guoshoujing Telescope, is a major national scientific facility for astronomical research located in Xinglong, China. Beginning with a pilot survey in 2011, LAMOST has been surveying the night sky for more than 10 years. The LAMOST survey covers various objects in the Universe, from normal stars to peculiar ones, from the Milky Way to other galaxies, and from stellar black holes and their companions to quasars that ignite ancient galaxies. Until the latest data release 8, the LAMOST survey has released spectra for more than 10 million stars, ∼220,000 galaxies, and ∼71,000 quasars. With this largest celestial spectra database ever constructed, LAMOST has helped astronomers to deepen their understanding of the Universe, especially for our Milky Way galaxy and the millions of stars within it. In this article, we briefly review the characteristics, observations, and scientific achievements of LAMOST. In particular, we show how astrophysical knowledge about the Milky Way has been improved by LAMOST data.

Optical observations of LIGO source GW 170817 by the Antarctic Survey Telescopes at Dome A, Antarctica.

The LIGO detection of gravitational waves (GW) from merging black holes in 2015 marked the beginning of a new era in observational astronomy. The detection of an electromagnetic signal from a GW source is the critical next step to explore in detail the physics involved. The Antarctic Survey Telescopes (AST3), located at Dome A, Antarctica, is uniquely situated for rapid response time-domain astronomy with its continuous night-time coverage during the austral winter. We report optical observations of the GW source (GW 170817) in the nearby galaxy NGC 4993 using AST3. The data show a rapidly fading transient at around 1 day after the GW trigger, with the i-band magnitude declining from 17.23±0.13 magnitude to 17.72±0.09 magnitude in ~1.8 h. The brightness and time evolution of the optical transient associated with GW 170817 are broadly consistent with the predictions of models involving merging binary neutron stars. We infer from our data that the merging process ejected about ∼10-2 solar mass of radioactive material at a speed of up to 30% the speed of light.

Large field-of-view Fourier transform imaging spectrometer using dual-channel stitching.

A dual-channel lateral shearing beam splitter was used in a Fourier transform imaging spectrometer, forming a dual-channel imaging spectrometer, to investigate the usability of this technique for large field-of-view (FOV) spectral detection. The large FOV obtained by stitching together the different channels' individual FOVs greatly improved the spectral detection efficiency for large-area targets. This report describes the principle of the dual-rectangle lateral shearing beam splitter and the analysis of the lateral shearing distance, FOV, modulation, and method of dual-channel stitching. Large-FOV spectral images of a scene were acquired experimentally at visible wavelengths, confirming the effectiveness of this technique.

Curvature wavefront sensing based on a single defocused image and intensity compensation.

Curvature wavefront sensing usually requires the measurement of two defocused images at equal distances before and after the focus. In this paper, a new wavefront recovery algorithm based on only one defocused image is proposed. This algorithm contains the following four steps: response matrix calculation, establishment of intensity distribution equations, Zernike coefficients solution derived from the least squares method, and defocused image compensation with the solved Zernike coefficients. The performance of the algorithm in a large obscuration ratio and fast focal ratio optical system on axis and the edge of the field of view (FOV) is examined. Two optical systems of the Hubble telescope and a modified Paul-Baker telescope are employed to test the algorithm. The simulations show that the proposed algorithm outperforms in structural simplicity, and applications are expected in the wavefront recovery of the extreme environment (i.e., in space and the Antarctic).

Measuring seeing with a Shack-Hartmann wave-front sensor during an active-optics experiment.

We describe the measurement of atmospheric enclosure seeing along a 120-m light path by use of a Shack-Hartmann wave-front sensor (S-H WFS) for the first time to our knowledge in the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) outdoor active-optics experiment system, based on the differential image motion method and a S-H WFS. Seeing estimates that were gained with the S-H WFS were analyzed and found to be in close agreement with the actual seeing conditions, the estimates of refractive-index structure constant, and the thin-mirror active optics results, which usually include the shape sensing precision and the active correction precision of the experimental system. Finally, some countermeasures against poor seeing conditions were considered and adopted.