Laboratory demonstration of the prediction of wind-blown turbulence by adaptive optics at 8 kHz with use of LQG control.

The low-latency adaptive optical mirror system (LLAMAS) is designed to push the limits on achievable latencies and frame rates. It has 21 subapertures across its pupil. A reformulated version of the linear quadratic Gaussian (LQG) method predictive Fourier control is implemented in LLAMAS; for all modes, it takes just 30 µs to compute.

Wavefront shaping with a Hadamard basis for scattering soil imaging.

Soil is a scattering medium that inhibits imaging of plant-microbial-mineral interactions that are essential to plant health and soil carbon sequestration. However, optical imaging in the complex medium of soil has been stymied by the seemingly intractable problems of scattering and contrast. Here, we develop a wavefront shaping method based on adaptive stochastic parallel gradient descent optimization with a Hadamard basis to focus light through soil mineral samples.

X-ray metrology and performance of a 45-cm long x-ray deformable mirror.

We describe experiments with a 45-cm long x-ray deformable mirror (XDM) that have been conducted in End Station 2, Beamline 5.3.1 at the Advanced Light Source.

Performance of the Gemini Planet Imager's adaptive optics system.

The Gemini Planet Imager's adaptive optics (AO) subsystem was designed specifically to facilitate high-contrast imaging. A definitive description of the system's algorithms and technologies as built is given. 564 AO telemetry measurements from the Gemini Planet Imager Exoplanet Survey campaign are analyzed.

Computationally efficient autoregressive method for generating phase screens with frozen flow and turbulence in optical simulations.

We present a sample-based, autoregressive (AR) method for the generation and time evolution of atmospheric phase screens that is computationally efficient and uses a single parameter per Fourier mode to vary the power contained in the frozen flow and stochastic components. We address limitations of Fourier-based methods such as screen periodicity and low spatial frequency power content. Comparisons of adaptive optics (AO) simulator performance when fed AR phase screens and translating phase screens reveal significantly elevated residual closed-loop temporal power for small increases in added stochastic content at each time step, thus displaying the importance of properly modeling atmospheric "boiling".

Sub-nanometer flattening of 45 cm long, 45 actuator x-ray deformable mirror.

We have built a 45 cm long x-ray deformable mirror (XDM) of super-polished single-crystal silicon that has 45 actuators along the tangential axis. After assembly, the surface height error was 19 nm rms. With use of high-precision visible-light metrology and precise control algorithms, we have actuated the XDM and flattened its entire surface to 0.

Computer vision applications for coronagraphic optical alignment and image processing.

Modern coronagraphic systems require very precise alignment between optical components and can benefit greatly from automated image processing. We discuss three techniques commonly employed in the fields of computer vision and image analysis as applied to the Gemini Planet Imager, a new facility instrument for the Gemini South Observatory. We describe how feature extraction and clustering methods can be used to aid in automated system alignment tasks, and also present a search algorithm for finding regular features in science images used for calibration and data processing.

Kalman filtering to suppress spurious signals in adaptive optics control.

In many scenarios, an adaptive optics (AO) control system operates in the presence of temporally non-white noise. We use a Kalman filter with a state space formulation that allows suppression of this colored noise, hence improving residual error over the case where the noise is assumed to be white. We demonstrate the effectiveness of this new filter in the case of the estimated Gemini Planet Imager tip-tilt environment, where there are both common-path and non-common-path vibrations.

Laboratory demonstration of accurate and efficient nanometer-level wavefront control for extreme adaptive optics.

A 32 x 32 microelectricalmechanical systems mirror is controlled in a closed-loop adaptive optics test bed with a spatially filtered wavefront sensor (WFS), Fourier transform wavefront reconstruction, and calibration of references with a high-precision interferometer. When correcting the inherent aberration of the mirror, 0.7 nm rms phase error in the controllable band is achieved.

Fourier transform wavefront control with adaptive prediction of the atmosphere.

Predictive Fourier control is a temporal power spectral density-based adaptive method for adaptive optics that predicts the atmosphere under the assumption of frozen flow. The predictive controller is based on Kalman filtering and a Fourier decomposition of atmospheric turbulence using the Fourier transform reconstructor. It provides a stable way to compensate for arbitrary numbers of atmospheric layers.

Optimal Fourier control performance and speckle behavior in high-contrast imaging with adaptive optics.

High-contrast imaging with adaptive optics (AO) for planet detection requires a sophisticated AO control system to provide the best possible performance. We evaluate the performance improvements in terms of residual error and point-spread function intensity provided by optimal Fourier control using detailed end-to-end simulation. Intensity, however, is not the final measure of system performance.

Experimental demonstration of phase correction with a 32 x 32 microelectromechanical systems mirror and a spatially filtered wavefront sensor.

A 32 x 32 microelectromechanical systems deformable mirror is controlled in closed loop with a spatially filtered Shack-Hartmann wavefront sensor and a Fourier-transform wavefront reconstruction algorithm. A phase plate based on atmospheric turbulence statistics is used to generate a 1 microm peak-valley static phase aberration. Far-field images and direct phase measurements of the residual are used to compare performance with and without the spatial filter.

Optimal modal fourier-transform wavefront control.

Optimal modal Fourier-transform wavefront control combines the speed of Fourier-transform reconstruction (FTR) with real-time optimization of modal gains to form a fast, adaptive wavefront control scheme. Our modal basis is the real Fourier basis, which allows direct control of specific regions of the point-spread function. We formulate FTR as modal control and show how to measure custom filters.

Spatially filtered wave-front sensor for high-order adaptive optics.

Adaptive optics (AO) systems take sampled measurements of the wave-front phase. Because in the general case the spatial-frequency content of the phase aberration is not band limited, aliasing will occur. This aliasing will cause increased residual error and increased scattered light in the point-spread function (PSF).

Scene-based Shack-Hartmann wave-front sensing: analysis and simulation.

In many situations it is not possible for an adaptive optics system to use a point source to measure the phase derivative, such as imaging along slant paths through the atmosphere and observation of the earth from space with a lightweight optic. Instead, small subimages of the observed scene can be used in a scene-based wave-front sensing technique. This study presents three important advances in the understanding of this technique.

Experimental validation of Fourier-transform wave-front reconstruction at the Palomar Observatory.

Wave-front reconstruction with use of the Fourier transform has been validated through theory and simulation. This method provides a dramatic reduction in computational costs for large adaptive (AO) systems. Because such a reconstructor can be expressed as a matrix, it can be used as an alternative in a matrix-based AO control system.

Fast wave-front reconstruction in large adaptive optics systems with use of the Fourier transform.

Wave-front reconstruction with the use of the fast Fourier transform (FFT) and spatial filtering is shown to be computationally tractable and sufficiently accurate for use in large Shack-Hartmann-based adaptive optics systems (up to at least 10,000 actuators). This method is significantly faster than, and can have noise propagation comparable with that of, traditional vector-matrix-multiply reconstructors. The boundary problem that prevented the accurate reconstruction of phase in circular apertures by means of square-grid Fourier transforms (FTs) is identified and solved.