This PDF file contains the front matter associated with SPIE Proceedings Volume 7093, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing.

We introduce and demonstrate a compact, nonmechanical beam steering device based on liquid Crystal (LC) Polarization Gratings (PGs). Directional control of collimated light is essential for free-space optical communications, remote sensing, and related technologies. However, current beam steering methods often require moving parts, or are limited to small angle operation, offer low optical throughput, and are constrained by size and weight. We employ multiple layers of LCPGs to achieve wide-angle (> ±40°), coarse beam steering of 1550 nm light in a remarkably thin package. LCPGs can be made in switchable or polymer materials, and possess a continuous periodic birefringence profile, that renders several compelling properties (experimentally realized): ~ 100% experimental diffraction efficiency into a single order, high polarization sensitivity, and very low scattering. Light may be controlled within and between the zero- and first-diffraction orders by the handedness of the incident light and potentially by voltage applied to the PG itself. We implement a coarse steering device with several LCPGs matched with active halfwave LC variable retarders. Here, we present the preliminary experimental results and discuss the unique capability of this wide-angle steering.

The Naval Research Laboratory (NRL) has been conducting research in novel portable adaptive optics systems for many years. These systems are tested exhaustively in a laboratory environment before being migrated to field experiments on astronomical telescopes. As part of the laboratory testing, an atmosphere simulator hardware testbed has been developed to provide a realization of atmospheric turbulence based on Kolmogorov statistics. In this testbed, a high-pixel count liquid crystal spatial light modulator induces the atmospheric turbulence through a series of computer calculated phase maps. User controls allow a wide range of telescope apertures and seeing conditions to be explored for testing the adaptive optics system. This paper explains and reports on the use of this dynamic and expandable system in characterizing the performance and optimization parameters of the adaptive optics systems at NRL.

The Adaptive Optics Laboratory of the University of Victoria has built a LGS SH-WFS test bench for the Thirty-Meter- Telescope project and its AO system, NFIRAOS. The UVic AOLab has recently shown the ability to track Na profile induced aberrations while correcting for turbulence aberrations. The UVic AOLab has started the second phase of development of its LGS SH-WFS test bench. This next step consists of adding the Truth WFSs into the current bench design and of modeling and implementing the algorithms which blend the data coming from the variousWFSs. This paper shows the various components of the control architecture of NFIRAOS LGS wavefront sensing process. A first simulation shows the stability of the proposed control architecture and demonstrates that the DM is kept away from reproducing the LGS aberrations.

Previously, we demonstrated useful and novel features of the General Dynamics QuickStar adaptive-optics testbed utilizing Phase Diversity (PD) as the wavefront sensor operating on a point object. Point objects are relatively easy to produce in the laboratory and simplify the calibration procedure. However, for some applications, natural or artificial beacons may not be readily available and a wavefront sensor that operates on extended scenes is required. Accordingly, the QuickStar testbed has been augmented to allow PD to operate on natural three-dimensional solar-illuminated scenes external to the QuickStar laboratory. In addition, a computationally efficient chip-selection strategy has been developed that allows PD to operate on chips with favorable scene content. Finally, a covariance matrix has been developed that provides an accuracy estimate for PD wavefront-parameter estimates. The covariance can be used by the controls algorithm to properly weight the correction applied according to the accuracy of the estimates. These advances suggest that PD is a sufficiently mature technology for use in adaptive optics systems that require operation with extended scenes.

Laser beam shaping in far-field zone by means of liquid crystal modulator (LCM) and semipassive bimorph deformable mirror (SBDM) both placed in near-field is discussed. Phase delay of LCM and SBDM is calculated by means of Gerchberg-Saxton (GS) algorithm. The analysis of GS algorithm accuracy, convergence and stability is conducted; the influence of laser radiation characteristics, optical scheme parameters and initial phase estimation on algorithm performance is considered. Hybrid combination of Hill-climbing and GS algorithm is proposed for beam-shaping quality improvement. However, GS algorithm is known to fail in the case of multimode beam formation. To broaden the GS algorithm application area, we suggest the modification of the algorithm that makes possible not only single-mode beam shaping but also multimode one. The phase delay of LCM or SBDM is calculated as the sum of each mode phase multiplied by its relative intensity. Several practical examples of singlemode and multimode beam transformations are shown.

This is the first of two papers discussing aspects of placing the deformable mirror in a location not conjugate to the pupil plane of the telescope. The Starfire Optical Range, Air Force Research Laboratory's Directed Energy Directorate is in the process of developing a high efficiency AO system for its 3.5m optical telescope. The objective is to achieve maximum diffraction limited performance, i.e., largest pupil diameter possible, and maximum optical throughput. The later can be achieved by placing the deformable mirror outside the pupil. However placing the DM in a location not conjugate to the pupil results in a degradation in optical performance. This paper discusses experimental measurements of the degradation. In this paper we discuss the DM-not-in-pupil experimental testbed, the difficulties associated with creating this type of testbed, and how these difficulties were overcome. We also present results from the successful lab demonstration of closed loop performance with the DM placed out of pupil. We experimentally measured the degradation in Strehl and implemented a mitigation technique. Our experimental results indicate the mean degradation in Strehl as a result of placing the DM out of pupil to be between 7% and 9 %. This result is comparable with wave optics simulation and theoretical results which will be discussed in a companion paper, "Adaptive optics with DM not in pupil - Part 2: Mitigation of Degradation".

Metric adaptive optics systems search over a set of wavefront modes or commands to actuators to optimize a system performance metric like Strehl ratio or brightness. These systems have been explored for many decades and have been thought to be unreliable due to local minima in the metric space. It has been shown that some modes match well with no local minima to a given metric, but they rely on the ability of a mirror to create reliable replicas of the search modes. We present here a study of the most common implementation of metric adaptive optics that involves searching over the actuator command space while evaluating an intensity-based metric. We map an error space relating a common metric to actuator commands and statistically analyze the error function to determine the quantity and location of the local minima.

Optical interferometry, especially the lateral Shearing interferometer, has long played a role in wavefront sensing. Phase-Shifting Interferometry and also Self-Referencing Interferometry have significant advantages over the Shack-Hartmann wavefront sensor. Phase difference between two interfering beams is determined by measuring the intensity while the phase difference between the two interfering beams is changed in a known manner three times. The phase difference can then be determined in the presence of aberration. Adaptive wavelets will be applied to Phase-Shifting Interferometry in order to address both noise and coherence and increase the depth of fringes. Phase is determined by means of wavelet ridge extraction which will increase the depth of interference fringes and improve resolution.

Optical interferometry, especially the lateral Shearing interferometer, has long played a role in wavefront sensing. Phase-Shifting Interferometry and also Self-Referencing Interferometry have significant advantages over the Shack-Hartmann wavefront sensor. Phase difference between two interfering beams is determined by measuring the intensity while the phase difference between the two interfering beams is changed in a known manner three times. The phase difference can then be determined in the presence of aberration. Adaptive wavelets will be applied to Phase-Shifting Interferometry in order to address both noise and coherence and increase the depth of fringes. Phase is determined by means of wavelet ridge extraction which will increase the depth of interference fringes and improve resolution.

The Air Force Research Laboratory's (AFRL) Sodium Guidestar Adaptive Optics for Space Situational Awareness program (NGAS) sponsored research on spatially non-uniform gain for the servo-loop controller of an adaptive optics (AO) system. The edge subapertures of a Shack-Hartmann wavefront sensor have lower signalto- noise ratios and are more susceptible to measurement errors than fully illuminated center subapertures. These measurement errors produce errant commands over the corresponding edge actuators and can induce instabilities over these regions in strong turbulence conditions. The Non-uniform Gain Experiment (NUGE) concentrated on the development and experimental analysis of spatially varying gain maps on the servo-loop controller of a deformable mirror. The goal was to improve AO system performance and mitigate instabilities that can occur over the edge actuators of a deformable mirror. A gain map with a ring of lower filter gains b over just the outer actuators was experimentally shown to increase the overall Strehl ratio of the AO system in all of the tested turbulence conditions. A Gaussian gain map was also shown to significantly reduce the overall residual phase variance over the edge actuators thereby reducing the formation of the instabilities. Experiments were conducted at the Starfire Optical Range (SOR), AFRL, Kirtland AFB.

Recently, we reported an adaptive cross-correlation (ACC) algorithm to estimate with high accuracy the shift as large as several pixels between two extended-scene sub-images captured by a Shack-Hartmann wavefront sensor. It determines the positions of all extended-scene image cells relative to a reference cell in the same frame using an FFT-based iterative image-shifting algorithm. It works with both point-source spot images as well as extended scene images. We have demonstrated previously based on some measured images that the ACC algorithm can determine image shifts with as high an accuracy as 0.01 pixel for shifts as large 3 pixels, and yield similar results for both point source spot images and extended scene images. The shift estimate accuracy of the ACC algorithm depends on illumination level, background, and scene content in addition to the amount of the shift between two image cells. In this paper we investigate how the performance of the ACC algorithm depends on the quality and the frequency content of extended scene images captured by a Shack-Hatmann camera. We also compare the performance of the ACC algorithm with those of several other approaches, and introduce a failsafe criterion for the ACC algorithm-based extended scene Shack-Hatmann sensors.

The performance of laser machining systems can often be improved by adjusting the intensity profile of the beam on the target. Shaping a laser intensity profile can be efficiently accomplished by adjusting the spatial phase of the beam before propagating the beam a distance to the target. Beam shaping can be accomplished with passive diffractive elements, but this technique is only capable of creating a single intensity profile and is usually very sensitive to the input beam characteristics. Beam shaping with active optical elements like deformable mirrors can enable the system to achieve multiple shapes and compensate for non-ideal input beams, but can be very expensive. We present here a demonstration of laser beam shaping with low-cost membrane deformable mirrors.

Using a device to act as a surrogate for atmospheric turbulence in a laboratory is necessary to build and test optical systems for imaging, lidar, laser weapons, and laser communications. Liquid-crystal spatial light modulators (LC SLMs) and segmented micro-electro-mechanical-system (MEMS) deformable mirrors (DMs) are common devices for altering wavefronts to simulate a portion of atmospheric turbulence. The limitations of pixelation effects on a segmented wavefront control device were investigated theoretically. The results of this analysis were then verified by simulation. It was found that while LC SLMs with fine pixel resolution have almost no adverse effects from pixelation, segmented MEMS DMs have limitations related to the number of mirror segments on a DM. The performance capabilities of several available commercial devices are better understood as a result of this research.