This PDF file contains the front matter associated with SPIE Proceedings Volume 7931, including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

Development of space telescopes, such as the Hubble Space Telescope and the James Webb Telescope has been very challenging in terms of cost, schedule, and performance. For several future space missions, larger aperture and lightweight deployable mirrors, in the range of 10-20 meters in diameter with high surface accuracy, are required. In order to achieve lightweight, reduce cost for development and provide performance robustness, actuated hybrid mirror (AHM) technology is under development. The Naval Postgraduate School (NPS) recently received a 3-meter diameter space telescope testbed with six segments that uses an AHM technology. This paper will discuss the work performed at NPS on the surface control of the primary mirror using adaptive optics. This paper will also discuss how we can use a MEMS deformable mirror to improve the performance of the NPS segmented mirror telescope. The high-stroke, high-order actuated MEMS deformable mirror will correct the residual alignment and surface errors that are not corrected by the actuators on the mirrors. The mirror will use electrostatic actuation to eliminate the need for power to hold its position and will be capable of open-loop, go-to positioning.

We present our plans for a second-generation laser guide star adaptive optics system for the 3-meter Shane Telescope at Lick Observatory. The Shane hosted the first groundbreaking experiments in sodium laser guidestar adaptive optics, with observations starting in 1996, and provides for regular astronomical science observing to this day. The replacement new generation system will incorporate many of the recent advancements in AO technology and lessons learned from laboratory and on-sky experiments in order to provide higher Strehl, higher sensitivity, and greater wavelength coverage for astronomers. The proposed system uses a 32x32 actuator MEMS deformable mirror, along with higher sensitivity wavefront sensor, and a new fiber laser developed at Lawrence Livermore National Laboratory. Our experiences from the Villages project, reported at earlier Photonics West meetings, provide much of the basis for the new system design.

We briefly review the development history of the Gemini Planet Imager's 4K Boston Micromachines MEMS deformable mirror. We discuss essential calibration steps and algorithms to control the MEMS with nanometer precision, including voltage-phase calibration and influence function characterization. We discuss the integration of the MEMS into GPI's Adaptive Optics system at Lawrence Livermore and present experimental results of 1.5 kHz closed-loop control. We detail mitigation strategies in the coronagraph to reduce the impact of abnormal actuators on final image contrast.

For the past decade our group has been involved in the development and test of small portable Adaptive Optics (AO) systems based on MEMs Deformable Mirrors (DM) technology. The main trust of this activity was toward what is usually referred as vertical propagation of the light that is the common situation for astronomical applications. However, in the past couple of years our efforts have been towards the correction of horizontal path imagery. In this regime the atmospheric turbulence presents different types of problems such to make the development of AO systems much more demanding. Once again one of the starting points for us is the development of a test bed where AO components and algorithms can be tested under well controlled conditions.

Wide field of view (FOV) retinal imaging with high resolution has been demonstrated for quantitative analysis of retinal microstructures. An adaptive optics scanning laser ophthalmoscope (AO-SLO) that was built in our laboratory was improved by a customized scanning protocol for scanning wide region. A post-processing program was developed for generating wide FOV retinal images. The high resolution retinal image with 1.7 degree by 3.0 degree FOV were obtained.

We present a new type of unimorph deformable mirror with monolithic tip-tilt functionality. The tip-tilt actuation is based on a spiral arm design. The mirror will be used in high-power laser resonators for real-time intracavity phase control. The additional tip-tilt correction with a stroke up to 6 μm simplifies the resonator alignment significantly. The mirror is optimized for a laser beam footprint of about 10 mm. We have modeled and optimized this mirror by finite element calculations and we will present design criteria and tradeoffs for this mirrors. The mirror is manufactured from a super-polished glass substrate with very low surface scattering and excellent dielectric coating.

Iris AO is actively developing piston-tip-tilt (PTT) segmented MEMS deformable mirrors (DM) and adaptive optics (AO) controllers for these DMs. This paper discusses ongoing research at Iris AO that has advanced the state-of-the-art of these devices and systems over the past year. Improvements made to open-loop operation and mirror fabrication enables mirrors to open-loop flatten to 4 nm rms. Additional testing of an anti snap-in technology was conducted and demonstrates that the technology can withstand 100 million snap-in events without failure. Deformable mirrors with dielectric coatings are shown that are capable of handling 630 W/cm² of incident laser power. Over a localized region on the segment, the dielectric coatings can withstand 100kW/cm² incident laser power for 30 minutes. Results from the first-ever batch of PTT489 DMs that were shipped to pilot customers are reported. Optimizations made to the open-loop PTT controller are shown to have latencies of 157.5 μs and synchronous array update rates of nearly 6.5 kHz. Finally, plans for the design and fabrication of the next-generation PTT939 DM are presented.

The MEMS deformable mirror (DM) performances have been dramatically increased during the last years. Although adaptive optics has the potential to address many optical problems faced by engineers and scientists, it has not yet reached all domains of applications that it might reach. In this article, we present some key changes.

Adaptive optics for the next generation of extremely large telescopes (30 - 50 meter diameter primary mirrors) requires high-stroke (10 microns), high-order (100x100) deformable mirrors at lower-cost than current technology. Lowering the cost while improving the performance of deformable mirrors is possible using Micro-Electro-Mechanical Systems (MEMS) technology. In this paper the fabrication and testing of an array of high-stroke gold MEMS X-beam actuators attached to a continuous gold facesheet will be described. Both the actuator and the facesheet were fabricated monolithically in gold plated onto a thermally matched ceramic-glass substrate (WMS-15) using a high-aspect ratio fabrication process. Continuous facesheets that are deformed due to stress gradients have been annealed at high temperature and for an extended amount of time. The facesheet was flattened to the point where features such as etch holes and support post topography were easily distinguishable. Initial root-mean-square (RMS) topography at center of facesheet attached to a 16x16 X-beam actuator array with 1mm pitch was measured to be ~13.8μm. After annealing, the surface topography was measured to be ~1.0μm.

Step-structured thermo-mechanical actuators based on aluminum nitride (AlN) thin films and their application in refractive beam steering are investigated. The actuators will tilt a suspended plate and deform a liquid surface to realize a micro-prism. Arrays of tunable micro-prisms will increase the resolution of compound eye systems. A numerical actuator description is presented and the beam geometry is investigated, considering achievable tilt angles and actuator linearity. For an accurate design, the coefficient of thermal expansion (CTE) of AlN is determined, while measuring the bow of a coated silicon substrate at different temperatures. For a temperature difference of 300 K, the results show a maximum tilt angle of 7.1 °, which is independent of actuator length. Furthermore, the fabrication process is introduced and the nano-crystalline structure of AlN at facets, which are caused by pre-structured substrates, is investigated.

Adaptive optics (AO) systems are well demonstrated in the literature with both laboratory and real-world systems being developed. Some of these systems have employed MEMS deformable mirrors as their active corrective element. More recent work in AO for astronomical applications has focused on providing correction in more than one conjugate plane. Additionally, horizontal path AO systems are exploring correction in multiple conjugate planes. This provides challenges for a laboratory system as the aberrations need to be generated and corrected in more than one plane in the optical system. Our work with compact AO systems employing MEMS technology in addition to liquid crystal spatial light modulator (SLM) driven aberration generators has been scaled up to a two conjugate plane testbed. Using two SLM based aberration generators and two separate wavefront sensors, the system can apply correction with two MEMS deformable mirrors. The challenges in such a system are to properly match non-identical components and weight the correction algorithm for correcting in two planes. This paper demonstrates preliminary results and analysis with this system with wavefront data and residual error measurements.

A prototype optical system for compact, high-speed zooming is described. The system is enabled by a pair of MEMS deformable mirrors (DMs), and is capable of high-speed optical zoom without translation of components. We describe experiments conducted with the zoom system integrated with an optical microscope, demonstrating 2.5× zoom capability. Zoom is achieved by simultaneously adjusting focal lengths of the two DMs, which are inserted between an infinity-corrected microscope objective and a tube lens. In addition to zoom, the test system is demonstrated to be capable of automated fine focus control and adaptive aberration compensation. Image quality is measured using contrast modulation, and performance of the system is quantified.

It has now been widely demonstrated that AO can play a significant role in improving the image quality obtained in optical microscopes, in particular imaging deeply into biological samples. Although there are differences in the challenge of overcoming aberrations in optical microscopy and astronomy, for example effects are generally less dynamic in microscopy; there is a commonality in having to determine the shape to be placed on the adaptive optic element. This paper briefly reviews the in-depth imaging challenge and then present results on different approaches to determining the mirror shape and real-time closed loop control of AO in microscopy in both wide-field and beam scanning instruments.

Most implementations of adaptive optics in microscopes have not employed a wavefront sensor, but have instead used sensorless aberration correction methods. In these systems, the aberration is determined indirectly through the optimisation of a quality metric, such as image intensity. We explain the principles behind this approach and show how efficient correction schemes can be developed using suitable mathematical models. In particular, we explain how the correct choice of aberration expansion enables the independent measurement of each aberration mode via a simple quadratic maximisation.

Two-photon fluorescence microscopy provides a powerful tool for deep tissue imaging. However, optical aberrations from illumination beam path limit imaging depth and resolution. Adaptive Optics (AO) is found to be useful to compensate for optical aberrations and improve image resolution and contrast from two-photon excitation. We have developed an AO system relying on a MEMS Deformable Mirror (DM) to compensate the optical aberrations in a two-photon scanning laser fluorescence microscope. The AO system utilized a Zernike polynomial based stochastic parallel gradient descent (SPGD) algorithm to optimize the DM shape for wavefront correction. The developed microscope is applied for subsurface imaging of mouse bone marrow. It was demonstrated that AO allows 80% increase in fluorescence signal intensity from bone cavities 145um below the surface. The AO-enhanced microscope provides cellular level images of mouse bone marrow at depths exceeding those achievable without AO.

Inhomogeneous optical properties of biological samples make it difficult to obtain diffraction-limited resolution in depth. Correcting the sample-induced optical aberrations needs adaptive optics (AO). However, the direct wavefront-sensing approach commonly used in astronomy is not suitable for most biological samples due to their strong scattering of light. We developed an image-based AO approach that is insensitive to sample scattering. By comparing images of the sample taken with different segments of the pupil illuminated, local tilt in the wavefront is measured from image shift. The aberrated wavefront is then obtained either by measuring the local phase directly using interference or with phase reconstruction algorithms similar to those used in astronomical AO. We implemented this pupil-segmentation-based approach in a two-photon fluorescence microscope and demonstrated that diffraction-limited resolution can be recovered from nonbiological and biological samples.

We demonstrated the used of an adaptive optic system in biological imaging to improve the imaging characteristics of a wide field microscope. A crimson red fluorescent bead emitting light at 650 nm was used together with a Shack-Hartmann wavefront sensor and deformable mirror to compensate for the aberrations introduce by a Drosophila embryo. The measurement and correction at one wavelength improves the resolving power at a different wavelength, enabling the structure of the sample to be resolved (510 nm). The use of the crimson beads allow for less photobleaching to be done to the science object of the embryo, in this case our GFP model (green fluorescent beads), and allows for the science object and wavefront reference to be spectrally separated. The spectral separation allows for single points sources to be used for wavefront measurements, which is a necessary condition for the Shack-Hartmann Wavefront sensor operation.

Three-dimensional live imaging in cell biology is hindered by optical aberrations which degrade the resolution and signal-to-noise ratio as the focal plane is moved deeper into the sample. The solution to this problem is to use adaptive optics to correct the aberrations. In this paper, we discuss our work on applying adaptive optics to wide-field fluorescence microscopy. We demonstrate correction of depth-aberrations and focusing using a deformable mirror in open-loop operation. We then discuss the use of phase retrieval and phase diversity in adaptive optics.

Recently, there has been a growing interest in deep tissue imaging for the study of neurons. Unfortunately, because of the inhomogeneous refractive index of the tissue, the aberrations degrade the resolution and brightness of the final image. In this paper, we describe an adaptive optics confocal fluorescence microscope (AOCFM) which can correct aberrations based on direct wavefront measurements using a point source reference beacon and a Shack-Hartmann Wavefront Sensor (SHWS). Mouse brain tissues with different thicknesses are tested. After correction, both the signal intensity and contrast of the image are improved.