This PDF file contains the front matter associated with SPIE Proceedings Volume 6467, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

The Lick Observatory has been a pioneer in the development of innovative technology for astronomy particularly the development of adaptive optics and laser guidestar systems. The UCO/Lick Observatory Laboratory for Adaptive Optics (LAO) is actively pursuing development of new device technologies and techniques that will enable the next generation of adaptive optics systems for astronomy. The LAO has been developing, in coordination with industry, MEMS deformable mirrors for high speed high precision wavefront control. In this paper we will present the status of the development process and the goals for the future.

In studying retinal disease on a microscopic level, in vivo imaging has allowed researchers to track disease progression in a single animal over time without sacrificing large numbers of animals for statistical studies. Historically, a drawback of in vivo retinal imaging, when compared to ex vivo imaging, is decreased image resolution due to aberrations present in the mouse eye. Adaptive optics has successfully corrected phase aberrations introduced the eye in ophthalmic imaging in humans. We are using adaptive optics to correct for aberrations introduced by the mouse eye in hopes of achieving cellular resolution retinal images of mice in vivo. In addition to using a wavefront sensor to drive the adaptive optic element, we explore the using image data to correct for wavefront aberrations introduced by the mouse eye. Image data, in the form of the confocal detection pinhole intensity are used as the feedback mechanism to control the MEMS deformable mirror in the adaptive optics system. Correction for wavefront sensing and sensor-less adaptive optics systems are presented.

We present a simple and robust way to reject out-of-focus background when performing deep two-photon excited fluorescence (TPEF) imaging in thick tissue. The technique is based on the use of a deformable mirror (DM) to introduce illumination aberrations that preferentially degrade TPEF signal while leaving TPEF background relatively unchanged. A subtraction of aberrated from unaberrated images leads to background rejection. We present a heuristic description of our technique, which we corroborate with experiment. Images of a labeled mouse olfactory bulb are compared with standard TPEF microscopy images, demonstrating significant out of focus TPEF background rejection with our technique. Finally we improve our technique by developing a faster aberration modulation mechanism that performs background subtraction line by line rather than frame by frame. In this manner, the overall image acquisition rate of our technique is the same as that of a standard TPEF microscope.

Non-linear imaging is widely used in biological imaging, primarily because of its ability to image through tissue to depth of a few hundred micrometers. Because two photons need to be absorbed to excite a fluorophore in this instrument, the probability of fluorescence emission of a detectable photon scales with the intensity squared of the beam. As a result, aberrations in the beam path that reduce the peak intensity of the focused, scanned laser spot have a significant effect on the instrument performance. Methods for reducing those aberrations should allow higher resolution and detection sensitivity, and deeper tissue imaging. In this paper, I will describe a non-linear imaging microscope that has an adaptive optics (AO) subsystem to compensate for beam path aberrations. The AO system relies on a 140 actuator deformable mirror, controlled using a stochastic gradient descent algorithm with feedback from a fluorescence sensor. The controlled instrument will be used for in vivo imaging of mouse skin, lymph nodes, and skull bone marrow at depths up to 500 &mgr;m.

For a wide range of applications in biology, medicine, and manufacturing, the small field of view associated with high resolution microscope systems poses a significant challenge in practice. This paper describes an optical microscope design, called the Adaptive Scanning Optical Microscope (ASOM), which uses a MEMS deformable mirror working with a specially designed scanning lens to achieve a greatly expanded field of view. Most adaptive optics systems (e.g. telescopes and ophthalmology instruments) are designed to achieve near ideal performance under nominal operating conditions and primarily use the adaptive optics element to compensate for a time varying disturbance to the wavefront that is external to the optical system. In contrast to this approach, the deformable mirror in the ASOM is an integral component of the optical system and the static (glass) optical elements have been specifically designed to match the shape correcting capabilities of the deformable mirror. Using a high speed steering mirror coordinated with the deformable mirror actuation voltages, the ASOM operates by scanning over the workspace and should achieve diffraction limited imaging over a region approximately two orders of magnitude larger in area than a traditional microscope design. With the rapid scanning capabilities allowed by the high speed steering mirror and by acquiring a complete image during each exposure, the ASOM offers advantages in dynamically reconfigurable and adaptable imaging with no agitation to the workspace. After describing the design and operating principle of the ASOM, we present results from a low cost ASOM prototype.

This paper explores the use of deformable membrane mirrors for primary focus control and spherical aberration correction in confocal microscopes and optical coherence tomography instruments that are miniaturized for in situ imaging. System requirements for membrane performance are explored for both high and low numerical aperture regimes. Examples of both confocal imaging and focus-tracking optical coherence tomography using vari-focus silicon nitride MEMS mirrors are presented. It is envisioned that future instruments with enhanced-stroke adaptive membrane mirrors will provide high fidelity microscopy and optical coherence tomography for diagnostic imaging of intact, living tissue.

The use of adaptive and active optics (AO) is enabling the construction and test of flexible optical systems with performances unprecedented. This flourishing of technical advances is also due to the availability of new technologies that are much lower in cost, much easier to implement and use. Among these new technologies the use of Micro-Electro- Machined (MEM) mirrors is one of the primary sources of innovation. Several groups are actively working in bringing to fruition AO systems based on MEMs technologies and at the same time several groups are working to improve the MEMs technology and tailor it more and more towards various aspects of the AO problems. This technology is especially interesting to the Navy Prototype Optical Interferometer (NPOI) upgrade. In this field several AO systems have to be constructed and operated. It is of the outmost importance that each system has a less complex and costly approach than classical AO systems.

Sandia National Laboratory has constructed several segmented MEMS deformable mirrors that are under investigation for their suitability in Adaptive Optics systems for the Naval Research Laboratory. These mirrors are constructed in a hexagonal array and have been constructed with flat surfaces, or with optical power allowing each mirror to bring its subaperture of light to a focus similar to a Shack- Hartman array. Each mirror can use the tip, tilt and piston function to move the focused spots to the desired reference location, and the measurement of the applied voltage can be used directly to power a similar flat MEMS deformable mirror. This paper reports on the suitability of this reflective wavefront sensor for closed-loop Adaptive Optics applications.

Many devices are now being used in Adaptive Optics Systems for compensating atmospheric distortions. We have developed a testbed that simulates atmospheric aberrations using a Liquid Crystal Spatial Light Modulator and the speed in which they vary may be controlled. This system allows the simulation of seeing conditions ranging from very poor to very good and these aberrations to be compensated by a second device. This second device may be a deformable mirror in conjunction with an Adaptive Optics System. Using these two devices simultaneously provides a well-defined quantitative characterization of the system and residual wavefront error using Point Spread Function and interferometric techniques.

Deployment costs of large aperture systems in space or near-space are directly related to the weight of the system. In order to minimize the weight of conventional primary mirrors and simultaneously achieve an agile system that is capable of a wider field-of-view (FOV) and true optical zoom without macroscopic moving parts, we are proposing a revolutionary alternative to conventional zoom systems where moving lenses/mirrors and gimbals are replaced with lightweight carbon fiber reinforced polymer (CFRP) variable radius-of-curvature mirrors (VRMs) and MEMS deformable mirrors (DMs). CFRP and MEMS DMs can provide a variable effective focal length, generating the flexibility in system magnification that is normally accomplished with mechanical motion. By adjusting the actuation of the CFRP VRM and MEMS DM in concert, the focal lengths of these adjustable elements, and thus the magnification of the whole system, can be changed without macroscopic moving parts on a millisecond time scale. In addition, adding optical tilt and higher order aberration correction will allow us to image off-axis, providing additional flexibility. Sandia National Laboratories, the Naval Research Laboratory, Narrascape, Inc., and Composite Mirror Applications, Inc. are at the forefront of active optics research, leading the development of active systems for foveated imaging, active optical zoom, phase diversity, and actively enhanced multi-spectral imaging. Integrating active elements into an imaging system can simultaneously reduce the size and weight of the system, while increasing capability and flexibility. In this paper, we present recent progress in developing active optical (aka nonmechanical) zoom and MEMS based foveated imaging for active imaging with a focus on the operationally responsive space application.

In order to demonstrate and to quantitatively evaluate the wavefront correction capabilities of a spatial light modulator (SLM) for optical imaging enhancement in Adaptive Optics (AO) a compact and flexible demonstration system and test bed has been developed. It basically consists of a projection system, where image objects of different complexity and spatial resolution can be implemented and imaged through Adaptive Optics onto a CCD camera. Furthermore, static and dynamic wavefront errors of different severeness can be introduced by means of fixed and rotating phase plates. With this system for the first time the optical performance of the Fraunhofer IPMS 240 × 200 micro mirror SLM for highresolution wavefront control has been characterized. For an incoherent or partially coherent imaging as employed in this case the image quality normally is assessed in terms of the Modulation Transfer Function (MTF). Therefore, a quantitative evaluation has been carried out by measuring the system MTF including the SLM for a number of spatial frequencies as well as for a variety of different complex aberrations without and with applied correction. Besides a description of the system set-up the obtained results on the imaging improvement and MTF measurement are presented.

A performance comparison is made using a number of commercially available Deformable Mirrors(DM) in fitting both ocular and atmospheric wavefronts. Least squares phase fitting simulations are performed for five mirrors using experimentally obtained mirror influence functions. The DMs used cover a range of DM technologies with varying size and cost. The phase fitting performance of these mirrors is found to be a function of influence function shape, actuator density and available mirror stroke.

As adaptive optics (AO) technology progresses, both wide-field and high-order wavefront correction systems become reachable. Deformable mirrors (DMs) in these advanced architectures must exhibit exemplary performance to give low wavefront error. Such DMs must be economically attainable, meet stroke as well as flatness requirements, and show stable and repeatable actuation. Micro-electrical mechanical systems (MEMS) deformable mirrors, undergoing testing and characterization in the Laboratory for Adaptive Optics (LAO) at the University of California at Santa Cruz, show promise on these fronts. In addition to requiring advanced deformable mirror technology, these progressive AO architectures require advanced DM control algorithms. We therefore present a formulation for accurate open-loop control of MEMS deformable mirrors. The electrostatic actuators in a discrete-actuator MEMS device are attached via posts to a thin reflective top plate. The plate itself can be well-modeled by the thin plate equation. The actuators, although nonlinear in their response to applied voltage and deformation, are independent of each other except through forces transmitted by the top plate and can be empirically modeled via a calibration procedure we will describe. In this paper we present the modeling and laboratory results. So far in the lab we have achieved open loop control to approximately 15 nm accuracy in response to arbitrary commands of approximately 500 nm amplitude. Open-loop control enables a wealth of new applications for astronomical adaptive optics instruments, particularly in multi-object integral field spectroscopy, which we will describe.

Adaptive Optics (AO) have been increasingly combined with a variety of ophthalmic instruments over the last decade to provide cellular-level, in-vivo images of the eye. The use of MEMS deformable mirrors in these instruments has recently been demonstrated to reduce system size and cost while improving performance. However, currently available MEMS mirrors lack the required range of motion for correcting large ocular aberrations, such as defocus and astigmatism. In order to address this problem, we have developed an AO system architecture that uses two deformable mirrors, in a woofer / tweeter arrangement, with a bimorph mirror as the woofer and a MEMS mirror as the tweeter. This setup provides several advantages, including extended aberration correction range, due to the large stroke of the bimorph mirror, high order aberration correction using the MEMS mirror, and additionally, the ability to 'focus' through the retina. This AO system architecture is currently being used in four instruments, including an Optical Coherence Tomography (OCT) system and a retinal flood-illuminated imaging system at the UC Davis Medical Center, a Scanning Laser Ophthalmoscope (SLO) at the Doheny Eye Institute, and an OCT system at Indiana University. The design, operation and evaluation of this type of AO system architecture will be presented.

We have designed a tip/tilt segmented mirror for the use in adaptive optics. The specific application that this device has been designed for, tracking a laser pulse through the sodium layer of our atmosphere, is well within the capabilities of this device. Through the use of finite element analysis simulations we have shown that the device has an operating voltage in the 100-150 V range, full mechanical stroke of 2.8&mgr;m, and is capable of reaching its full stroke in under 60&mgr;s. It also has shown good decoupling of the tip and tilt modes, allowing the device to track pulses that come in from any direction. Testing of the device has shown that there is a maximum of 22 percent error between the simulation and the testing results.

In some adaptive optics systems the aberration is determined not using a wave front sensor but by sequential optimization of the adaptive correction element. Efficient schemes for the control of such systems are essential if they are to be effective. One of the simplest implementations of adaptive optics requires an adaptive correction element and a single photodetector. Aberration measurement is performed by the sequential application of chosen aberrations in order to maximise the detector signal. These wave front sensorless adaptive optics systems have been demonstrated in many applications, which have included confocal microscopy, intra-cavity aberration correction for lasers, fibre coupling and optical trapping. We develop appropriate mathematical models that lead to direct maximisation algorithms with good convergence properties and that permit the measurement of N modes with only N + 1 measurements. A scheme is introduced that permits the efficient measurement of large amplitude wavefront aberrations. This scheme uses an optimization metric based upon root-mean-square spot radius and an aberration expansion using polynomials suited to the representation of lateral aberrations. The geometrical optics basis means that the scheme can be extended to arbitrarily large aberrations. We also describe a general scheme for such wave front sensorless algorithms and relate various methods to this general scheme.

For some adaptive optics (AO) systems, one deformable mirror (DM) can not meet the need of large stroke and high spatial frequency. In this paper, a double DMs way is present. In this system, a large stroke DM (LSDM) with low spatial frequency corrects low order aberrations and a high spatial frequency DM (HSFDM) with small stroke corrects high order aberrations. The decoupling algorithm of two DMs is essential for working properly. In this paper, a decoupling algorithm and experimental results for a double DM AO system are presented. The result indicates that the compensation result of double DMs AO system is almost the same as that of the conventional AO system using single DM with ideal stroke and equivalent spatial frequency.

Results of a calibrated open-loop controller for piston/tip/tilt positioning of a segmented deformable mirror are presented. The controller is based on a fit of a 3^rd-order polynomial that maps desired positions to the electrode voltages that actuate the segments. In addition to mapping positions to voltages, the controller limits positions to within the reachable space of the device. Experimental testing shows that over nearly the entire 5 &mgr;m of stroke and ±4 mrad of tip and tilt operating range, the controller positions segments to better than 30 nm rms of surface-figure error.

The main disadvantage of contemporary bimorph flexible mirrors is that they used to have rather large aperture. At the same time semipassive bimorph flexible mirror is one of the most widely used devices in various adaptive systems. We present a novel approach of multilayer bimorph (multimorph) mirrors and a numerical model to simulate them, based on a variation approach of the finite elements method in order to reduce the size (diameter) of these wavefront correctors. The multilayer bimorph mirror consists of a substrate and a number of piezoceramic layers. The electrode grid of each layer is determined separately to reproduce low order aberrations. We also present our results in reproduction of the wavefront phase dislocations (vortices) with the help of tiny bimorph mirror.

Future adaptive optics (AO) systems require deformable mirrors with very challenging parameters, up to 250 000 actuators and inter-actuator spacing around 500 &mgr;m. MOEMS-based devices are promising for the development of a complete generation of new deformable mirrors. Our micro-deformable mirror (MDM) is based on an array of electrostatic actuators with attachments to a continuous mirror on top. The originality of our approach lies in the elaboration of layers made of polymer materials. Mirror layers and active actuators have been demonstrated. Based on the design of this actuator and our polymer process, realization of a complete polymer-MDM has been done using two process flows: the first involves exclusively polymer materials while the second uses SU8 polymer for structural layers and SiO₂ and sol-gel for sacrificial layers. The latest shows a better capability in order to produce completely released structures. The electrostatic force provides a non-linear actuation, while AO systems are based on linear matrices operations. Then, we have developed a dedicated 14-bit electronics in order to "linearize" the actuation, using a calibration and a sixth-order polynomial fitting strategy. The response is nearly perfect over our 3×3 MDM prototype with a standard deviation of 3.5 nm; the influence function of the central actuator has been measured. First evaluation on the cross non-linarities has also been studied on OKO mirror and a simple look-up table is sufficient for determining the location of each actuator whatever the locations of the neighbor actuators. Electrostatic MDM are particularly well suited for open-loop AO applications.

Devices based on SOI technology are subject to bow due to residual stress induced by the buried oxide. We have designed and fabricated a compact tunable piston tip-tilt mirror device in which the shape and the arrangement of the suspension beams result in both a reduced stress in the suspension beams and an optically flat mirror. The piston tip-tilt mirror is characterized by an accurate vertical displacement of up to 18 &mgr;m @ 80 V with good repeatability, and a tip-tilt of up to 2 mrad @ 50 V.

The large-scale integration of analog operable MEMS micro-mirrors onto active CMOS address circuitry requires high quality planar reflective optical surfaces but also a stable deflection vs. voltage characteristic. However, for implementing a CMOS compatible surface micromachining process, certain obstacles like a restricted thermal budget and a limited selection of suitable materials must be overcome. In this paper, amorphous TiAl is presented as a new actuator material for monolithical MEMS integration onto CMOS circuitry at room temperature. Sputter deposited TiAl has an x-ray amorphous structure and a low stress gradient. The missing long range order and the high melting point help to virtually eliminate stress relaxation effects, i.e. TiAl hinges behave almost perfectly elastic. In a first study, 40 &mgr;m wide piston mirrors have been implemented onto substrates with fixed wired address electrode arrays. The actuators had a 300 nm TiAl core sandwiched between two layers of 25 nm Al. The devices reach a maximum deflection of about 500 nm at a dc voltage of about 23V. The drift-stability of the deflection has been tested at "worst case" conditions close to the deflection limit. During 30 min of continuous deflection near 500 nm a mechanical drift below 25nm has been observed. TiAl offers the perspective for actuators capable of a stable analog operation, which is essential to many applications, such as adaptive optics.

Adaptive optics (AO) applications in astronomy and vision science require deformable mirrors with larger stroke, higher packing density and at lower cost than currently available technology. The use of high-aspect ratio Micro-Electro- Mechanical Systems (MEMS) processing techniques to fabricate large-stroke actuators that can meet stroke, packing density and cost specifications for AO applications have been explored. Different actuator designs, materials and postprocessing procedures fabricated in two different high-aspect ratio processes have been investigated. These manufacturing processes allow high-precision multilayer fabrication, and both parallel plate and comb drive actuator deformable mirror designs have been created. Multilayer fabrication has reduced pull-in voltage requirements for large stroke comb-drive actuators. The design, modeling and simulation of these actuators are compared to experimental measurements of their pull-voltages, which characterizes their stiffness and maximum stroke.

A high-stroke micromirror array was designed, modeled, fabricated and tested. Each pixel in the 4×4 array consists of a self-aligned vertical comb drive actuator that has had a single-crystal silicon mirror successfully bonded to it. Two different bonding technologies were used, photoresist bonding and fusion bonding. The results of each of these bonding methods will be presented. Analytical models combined with CoventorWare^R simulations were used to design these elements that would move up to 10 microns in piston motion with 200V applied. Devices were fabricated according to this design and difference measurements performed with a white-light interferometer demonstrated a displacement of 0.18 microns with 200V applied. Further investigation revealed that fabrication process inaccuracy led to significantly stiffer mechanical springs in the fabricated devices. The increased stiffness of the springs was shown to account for the reduced displacement that was observed.