This PDF file contains the front matter associated with SPIE Proceedings Volume 8253, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

NASA and the astronomy community hope to soon launch a new space-based telescope to detect and characterize extrasolar planets. Detecting extrasolar planets with angular separations and contrast levels similar to Earth requires not only a large space-based observatory but also advanced starlight suppression techniques. One promising approach is coronagraphy via shaped pupils. Shaped pupil coronagraphs are binary pupil functions that modify the point spread function of a telescope to produce regions of high contrast. Unfortunately, the contrast performance of coronagraphs is highly sensitive to optical errors, thus necessitating wavefront control to retrieve the necessary contrast levels. Using two MEMS deformable mirrors in series with the coronagraph allows us to control both the phase and amplitude aberrations over a finite wavelength range. Given an estimate of the wavefront we have developed an optimal controller that minimizes actuator strokes on the deformable mirrors subject to a constraint that it achieve a targeted contrast level in a defined region of the image. To provide an estimate for the controller that is accurate enough to converge to a solution that achieves the required ten orders of magnitude, the electric field must be estimated using the science camera to avoid any non-common path errors. The estimate is found by either using a batch process or Kalman filter technique which uses multiple image pairs with conjugated deformable mirror settings to estimate the field prior to evaluating the control shape. This paper outlines the algorithms used and presents our laboratory results.

Micro-electro-mechanical systems (MEMS) technology can provide for deformable mirrors (DMs) with excellent performance within a favorable economy of scale. Large MEMS-based astronomical adaptive optics (AO) systems such as the Gemini Planet Imager are coming on-line soon. As MEMS DM end-users, we discuss our decade of practice with the micromirrors, from inspecting and characterizing devices to evaluating their performance in the lab. We also show MEMS wavefront correction on-sky with the "Villages" AO system on a 1-m telescope, including open-loop control and visible-light imaging. Our work demonstrates the maturity of MEMS technology for astronomical adaptive optics.

In this paper is described a "push-pull" deformable mirror which has the advantage that the mirror membrane can either be attracted from the back or from the front giving several advantages such as: doubled dynamic, better accuracy in mode reproduction, and bidirectional deformation. The key idea when developing this push-pull deformable mirror was to have good compromise between performances and practical applicability for series production. An analysis of the constraints/practical limitations is described using simulations and laboratory tests. Following the results, we forsee the benefits of inserting the push-pull DM (Saturn, Adaptica Srl) in practical applications such as ophthalmology and microscopy.

MEMS deformable mirrors with thousands of actuators are under development for space-based operation, which require fault tolerant actuators that will not fail due to electrical overstress. We report on advances made in the development of MEMS deformable mirror actuators with enhanced reliability for space-based, high-contrast imaging instrumentation that eliminate irreversible actuator damage resulting from snap-through.

The areas of biological microscopy, ophthalmic research, and atmospheric turbulence correction require high-order DMs to obtain diffraction-limited images. Iris AO has been developing high-order MEMS DMs to address these requirements. Recent development has resulted in fully functional 489-actuator DMs capable of 9.5 µm stroke. For laser applications, the DMs were modified to make them compatible with high-reflectance dielectric coatings. Experimental results for the 489-actuator DMs with dielectric coatings shows they can be made with superb optical quality λ/93.3 rms (11.4 nm rms) and λ/75.9 rms (20.3 nm rms) for 1064 nm and 1540 nm coatings. Laser testing has demonstrated 300 W/cm2 power handling with off-the-shelf packaging. Power handling of 2800 W/cm2 is projected when incorporating packaging optimized for heat transfer.

After laboratory studies have demonstrated that the DM-based adaptive optics ophthalmic instruments are promising for future clinical applications, the next step would be to further enhance the functionality of ocular adaptive optics for research and commercialize it for clinical applications. The first essential requirement is the stroke which should cover most wavefront errors of the eyes in clinical population, for which, we presented here design, modeling, and experimental performance of PMN-PT unimorph actuators suitable for generating large stroke up to 50μm per 1-mm pixel in order to cover wavefront correction for older adults and patients with diseased eyes. Clinical acceptance will also requires DMs to be low cost, have a small form factor, running low power, have satisfactory speed, and be an easy add-on for system integration, thus we further presented an effort of developing a high voltage amplifier (HVA) based application specific integrated circuits (ASIC) for driving the mirror actuators with significantly reduced power and system form factors.

We have developed a new type of unimorph deformable mirror for real-time intra-cavity phase control of high power cw-lasers. The approach is innovative in its combination of super-polished and pre-coated highly reflective substrates, the miniaturization of the unimorph principle, and the integration of a monolithic tip/tilt functionality. Despite the small optical aperture of only 9 mm diameter, the mirror is able to produce a stroke of several microns for low order Zernike modes, paired with a residual static root-mean-square aberration of less than 0.04 μm. In this paper, the characteristics of the mirror such as the influence functions, the dynamic behavior, and the power handling capability are reported. The mirror was subjected to a maximum of 490 W of laser-light at a wavelength of 1030 nm. Due to the high reflectivity of over 99.998 % the mirror is able to withstand intensities up to 1.5 MW/cm².

We report on an effort of building a new form of deformable mirror (DM) driven by an array of giant piezo microactuators and being integrated with an ASIC driver electronics. The actuator layer is obtained by bonding a thin Si wafer with a thin PMN-PT crystal substrate, and is in attachment with a bulk-micromachined mirror hierarchy comprising of a supporting Si layer as the spacer, a Si post layer as the motion sampler, and atop of which a Si micromembrane layer as the deformable mirror. The ASIC employs a charge controlled approach to actuate the large capacitance (~nF) in associating with the high-energy-density actuators, capable of charging/discharging an array from quasi-static to 20 kHz framing rate, and with ultra-low-power dissipation that approximates the theoretical minimum of a driver electronics. The DM to ASIC integration is currently accomplished at chip level. An integrated DM prototype has 32x32 actuator elements at 600um pitch, weighing ~50 grams, as compact as ~1 cubic inch, and uses 25 wires to access the 1024 actuators. Fundamental characterizations of a few ASIC drivers are also presented.

Thin-shelled composite mirrors have been recently proposed as both deformable mirrors for aberration correction and as variable radius of curvature mirrors for phase diversity, auto focus, and adaptive optical zoom. The requirements of actuation of a composite mirror far surpass those for MEMS deformable mirrors. This paper will discuss the development of a finite element model for a 0.2 meter carbon fiber reinforced polymer mirror for use as a variable radius of curvature mirror in conjunction with a MEMS deformable mirror for aberration correction.

This paper reports on the thermo-mechanical modeling and characterization of a screen printed deformable mirror. The unimorph mirror offers a ceramic LTCC substrate with screen printed PZT layers on its rear surface and a machined copper layer on its front surface. We present the thermo-mechanical model of the deformable mirror based on Ansys multiphysics. The developed mirror design is practically characterized. The homogeneous loading of the optimized design results in a membrane deformation with a rate of -0.2 μm/K, while a laser loading causes a change with a rate of 1.3 μm/W. The proposed mirror design is also suitable to pre-compensate laser generated mirror deformations by homogeneous thermal loading (heating). We experimentally show that a 35 K pre-heating of the mirror assembly could compensate an absorbed laser power of 1.25 W.

We have implemented a coherence-gated wavefront sensor on a two-photon excitation microscope. We used the backscattered near-infrared light from the sample to interfere with an optically flat reference beam. By applying a known waverfront tilt in the reference beam, a fringe pattern emerged on the camera. The deformmation of the wavefront due to the turbid media under study warps the fring pattern, similar to frequency modulation. Through Fourier transform analysis of the modulated fringe pattern we were able to determine the wave fornt aberrations induced by synthetic and biological samples. By defocussing the microscope objective and measuring the wavefront deformation we established that the errors are reproduceible to within λ/227 for the defocus mode.

Modal sensorless adaptive optics relies on the use of an image quality metric to estimate the amplitude of aberrations, and of a well-suited set of aberration modes to describe the aberration. This set is chosen so that aberration of one mode does not influence correction in another mode. In this paper, we show how these modes can be derived experimentally, and investigate the influence of imperfect crosstalk removal on the accuracy of correction. We show that the resulting error can be mitigated using appropriate algorithms that can incorporate knowledge of the influence of the modes on the metric and, if available, partial knowledge of the aberrations. Finally, we derive from these results the minimum time required for correction in various situations.

Phase Diversity is a powerful technique for estimating wavefront aberrations from images of extended scenes. Phase Diversity was developed for two-dimensional imaging, typically using defocus as the phase diverse aberration. Here we discuss different approaches for extending phase diversity to three-dimensional imaging for biological applications. We show the results of using phase diversity to determine wavefront aberrations on simulated images.

In this paper we present an alignment methodology for a non-linear laser scanning fluorescence microscopic imaging system integrated with a MEMS deformable mirror that is used to compensate microscope aberrations and improve sample image quality. The procedure uses an accurate open-loop control mechanism of the MEMS DM, a high resolution CMOS camera and a compact Shack-Hartmann wavefront sensor. The success of the indirect AO control method used by the microscope to compensate aberrations requires careful alignment of the optical system, specifically the DM conjugate planes in the scanning laser optical path. Considerations of this procedure are presented here, in addition to an assessment of the final accuracy of the alignment task is presented, by verifying the pupil conjugation and wavefront response. This method can also serve as a regular check-up of the system's performance and trouble-shoot for system misalignment.

Adaptive optics have been used to compensate the detrimental effects of aberrations in a range of high resolution microscopes. Aberration measurement has been implemented in various way, using direct wave front sensing or indirect optimisation methods. We investigate how backscattered laser illumination can be used as the source for direct wave front sensing using a pinhole filtered Shack Hartmann wave front sensor. It is found that the sensor produces linear response to input aberrations for a given specimen. The gradient of this response is dependent upon experimental configuration and specimen structure. The double pass nature of the microscope system leads to lower sensitivity to odd-symmetry aberration modes.

We report on the development of a widefield microscope that achieves adaptive optics correction through the use of a wavefront sensor observing an artificial laser guide star induced within the sample. By generating this guide star at arbitrary positions and depths within the sample we allow the delivery of high-resolution images. This approach delivers much faster AO correction than image optimization techniques, and allows the use of AO with fluorescent imaging modalities without generating excessive photo-toxic damage in the sample, or inducing significant photo-bleaching in the flurophore molecules.

A reflective microelectromechanical mirror array was used to control the intensity distribution of a coherent beam that was propagated through a strongly scattering medium. The controller modulated phase spatially in a plane upstream of the scattering medium and monitored intensity spatially in a plane downstream of the medium. Optimization techniques were used to maximize the intensity at a single point in the downstream plane. Intensity enhancement by factors of several hundred were achieved within a few thousand iterations using a MEMS segmented deformable mirror (e.g. a spatial light modulator) with 1020 independent segments. Experimental results are reported for alternate optimization approaches and for optimization through dynamically translating scattering media.

Optical aberrations due to the inhomogeneous refractive index of tissue degrade the resolution and brightness of images in deep tissue imaging. We introduce a direct wavefront sensing method using cellular structures labeled with fluorescent proteins in tissues as guide-stars. As a non-invasive and high-speed method, it generalizes the direct wavefront sensing method for adaptive optics microscopy. An adaptive optics confocal microscope using this method is demonstrated for imaging of mouse brain tissue. The confocal images with and without correction are collected. The results show increased image contrast and 3X improvement in the signal intensity for fixed mouse tissues at a depth of 70 μm. The images of the dendrite and spines are much clearer after correction with improved contrast. The Strehl ratio is improved from 0.29 to 0.96, a significant 3.3X improvement.

Dynamic maskless holographic lithography (DMHL) is a new micro-manufacturing technique that has no moving parts. The laser light used for patterning is directed in all three dimensions with a hologram displayed on a liquid-crystal spatial light modulator (SLM). Optical aberrations, like spherical aberration due to refractive index mismatch between the photoresist and the immersion oil of the high-NA objective or astigmatism due to the deformations in the surface of the SLM, can degrade the performance of the system. Degraded performance includes a decrease in potential patterning volume and pattern fidelity and an increase in patterning time. This paper presents a way to correct for these aberrations using Zernike polynomials. The optimal Zernike coefficients are found by maximizing a sharpness metric. The effect of aberration correction on the DMHL process is quantified by measuring the patterning volume. DMHL manufactured features made with this aberration correction method show a marked improvement over features made without correction. It is even possible to correct for misaligned optics with this method.

We describe an accommodating lens patterned after the crystalline lens of the eye. Our biomimetic MEMS design calls to mind the zonules of zinn which pull radially to stretch the crystalline lens of the eye to modify the optical path. We present initial characterization of the prototype macro-scale device constructed through traditional machining techniques and using a PDMS polymer lens. Testing of the macro-scale lens indicated a 22% change in focal length through the range of radial stretching, with degradation of the spherical lens shape but no hysteresis after low-cycle testing. We also demonstrate a MEMS implementation of the lens actuator constructed using the Sandia SUMMiT-V ™ surface micromachining process. The optical path of this system is approximately 300 microns in diameter, providing a platform to potential applications improving mobile camera optics and medical imaging.