Deformable Mirrors For Adaptive Optics Research Articles

On the effects of spider-arms vignetting on interferometric measurements of deformable mirrors

The interferometric calibration and measurement of deformable mirrors for adaptive optics are often performed on complex optical system with spider arms. The spider shadows may divide the mirror surface into separate islands on the detector, so the interferometer fails in reconnecting them to a common phase value. The calibration measurements then suffer from such artificial differential pistons across islands, which is converted into a wrong actuator command and in general into a poor calibration. We review the effects of spider arms shadowing as experienced during the optical calibration of large format adaptive mirrors, such as the Large Binocular Telescope and Very Large Telescope ones; we describe the procedures that we tested to cope with these issues and their effectiveness; and we present a laboratory assessment of the effect of such a shadowing with a dedicated test setup. Our work is part of a preparatory activity for the optical test of the European Extremely Large Telescope adaptive mirror M4.

Eigenmode Wavefront Decoupling Algorithm for LC–DM Adaptive Optics Systems

To realize the decoupling control of the dual corrector of liquid crystal (LC)–deformable mirror (DM) adaptive optics (AO) systems and prevent the loss of correction ability induced by coupling aberrations, a wavefront decoupling method based on DM eigenmodes was proposed. The coupling relationship of two correctors was studied, and the distribution of aberrations corrected using the DM and LC was investigated. First, a DM eigenmode matrix was derived according to the DM influence function. Then, aberrations were decomposed according to the Strehl ratio, and the projection of the LC response matrix on the DM eigenmode matrix, that is, the coupling term, was derived. Before using the LC corrector, the coupling item was eliminated for the decoupling of the two correctors, and the decoupling effect was verified through simulations. Finally, a 2 m telescope LC–DM AO system was developed to validate the proposed method. The simulation and experimental results showed that the root mean square of the DM-corrected residual after 55 eigenmodes’ correction was 0.09 μm. After decoupling correction, the resolution of the 700–1700 nm wide band improved from 1.1 to 1 times the diffraction limit, which is 1.2 times better than that obtained using the traditional Zernike mode correction.

Performance evaluation of phase plate and deformable mirror for adaptive optics (AO) system

Performance evaluation of phase plate and deformable mirror for adaptive optics (AO) system

Research on elastic modes of circular deformable mirror for adaptive optics and active optics corrections.

In this paper, an elastic mode method of deformable mirror is proposed to decompose arbitrary wave-front errors of adaptive optics system. The elastic modes are derived with an analytical method of linear piezoelectricity based on a bimorph piezoelectric deformable mirror (BPDM), and the three-dimensional formulas of elastic modes are presented. Here a BPDM with an aperture of 165 mm as an example is numerically studied. Two different kinds of dynamic boundary conditions are considered, and the dependence of the elastic modes aberrations upon the orders and rotational symmetries is evaluated. Besides, a comparative study for elastic mode and Zernike polynomials is presented in the numerical analysis. The results have demonstrated that the elastic mode method can be not only used instead of Zernike polynomials, but also more effective to decompose arbitrary wave-front errors of a deformable mirror. Furthermore, finite element analysis method is used to validate the analytic method. The conclusions have shown reasonably consistent results between the two methods.

Control-structure interaction in piezoelectric deformable mirrors for adaptive optics

This paper discusses the shape control of deformable mirrors for Adaptive Optics in the dynamic range. The phenomenon of control-structure interaction appears when the mirror becomes large, lowering the natural frequencies fi, and the control bandwidth fc increases to improve the performance, so that the condition fc < fi is no longer satisfied. In this case, the control system tends to amplify the response of the flexible modes and the system may become unstable. The main parameters controlling the phenomenon are the frequency ratio fc / fi and the structural damping s. Robustness tests are developed which allow to evaluate a lower bound of the stability margin. Various passive and active strategies for damping augmentation are proposed and tested in simulation.

Zonal decoupling algorithm for dual deformable mirror adaptive optics system

A zonal decoupling algorithm used to control a dual deformable mirror (DM) is proposed. One of the two DMs is characterized with a large stroke (woofer), while the other one is characterized by a high spatial frequency (tweeter). A numerical model is used to compare the zonal decoupling algorithm with some traditional zonal decoupling algorithms. The simulation results indicate that the algorithm presented in this Letter improves the performance in suppressing the coupling error. An experimental system is built to prove the effectiveness of this algorithm. The experiments demonstrate that the phase aberrations could be effectively compensated and that the coupling error could also be suppressed.

Correlation between residual stresses and bending in functional electroceramic-based MEMS actuator

Micro-electro-mechanical systems (MEMS) technology can offer a viable alternative to realize miniaturized and less expensive actuators for deformable mirror in adaptive optics to obtain high resolution retinal imaging. During fabrication of such devices, functional multilayered thin films are deposited at elevated temperatures. These films are therefore subjected to residual stresses which may result in bending of the structure. The bending thus occurred may lead to failure at interfaces between films. A successful fabrication of device therefore relies on the engineering justification of multi-structured device design and growth parameters used in fabrication. In this paper, we present the design of a piezoelectric (ceramic) thin film based MEMS actuator for deformable mirror used in retinal imaging. A proto-type piezoelectric thin film structure of Pt/PZT/SRO/Pt/γ-Al2O3 has been epitaxially fabricated on Si (111) substrate. Advanced 3D finite element simulations were conducted to correlate the bending of fabricated structure with residual stresses. A smart alternative design was also proposed employing an extra layer of Al–Si (1%) in the diaphragm region. Simulation results predict a failsafe structure when the thickness of extra Al–Si (1%) layer is tailored to an optimal thickness. The outcome of this research can be used to overcome the challenge encountered (bending due to residual stresses) to obtain a failsafe MEMS actuator for deformable mirror.

用于自适应光学视网膜成像系统的双压电片变形反射镜

用于自适应光学视网膜成像系统的双压电片变形反射镜

Performance of 97-elements ALPAO membrane magnetic deformable mirror in Adaptive Optics - Optical Coherence Tomography system for in vivo imaging of human retina

We present an evaluation of two different configurations of the ALPAO 97-actuator membrane magnetic deformable mirror for wavefront correction, using either 7 or 9 actuators across the eye pupil. These tests included monitoring of aberration correction for a human subject. This AO-sub system is part of the UC Davis high-resolution human retinal imaging adaptive optics - optical coherence tomography (AO-OCT) instrument. AO-OCT allows the three-dimensional (3D) visualization of different retinal structures in vivo with high volumetric resolution (3x3x3?m 3 ). Full Text: PDF

Modular bimorph mirrors for adaptive optics

This paper examines the possibility of constructing deformable mirrors for adaptive optics with a large number of degrees of freedom from silicon wafers with bimorph piezoelectric actuation. The mirror may be used on its own, or as a segment of a larger mirror. The typical size of one segment is 100 to 200 mm; the production process relies on silicon wafers and thick film piezoelectric material deposition technology; it is able to lead to an actuation pitch of the order of 5 mm, and the manufacturing costs appear to grow only slowly with the number of degrees of freedom in the adaptive optics.

Materials, effects and components for tunable micro‐optics

AbstractAn overview of recent activities in the area of tunable micro‐optical components is given. These include polymer‐based deformable mirrors for adaptive optics, tunable microlenses and arrays using fluids and membranes, pneumatically actuated scanning micromirrors and tunable Bragg filters and mirrors using swelling polymers. For each device, the structure, essential fabrication technology and optical characteristics, as well as a discussion of application areas are presented. Copyright © 2007 Institute of Electrical Engineers of Japan© 2007 Institute of Electrical Engineers of Japan. Published by John Wiley &amp; Sons, Inc.

MEMS Deformable Mirrors for Adaptive Optics Actuated by Piezoelectric PZT Films

The piezoelectric MEMS deformable mirrors for adaptive optics have been developed to realize low voltage and large stroke deformable mirrors. The PZT film was deposited on a Pt-coated silicon-on-insulator (SOI) substrate and the 19 segmented electrodes were prepared on it. The circular diaphragm structure was fabricated by etching the Si substrate from the back side and the unimorph actuator array composed of a PZT film and a Si layer was accomplished. Finally a Al reflective layer was coated over the backside of the membrane as a mirror surface. The displacement profiles measurements by a laser Doppler vibrometer showed that the each actuator generated large displacement of approximately 5μm at 10V. Furthermore we could successfully reproduce the Zernike modes up to 4th order by applying the voltage calculated by control function matrix.

3304 圧電薄膜を用いた形状可変ミラーのFEM解析による設計(J26-1 マイクロメカトロニクス(1),J26 マイクロメカトロニクス)

Piezoelectric deformable mirror for adaptive optics is studied as an adaptive optics device. We have studied the piezoelectric mirror which have 19 upper electrodes. To improve the accuracy of the deformable mirror, we designed two upper electrode types, hexagonal electrodes 37ch and coaxial electrodes 35ch. To compare two electrode types, we calculated deflection of the designed mirrors by using Finite Element Method analysis simulation software, MSC. Marc. Zernike polynomials are used to evaluate the mirror surface, and the control system is based on the influence functions for generating Zernike modes. To compared with three electrodes types, 37ch, 35ch and 19ch, the residual RMS of hexagonal electrodes 37ch was the smallest, less than 0.005μm.

Aero-Optic Performance of an Aircraft Forward-Facing Optical Turret

The results of three-dimensional calculations are presented for aero-optic analysis of an aircraft forward-facing optical turret. Computational-fluid-dynamics calculations, using a compressibility corrected k-e turbulence model, defined the mean flow properties. Turbulence characteristics were obtained from a three-dimensional g law equation that yielded the variance of index-of-refraction fluctuations. The characteristic scale length of the correlation function of the index-of-refraction fluctuations was calculated. Strehl ratios and wave front distortion were computed for the mean flow and turbulence aberrations for four azimuth angles, 0, 45, 90, and 120 deg. For 90 and 120 deg azimuth, a portion of the beam passes through an open cavity with large-scale turbulence and nonuniform mean flow. For the mean flow, the Strehl ratio decreased to 0.001 at 90-deg azimuth after tip, tilt, and best focus were removed for a wavelength of 1.06 μm. The loss of Strehl as a result of turbulence was not as severe. Wind-tunnel measurements of optical path differences scale favorably to this work. In addition, instantaneous far-field intensity plots for instantaneous realizations of turbulence were constructed. A deformable mirror adaptive optics system might improve the Strehl ratio for the mean flow, but probably not for turbulence.

MOEMS, the new deformable mirrors for Adaptive Optics

Highly performing adaptive optical systems are required for next generation giant telescopes as well as next generation instrumentation for 10 m-class telescopes. Different types of AO systems are currently under study, including Multi-Conjugate AO (MCAO), high dynamic range AO, and low-order AO for distributed partial correction AO. These systems require a large variety of deformable mirrors with very challenging parameters. The development of new technologies based on micro-opto-electro-mechanical systems (MOEMS) is promising for future deformable mirrors. We are currently developing a MDM based on an array of electrostatic actuators with attachments to a continuous mirror on top. The most challenging building block for this device is the high optical quality mirror. Our first results show a very efficient planarization of the surface with our design. The integration of this mirror surface on top of an actuator array is under investigation.

적응광학계 변형거울의 구동기 배열에 따른 성능 변화 연구

적응광학계 변형거울의 구동기 배열에 따른 성능 변화 연구

Versatile seven-femtosecond pulse compressor of parametrically amplified pulses using adaptive optics: studies of the primary events in protein dynamics

High-quality, few-cycle pulses over the complete tuning range of a noncollinear parametric amplifier system and a variety of sample conditions have been readily generated using a compressor based on deformable mirror adaptive optics. These broadband pulses are compressed to 7 fs pulse duration in a compact, glassless combination of static negatively chirped mirrors and a zero-dispersion stretcher with a deformable mirror for the manipulation of the spectral phase. These ultra-short pulses are then used to investigate with very high resolution the early-time dynamics of deoxy- and carboxymyoglobin after the photoinitiated dissociation of the carbon monoxide ligand.

Segmented silicon-micromachined microelectromechanical deformable mirrors for adaptive optics

Deformable mirrors improve optical efficiency of a system by correcting the wave front aberration caused by imperfections in the system components or by turbulent atmosphere in case of telescope optics. Micromachined mirror technology has the potential to substantially reduce the cost of adaptive optics systems. First, a brief review of the work in this field is presented with the goal of informing the reader of the challenges in the micromachined adaptive optics and the implementation tradeoffs including stress-induced curvature of multilayer mirrors. Then, recent results on the silicon micromachined, hybrid integrated microelectromechanical deformable mirrors for adaptive optics developed at the University of Colorado are presented. Various microfabrication processes including surface micromachining, bulk micromachining, and flip-chip assembly are implemented to fabricate high optical fill factor and large-stroke piston-type micromirror arrays. The achieved micromirror deflection for some designs is in the range of 2 to 3.5 /spl mu/m, which results in the operating wavelength within infrared spectrum. Techniques to integrate microlenses on top of the micromirrors using self-aligned solder or transfer of ultrasmooth mirror plates on top of the micromirror actuators using flip-chip create high optical fill factor devices. Experimental results of aberration correction with such devices are presented.

Deformable mirror using magnetic membranes: application to adaptive optics in astrophysics

An alternative approach to more compact deformable mirrors for adaptive optics is developed. A thin and flexible reflective membrane is coated with a magnetic layer and locally deformed by the field created by an array of planar microcoils. This novel technology should enable higher resolution with smaller, lighter integrated mirrors. Several complementary modelling tools are used to study the electromagnetic, mechanical, magneto-mechanical and thermal behaviour of the device. A first prototype of O 30 mm mirror with a matrix of permanent magnets and an array of 25 microcoils is under construction.

Linear quadratic Gaussian control of a deformable mirror adaptive optics system with time-delayed measurements

We present a technique for controlling a ground-based deformable mirror adaptive optics telescope to compensate for optical wave-front phase distortion induced by a turbulent atmosphere. Specifically, a predictive linear quadratic Gaussian (LQG) controller is designed that generates commanded control voltages to the mirror actuators based on a set of time-delayed wave-front slope measurements from a Hartmann-type wave-front sensor.