Peter Kurczynski

Supermirror hard-x-ray telescope

The practical use of a grazing x-ray telescope is demonstrated for hard-x-ray imaging as hard as 40 keV by means of a depth-graded d-spacing multilayer, a so-called supermirror. Platinum-carbon multilayers of 26 layer pairs in three blocks with a different periodic length d of 3-5 nm were designed to enhance the reflectivity in the energy range from 24 to 36 keV at a grazing angle of 0.3 deg. The multilayers were deposited on thin-replica-foil mirrors by a magnetron dc sputtering system. The reflectivity was measured to be 25%-30% in this energy range; 20 mirror shells thus deposited were assembled into the tightly nested grazing-incidence telescope. The focused hard-x-ray image was observed with a newly developed position-sensitive CdZnTe solid-state detector. The angular resolution of this telescope was found to be 2.4 arc min in the half-power diameter.

Fabrication and measurement of low-stress membrane mirrors for adaptive optics

We have fabricated low-stress membranes from single-crystal silicon for use as deformable mirrors in adaptive optics. These membranes have lower stress than membranes made from silicon nitride or other materials and therefore are capable of greater deformation than previously used membrane mirrors. Membranes were assembled into devices by flip chip bonding to electrode chips with either 256 or 1024 electrodes. We have characterized devices with static and dynamic tests and compared their performance with an analytical model. We tracked the evolution of strain in the membrane during the devices fabrication and assembly and identified sources of stress and strain in this process. We identified boron dopant concentration as a critical determinant of intrinsic stress in the membrane.

MOEMS spatial light modulator development at the Center for Adaptive Optics

The National Science Foundation Center for Adaptive Optics (CfAO) is coordinating a program for the development of spatial light modulators suitable for adaptive optics applications based on micro-optoelectromechanical systems (MOEMS) technology. This collaborative program is being conducted by researchers at several partner institutions including the Berkeley Sensor & Actuator Center, Boston Micromachines, Boston University, Lucent Technologies, the Jet Propulsion Laboratory, and Lawrence Livermore National Laboratory. The goal of this program is to produce MEMS spatial light modulators with several thousand actuators that can be used for high-resolution wavefront control applications that would benefit from low device cost, small system size, and low power requirements. The two primary applications targeted by the CfAO are astronomy and vision science. In this paper, we present an overview of the CfAO MEMS development plan along with details of the current program status.

Membrane mirrors for vision science adaptive optics

Adaptive optics provides a means to measure and correct aberrations in human vision. This technology is being used to diagnose vision problems, study the mechanism of human vision, and extend the capabilities of natures optics. The ideal wavefront corrector for vision science adaptive optics would have greater stroke, and more degrees of freedom than is currently available. Micromachined deformable mirrors may soon meet these demands. Membrane mirrors in particular offer a promising alternative to other MEMS deformable mirror designs. A new type of mirror, employing a bound charge layer on the membrane, may overcome some of the limitations of previous membrane mirrors.

Electrostatically actuated membrane mirrors for adaptive optics

We are developing membrane mirrors for use in adaptive optics, particularly in astronomy and vision science. We have micro-fabricated membrane mirrors from single crystal silicon using wet chemical etching and reactive ion etching. Membrane size, tension and operating voltage were selected to allow greater deformation of the mirror surface at low operating voltage than previous membrane mirror designs. Mirror devices consist of independently fabricated membrane and electrode array chips that are flip chip bonded together. We have fabricated electrode arrays with 256 and 1024 electrodes, and active diameters ranging from 6-10 mm (comparable to the size of the human pupil). Membrane-electrode hybrids are mounted to ceramic packages, wire bonded, and driven by off chip, D/A electronics. These devices are milestones in the development of an electret membrane mirror.

A membrane mirror with transparent electrode for adaptive optics

Membrane deformable mirror devices consist of a single large membrane that is suspended above an array of actuating electrodes. A transparent electrode is incorporated into the membrane mirror device in the optical path in an effort to provide significantly greater control of the membrane, and hence improved performance in an adaptive optics system. The devices presented here were fabricated from 1 mm thickness SOI; devices were bonded to electrode arrays with 1024 electrodes, packaged in ceramic pin grid arrays and driven by off chip D/A electronics. The transparent electrodes consist of glass that is ITO coated for electrical conductivity and visible light transmission. An electrode is inserted into a recessed cavity of each membrane chip, and is positioned 70 mm above the membrane. With 2x2 binned electrodes, the device demonstrates 10 mm deflection toward the electrode array at 40 V. Large deflection at low voltage is obtained because of the low intrinsic stress of the silicon membrane. These data also demonstrate modest deflection toward the transparent electrode, which may be improved with better alignment of the transparent electrode with the underlying membrane and electrode array in future devices.

Stability of electrostatic actuated membrane mirror devices

Membrane mirrors with transparent electrodes were fabricated for adaptive optics. These devices are capable of generating large, low-spatial-order deformations but exhibit instability for high-order deformations. A variational calculation of the electrostatic and mechanical energy of such membrane devices leads to criteria for stable operation. Simulations based upon this calculation are able to reproduce the observed behavior of fabricated devices and suggest suitable device parameters for improved performance with high-order deformations.

Low-voltage 256-electrode membrane mirror system for adaptive optics

Low stress membrane mirrors will allow improved wave front correction in vision science and astronomical adaptive optics systems. We have fabricated low stress membrane mirrors from single crystal silicon, and flip chip bonded membranes to electrode arrays. These devices operate at lower voltage and have greater stroke than existing membrane mirror devices; they have 256 control electrodes, and are driven by off chip electronics. Devices have a single electrode plane and are pre-biased to allow full wave front correction. We have demonstrated these devices in an adaptive optics system consisting of a coherent source, and a Shack-Hartmann wave front sensor. We compare the experimental performance of the devices to computer simulations and theoretical calculations.