Resonant Adaptive Mirrors

Deformable mirrors (DMs) are integrated into adaptive optical (AO) systems to compensate for wavefront aberrations. These aberrations degrade the image resolution of telescopes, microscopes, ophthalmoscopes, and optical coherent tomographs. The objective of the DM in these applications is to compensate for wavefront aberrations. Continuous and segmented DMs utilize a variety of mechanisms such as electrostatic, piezoelectric, and electromagnetic actuation. Micro-electromechanical systems (MEMS) DMs have the advantages of low cost, low power consumption, and high electrode density. As the electrode count increases, the possibility of the desired modes corresponding to the Zernike modes appearing increases. However, the complexity of the static actuation also increases. In ophthalmology, fth order Zernike modes are used to categorize the aberrations induced by the human eye. These aberrations would degrade the image resolution of the retina during laser scanning. Therefore, a dynamically continuous DMs were developed and actuated at a natural frequency corresponding to the desired Zernike mode. The actuations would drive the mirror plate to deform into the shape of the desired mode. Multiple modes corresponding to low- and high-order Zernike modes were obtained. Resonant DMs exploit the dynamic ampli cation available at natural frequency's in order to reduce voltage and power requirements. This will also reduce the requirements for spatial control of individual electrodes' voltage. However, the use of circular mirror plates to create the electromechanical modes has led to the appearance of degenerate modes (pairs of almost identical modes with closely spaced frequencies). Electrostatic elds were designed to separate those modes and help break coupling between them. The elds employ selectively, actuating some of the electrodes under the DM while grounding the rest. An AC voltage was applied to selective scheme of electrodes in order to induced mode shapes that are corresponding to the Zernike modes. This design relies on a new technique which uses pulsed laser scanning instead of continuous laser scanning. The proposed DM was designed and fabricated using a Micra-GEM fabrication process. Simulations using the nite element method (FEM) software COMSOL were used in order to determine the natural frequencies and mode shapes, and to separate degenerate modes natural frequencies by applying electrostatic elds that increase the di erence between them. Characterization of the DM was conducted using laser Doppler vibrometer to identify the mode shapes and its natural frequencies experimentally. The stroke measurements of the target DM were shown as a function of frequency and amplitude. In addition, RMS error measurements were used as a comparison between DM modes and there corresponding Zernike mode. The aim of this research was to over come the in uence function due to mechanical coupling in the continuous DMs. In uence function requires di erent voltages that apply to electrode scheme. Therefore, static actuation of the DMs rely on a complex driving circuits. Resonant DMs eliminate the e ect of the in uence function by triggering the mirror via its natural frequencies. They reduce the number of red electrode scheme by applying single voltage to the electrodes. As a result, they reduce the complexity of the driving circuits that require to control its shape. This research requires a new technique of using a pulsed laser instead of a continuous laser for the proposed DM. This may lead to manipulation of the optical laser signal using the mirror as a part of the signaling process. This should be completed by synchronizing the frequencies of both the DM and the laser to produce a high resolution image of the retina

Positioning Control System for a Large Range 2D Platform with Submicrometre Accuracy for Metrological and Manufacturing Applications

The importance of nanotechnology in the world of Science and Technology has rapidly increased over recent decades, demanding positioning systems capable of providing accurate positioning in large working ranges. In this line of research, a nanopositioning platform, the NanoPla, has been developed at the University of Zaragoza. The NanoPla has a large working range of 50 mm × 50 mm and submicrometre accuracy. The NanoPla actuators are four Halbach linear motors and it implements planar motion. In addition, a 2D plane mirror laser interferometer system works as positioning sensor. One of the targets of the NanoPla is to implement commercial devices when possible. Therefore, a commercial control hardware designed for generic three phase motors has been selected to control and drive the Halbach linear motors.This thesis develops 2D positioning control strategy for large range accurate positioning systems and implements it in the NanoPla. The developed control system coordinates the performance of the four Halbach linear motors and integrates the 2D laser system positioning feedback. In order to improve the positioning accuracy, a self calibration procedure for the characterisation of the geometrical errors of the 2D laser system is proposed. The contributors to the final NanoPla positioning errors are analysed and the final positioning uncertainty (k=2) of the 2D control system is calculated to be ±0.5 µm. The resultant uncertainty is much lower than the NanoPla required positioning accuracy, broadening its applicability scope.<br /

Applications of programmable MEMS micromirrors in laser systems

The use of optical microelectromechanical systems (MEMS) as enabling devices has been shown widely over the last decades, creating miniaturisation possibilities and added functionality for photonic systems. In the work presented in this thesis angular vertical offset comb-drive (AVC) actuated scanning micromirrors, and their use as intracavity active Q-switch elements in solid-state laser systems, are investigated. The AVC scanning micromirrors are created through a multi-user fabrication process, with theoretical and experimental investigations undertaken on the influence of the AVC initial conditions on the scanning micromirror dynamic resonant tilt movement behaviour. A novel actuator geometry is presented to experimentally investigate this influence, allowing a continuous variation of the initial AVC comb-offset angle through an integrated electrothermal actuator. The experimentally observed changes of the resonant movement with varying initial AVC offset are compared with an analytical model, simulating this varying resonant movement behaviour. In the second part of this work AVC scanning micromirrors are implemented as active intra-cavity Q-switch elements of a Nd:YAG solid-state laser system. The feasibility of achieving pulsed laser outputs with pulse durations limited by the laser cavity and not the MEMS Q-switch is shown, combined with a novel theoretical model for the Q-switch behaviour of the laser when using a bi-directional intra-cavity scanning micromirror. A detailed experimental investigation of the pulsed laser output behaviour for varying laser cavity geometries is presented, also discussing the influence of thin film coatings deposited on the mirror surfaces for further laser output power scaling. The MEMS Q-switch system is furthermore expanded using a micromirror array to create a novel Q-switched laser system with multiple individual controllable output beams using a common solid-state gain medium. Experimental results showing the simultaneous generation of two laser outputs are presented, with cavity limited pulse durations and excellent laser beam quality.The use of optical microelectromechanical systems (MEMS) as enabling devices has been shown widely over the last decades, creating miniaturisation possibilities and added functionality for photonic systems. In the work presented in this thesis angular vertical offset comb-drive (AVC) actuated scanning micromirrors, and their use as intracavity active Q-switch elements in solid-state laser systems, are investigated. The AVC scanning micromirrors are created through a multi-user fabrication process, with theoretical and experimental investigations undertaken on the influence of the AVC initial conditions on the scanning micromirror dynamic resonant tilt movement behaviour. A novel actuator geometry is presented to experimentally investigate this influence, allowing a continuous variation of the initial AVC comb-offset angle through an integrated electrothermal actuator. The experimentally observed changes of the resonant movement with varying initial AVC offset are compared with an analytical model, simulating this varying resonant movement behaviour. In the second part of this work AVC scanning micromirrors are implemented as active intra-cavity Q-switch elements of a Nd:YAG solid-state laser system. The feasibility of achieving pulsed laser outputs with pulse durations limited by the laser cavity and not the MEMS Q-switch is shown, combined with a novel theoretical model for the Q-switch behaviour of the laser when using a bi-directional intra-cavity scanning micromirror. A detailed experimental investigation of the pulsed laser output behaviour for varying laser cavity geometries is presented, also discussing the influence of thin film coatings deposited on the mirror surfaces for further laser output power scaling. The MEMS Q-switch system is furthermore expanded using a micromirror array to create a novel Q-switched laser system with multiple individual controllable output beams using a common solid-state gain medium. Experimental results showing the simultaneous generation of two laser outputs are presented, with cavity limited pulse durations and excellent laser beam quality

Development of novel high-performance six-axis magnetically levitated instruments for nanoscale applications

This dissertation presents two novel 6-axis magnetic-levitation (maglev) stages that are capable of nanoscale positioning. These stages have very simple and compact structure that is advantageous to meet requirements in the next-generation nanomanufacturing. The 6-axis motion generation is accomplished by the minimum number of actuators and sensors. The first-generation maglev stage is capable of generating translation of 300 ??m in x, y and z, and rotation of 3 mrad about the three orthogonal axes. The stage demonstrates position resolution better than 5 nm rms and position noise less than 2 nm rms. It has a light moving-part mass of 0.2126 kg. The total power consumption by all the actuators is only around a watt. Experimental results show that the stage can carry, orient, and precisely position an additional payload as heavy as 0.3 kg. The second-generation maglev stage is capable of positioning at the resolution of a few nanometers over a planar travel range of several millimeters. A novel actuation scheme was developed for the compact design of this stage that enables 6-axis force generation with just 3permanent-magnet pieces. Electromagnetic forces were calculated and experimentally verified. The complete design and construction of the second-generation maglev stage was performed. All the mechanical part and assembly fixtures were designed and fabricated at the mechanical engineering machine shop. The single moving part is modeled as a pure mass due to the negligible effect of the magnetic spring and damping. Classical as well as advanced controllers were designed and implemented for closed-loop feedback control. A nonlinear model of the force was developed and applied to cancel the nonlinearity of the actuators over the large travel range. Various experiments were conducted to test positioning, loading, and vibration-isolation capabilities. This maglev stage has a moving-part mass of 0.267 kg. Its position resolution is 4 nm over a travel range of 5 ?? 5 mm in the x-y plane. Its actuators are designed to carry and precisely position an additional payload of 2 kg. Its potential applications include semiconductor manufacturing, micro-fabrication and assembly, nanoscale profiling, and nano-indentation

MEMS-Based Endomicroscopes for High Resolution in vivo Imaging

Intravital microscopy is an emerging methodology for performing real time imaging in live animals. This technology is playing a greater role in the study of cellular and molecular biology because in vitro systems cannot adequately recapitulate the microenvironment of living tissues and systems. Conventional intravital microscopes use large, bulky objectives that require wide surgical exposure to image internal organs and result in terminal experiments. If these instruments can be reduced sufficiently in size, biological phenomena can be observed in a longitudinal fashion without animal sacrifice. The epithelium is a thin layer of tissue in hollow organs, and is the origin of many types of human diseases. In vivo assessment of biomarkers expressed in the epithelium in animal models can provide valuable information of disease development and drug efficacy. The overall goal of this work is to develop miniature imaging instruments capable of visualizing the epithelium in live animals with subcellular resolution. The dissertation is divided into four projects, where each contains an imaging system developed for small animal imaging. These systems are all designed using laser beam scanning technology with tiny mirrors developed with microelectromechanical systems (MEMS) technology. By using these miniature scanners, we are able to develop endomicroscopes small enough for hollow organs in small animals. The performance of these systems has been demonstrated by imaging either excised tissue or colon of live mice. The final version of the instrument can collect horizontal/oblique plane images in the mouse colon in real time (>10 frames/sec) with sub-micron resolution (<1 um), deep tissue penetration (~200 um) and large field of view (700 x 500 um). A novel side-viewing architecture with distal MEMS scanning was developed to create clear and stable image in the mouse colon. With the use of the instrument, it is convenient to pinpoint location of interest and create a map of the colon using image mosaicking. Multispectral fluorescence images can by collected at excitation wavelength ranging from 445 nm to 780 nm. The instruments have been used to 1) validate specific binding of a cancer targeting agent in the mouse colon and 2) study the tumor development in a mouse model with endogenous fluorescence protein expression. We use these studies to show that we have developed an enabling technology which will allow biologist to perform longitudinal imaging in animal models with subcellular resolution.PHDBiomedical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/136954/2/dxy_1.pd

Electroluminescence from Plasmonic Excitations in a Scanning Tunnelling Microscope

Die elektromagnetische Kopplung von Ladungsträgern in der Spitze eines Rastertunnelmikroskops und einer leitfähigen Probe führt zu einer plasmonischen Resonanz, die experimentell über ihren strahlenden Zerfall im optischen bis nah-infraroten Bereich zugänglich ist. Aufgrund der Verstärkung des elektrischen Feldes unmittelbar am Spitzenapex ist der optisch aktive Bereich dabei auf Abmessungen weit unterhalb der Wellenlänge des Lichts beschränkt, wobei der elektrisch stimulierte Bereich aufgrund der extremen Lokalisierung des Tunnelstroms noch kleiner ist. Dank der Möglichkeit, die Spitze auf Pikometer-Skala frei zu positionieren, eröffnet dies die einzigartige Möglichkeit, die plasmonische Kavität und ihre Resonanz sowohl hinsichtlich des Spitzen-Proben-Abstandes als auch hinsichtlich der involvierten Materialien und deren Geometrie abzustimmen, wenn die Probe lateral inhomogen ist. Diese Arbeit stellt die Gestaltung und Inbetriebnahme eines neuen Tieftemperatur-Rastertunnelmikroskops vor, welches mit einer komfortablen und effizienten Lichtsammel-Optik ausgerüstet ist. Die Integration der Spitze und eines Sammelspiegels in ein einziges, mikroskopisches Bauteil ermöglicht den einfachen in-situ Wechsel von Spitze und Probe, und umgeht viele Herausforderungen, auf die andere Experimente in der Literatur bislang gestoßen sind. Testmessungen im Zuge der Inbetriebnahme demonstrieren die Fähigkeit des neuen Instruments, Langzeit-Messungen in nie dagewesenem Ausmaß durchzuführen, und reproduzieren bekannte Effekte aus der Literatur im Detail. Überdies wird in dieser Arbeit auch zum ersten Mal Plasmon-vermittelte Lichtemission von einer wohldefinierten, hetero-epitaktisch gewachsenen Oberfläche bestehend aus zwei verschiedenen Metallen vorgestellt, nämlich Kobalt-Nanoinseln auf einer Kupfer (111) Oberfläche. Dabei zeigt die Lichtemission von unterschiedlich terminierten Teilen der Oberfläche einen signifikanten Intensitätskontrast, der auf die Energie-Abhängigkeit des zugehörigen inelastischen Tunnelübergangs zurückgeführt wird

Novel Actuation Mechanisms for MEMS Mirrors

Ph.DDOCTOR OF PHILOSOPH

Design of a high-speed-force-stroke thermomechanical micro-actuator via geometric contouring and mechanical frequency multiplication

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Includes bibliographical references (p. 187-192).The aims of this research were to understand (1) why marked performance improvements are observed when one contours the geometry of micro-thermomechanical actuators (pTMAs), (2) how to parametrically model and optimize these improvements, (3) how to use transient electrical command signals to augment these improvements, and (4) how to design arrayed pairs of actuator teams that enable the realization of these improvements within small-scale precision machines. This work has extended the performance envelope of small-scale electromechanical systems to cover the needs of emerging positioning applications that were previously impractical. The results are important to, for example, small-scale machines that are increasingly needed within biological imaging equipment, equipment for nanomanufacturing, and instruments for nano-scale research. These positioning systems must be of small geometric scale in order to achieve viable bandwidth (kHz), resolution (nanometers), cost ($10s/device) and stability (A/min) levels. Miniaturized machines require small-scale actuators, but unfortunately, state-of-the-art actuators are not capable of simultaneously satisfying the force (~10OmN), stroke (~100pLm) and bandwidth (-lkHz) requirements of the preceding applications. In the absence of a practical actuation technology, many small-scale devices were relegated to "demo" status, and they never realized the full promise that small-scale machines could deliver for the preceding applications. This work has generated two concepts - geometric contouring and mechanical frequency multiplication that make jtTMAs behave in a manner that is very different from how they have acted in the past: (1) Geometric contouring:(cont) The variation of a beam's cross-sectional area along its length to achieve more favorable thermal characteristics, i.e. temperature profile, while simultaneously reducing the elastic energy storage within the beam, and (2) Mechanical frequency multiplication: The use of pTMAs pairs that cooperate to reduce their combined cycle time below their individual cycle times, thereby increasing their operating frequency. The utility and practical implementation of these techniques were illustrated via a case study on a threeaxis optical scanner for a two-photon endomicroscope. The device consisted of three sub-systems: (i) an optical system (prism, graded index lens, and optical fiber) that was used to deliver/collect photons during imaging, (ii) a small-scale electromechanical scanner that could raster scan the focal point of the optics through a specimen and (iii) a silicon optical bench that connects the electromechanical and optical systems. The scanner was required to fit within a 7mm 0 endoscope port and scan at 1kHz throughout a 100xl00xl00 IPn3 volume. The results of this thesis were used to engineer a scanner that was capable of 3.5kHz x 100Hz x 30Hz scanning throughout a 125 x 200 x 200 jtm3 volume. Preceding jtTMA technology could only scan over 12.5% of the required volume at 10% of the required frequency. This work forms a body of knowledge - design rules, principles and best practices - that may be used to realize similar benefits in other small-scale devices.by Shih-Chi Chen.Ph.D

Design, Fabrication, and Characterization of a 2-D SOI MEMS Micromirror with Sidewall Electrodes for Confocal MACROscope Imaging

Micro-Electro-Mechanical Systems (MEMS) micromirrors have been developed for more than two decades along with the development of MEMS technology. They have been used into many application fields: optical switches, digital light projector (DLP), adoptive optics (AO), high definition (HD) display, barcode reader, endoscopic optical coherence tomography (OCT) and confocal microscope, and so on. Especially, MEMS mirrors applied into endoscopic OCT and confocal microscope are the intensive research field. Various actuation mechanisms, such as electrostatic, electromagnetic, electro bimorph thermal, electrowetting, piezoelectric (PZT) and hybrid actuators, are adopted by different types of micromirrors. Among these actuators, the electrostatic is easily understood and simple to realize, therefore, it is broadly adopted by a large number of micromirrors. This thesis reports the design, fabrication, and characterization of a 2-D Silicon-on-insulation (SOI) MEMS micromirror with sidewall (SW) electrodes for endoscopic OCT or confocal microscope imaging. The biaxial MEMS mirror with SW electrodes is actuated by electrostatic actuators. The dimension of mirror plate is 1000micron×1000micron, with a thickness of a 35micron. The analytical modeling of SW electrodes, fabrication process, and performance characteristics are described. In comparison to traditional electrostatic actuators, parallel-plate and comb-drive, SW electrodes combined with bottom electrodes achieve a large tilt angle under a low drive voltage that the comb-drive does and possess fairly simple fabrication process same as that of the parallel-plate. A new fabrication process based on SOI wafer, hybrid bulk/surface micromachined technology, and a high-aspect-ratio shadow mask is presented. Moreover, the fabrication process is successfully extended to fabricate 2×2 and 4×4 micromirror arrays. Finally, a biaxial MEMS mirror with SW electrodes was used into Confocal MACROscope for imaging. Studied optical requirements in terms of two optical configurations and frequency optimization of the micromirror, the biaxial MEMS mirror replaces the galvo-scanner and improves the MACROscope. Meanwhile, a new Micromirror-based Laser Scanning Microscope system is presented and allows 2D images to be acquired and displayed

Robot-assisted Optical Ultrasound Scanning

Optical ultrasound, where ultrasound is both generated and received using light, can be integrated in very small diameter instruments making it ideally suited to minimally invasive interventions. One-dimensional information can be obtained using a single pair of optical fibres comprising of a source and detector but this can be difficult to interpret clinically. In this paper, we present a robotic-assisted scanning solution where a concentric tube robot manipulates an optical ultrasound probe along a consistent trajectory. A torque coil is utilised as a buffer between the curved nitinol tube and the probe to prevent torsion on the probe and maintain the axial orientation of the probe while the tube is rotating. The design and control of the scanning mechanism are presented along with the integration of the mechanism with a fibre-based imaging probe. Trajectory repeatability is assessed using electromagnetic tracking and a technique to calibrate the transformation between imaging and robot coordinates using a known model is presented. Finally, we show example images of 3D printed phantoms generated by collecting multiple OpUS A-scans within the same 3D scene to illustrate how robot-assisted scanning can expand the field of view