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AO Group Annual Report

Description: The Adaptive Optics (AO) Group in I Division develops and tests a broad range of advanced wavefront control technologies. Current applications focus on: Remote sensing, High power lasers, Astronomy, and Human vision. In the area of remote sensing, the AO Group leads a collaborative effort with LLNL's Nonproliferation, Arms Control & International Security (NAI) Directorate on Enhanced Surveillance Imaging. The ability to detect and identify individual people or vehicles from long-range is an important requirement for proliferation detection and homeland security. High-resolution imaging along horizontal paths through the atmosphere is limited by turbulence, which blurs and distorts the image. For ranges over {approx}one km, visible image resolution can be reduced by over an order of magnitude. We have developed an approach based on speckle imaging that can correct the turbulence-induced blurring and provide high resolution imagery. The system records a series of short exposure images which freeze the atmospheric effects. We can then estimate the image magnitude and phase using a bispectral estimation algorithm which cancels the atmospheric effects while maintaining object information at the diffraction limit of the imaging system.
Date: October 4, 2005
Creator: Olivier, S
Partner: UNT Libraries Government Documents Department

Adaptive Optics Applications in Vision Science

Description: Adaptive optics can be used to correct the aberrations in the human eye caused by imperfections in the cornea and the lens and thereby, improve image quality both looking into and out of the eye. Under the auspices of the NSF Center for Adaptive Optics and the DOE Biomedical Engineering Program, Lawrence Livermore National Laboratory has joined together with leading vision science researchers around the country to develop and test new ophthalmic imaging systems using novel wavefront corrector technologies. Results of preliminary comparative evaluations of these technologies in initial system tests show promise for future clinical utility.
Date: March 17, 2003
Creator: Olivier, S S
Partner: UNT Libraries Government Documents Department

Advanced Adaptive Optics Technology Development

Description: The NSF Center for Adaptive Optics (CfAO) is supporting research on advanced adaptive optics technologies. CfAO research activities include development and characterization of micro-electro-mechanical systems (MEMS) deformable mirror (DM) technology, as well as development and characterization of high-resolution adaptive optics systems using liquid crystal (LC) spatial light modulator (SLM) technology. This paper presents an overview of the CfAO advanced adaptive optics technology development activities including current status and future plans.
Date: September 18, 2001
Creator: Olivier, S
Partner: UNT Libraries Government Documents Department

A Security Solution for IEEE 802.11's Ad-hoc Mode:Password-Authentication and Group Diffie-Hellman Key Exchange

Description: The IEEE 802 standards ease the deployment of networkinginfrastructures and enable employers to accesscorporate networks whiletraveling. These standards provide two modes of communication calledinfrastructure and ad-hoc modes. A security solution for the IEEE802.11's infrastructure mode took several years to reach maturity andfirmware are still been upgraded, yet a solution for the ad-hoc modeneeds to be specified. The present paper is a first attempt in thisdirection. It leverages the latest developments in the area ofpassword-based authentication and (group) Diffie-Hellman key exchange todevelop a provably-secure key-exchange protocol for IEEE 802.11's ad-hocmode. The protocol allows users to securely join and leave the wirelessgroup at time, accommodates either a single-shared password orpairwise-shared passwords among the group members, or at least with acentral server; achieves security against dictionary attacks in theideal-hash model (i.e. random-oracles). This is, to the best of ourknowledge, the first such protocol to appear in the cryptographicliterature.
Date: October 1, 2005
Creator: Emmanuel, Bresson; Olivier, Chevassut & David, Pointcheval
Partner: UNT Libraries Government Documents Department

Performance predictions for the Keck telescope adaptive optics system

Description: The second Keck ten meter telescope (Keck-11) is slated to have an infrared-optimized adaptive optics system in the 1997--1998 time frame. This system will provide diffraction-limited images in the 1--3 micron region and the ability to use a diffraction-limited spectroscopy slit. The AO system is currently in the preliminary design phase and considerable analysis has been performed in order to predict its performance under various seeing conditions. In particular we have investigated the point-spread function, energy through a spectroscopy slit, crowded field contrast, object limiting magnitude, field of view, and sky coverage with natural and laser guide stars.
Date: August 7, 1995
Creator: Gavel, D.T. & Olivier, S.S.
Partner: UNT Libraries Government Documents Department

Design issues in the semantics and scheduling of asynchronous tasks.

Description: The asynchronous task model serves as a useful vehicle for shared memory parallel programming, particularly on multicore and manycore processors. As adoption of model among programmers has increased, support has emerged for the integration of task parallel language constructs into mainstream programming languages, e.g., C and C++. This paper examines some of the design decisions in Cilk and OpenMP concerning semantics and scheduling of asynchronous tasks with the aim of informing the efforts of committees considering language integration, as well as developers of new task parallel languages and libraries.
Date: July 1, 2013
Creator: Olivier, Stephen L.
Partner: UNT Libraries Government Documents Department

Provably-Secure Authenticated Group Diffie-Hellman KeyExchange

Description: Authenticated key exchange protocols allow two participantsA and B, communicating over a public network and each holding anauthentication means, to exchange a shared secret value. Methods designedto deal with this cryptographic problem ensure A (resp. B) that no otherparticipants aside from B (resp. A) can learn any information about theagreed value, and often also ensure A and B that their respective partnerhas actually computed this value. A natural extension to thiscryptographic method is to consider a pool of participants exchanging ashared secret value and to provide a formal treatment for it. Startingfrom the famous 2-party Diffie-Hellman (DH) key exchange protocol, andfrom its authenticated variants, security experts have extended it to themulti-party setting for over a decade and completed a formal analysis inthe framework of modern cryptography in the past few years. The presentpaper synthesizes this body of work on the provably-secure authenticatedgroup DH key exchange.
Date: January 1, 2007
Creator: Bresson, Emmanuel; Chevassut, Olivier & Pointcheval, David
Partner: UNT Libraries Government Documents Department

Large-Stroke Self-Aligned Vertical Comb Drive Actuators for Adaptive Optics Applications

Description: A high-stroke micro-actuator array was designed, modeled, fabricated and tested. Each pixel in the 4x4 array consists of a self-aligned vertical comb drive actuator. This micro-actuator array was designed to become the foundation of a micro-mirror array that will be used as a deformable mirror for adaptive optics applications. Analytical models combined with CoventorWare{reg_sign} simulations were used to design actuators that would move up to 10{micro}m in piston motion with 100V applied. Devices were fabricated according to this design and testing of these devices demonstrated an actuator displacement of 1.4{micro}m 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 of the actuators relative to the design.
Date: October 27, 2005
Creator: Carr, E J; Olivier, S S & Solgaard, O
Partner: UNT Libraries Government Documents Department

Laser guide star adaptive optics: Present and future

Description: Feasibility demonstrations using one to two meter telescopes have confirmed the utility of laser beacons as wavefront references for adaptive optics systems. Laser beacon architectures suitable for the new generation of eight and ten meter telescopes are presently under study. This paper reviews the concept of laser guide star adaptive optics and the progress that has been made by groups around the world implementing such systems. A description of the laser guide star program at LLNL and some experimental results is also presented.
Date: March 1, 1993
Creator: Olivier, S. S. & Max, C. E.
Partner: UNT Libraries Government Documents Department

Simulation and analysis of laser guide star adaptive optics systems for the eight to ten meter class telescopes

Description: This paper discusses the design and analysis of laser-guided adaptive optic systems for the large, 8--10 meter class telescopes. We describe a technique for calculating the expected modulation transfer function and the point spread function for a closed loop adaptive optics system, parameterized by the degree of correction and the seeing conditions. The results agree closely with simulations and experimental data, and validate well known scaling law models even at low order correction. Scaling law.model analysis of a proposed adaptive optics system at the Keck telescope leads to the conclusion that a single laser guide star beacon will be adequate for diffraction limited imaging at wavelengths between 1 and 3 am with reasonable coverage of the sky. Cone anisoplanatism will dominate wavefront correction error at the visible wavelengths unless multiple laser guide stars are used.
Date: March 1, 1994
Creator: Gavel, D. T. & Olivier, S. S.
Partner: UNT Libraries Government Documents Department

Coherent Communications, Imaging and Targeting

Description: Laboratory and field demonstration results obtained as part of the DARPA-sponsored Coherent Communications, Imaging and Targeting (CCIT) program are reviewed. The CCIT concept uses a Phase Conjugation Engine based on a quadrature receiver array, a hologram processor and a spatial light modulator (SLM) for high-speed, digital beam control. Progress on the enabling MEMS SLM, being developed by a consortium consisting of LLNL, academic institutions and small businesses, is presented.
Date: October 3, 2003
Creator: Stappaerts, E; Baker, K; Gavel, D; Wilks, S; Olivier, S; Brase, J et al.
Partner: UNT Libraries Government Documents Department

Performance of keck adaptive optics with sodium laser guide star

Description: The Keck telescope adaptive optics system is designed to optimize performance in he 1 to 3 micron region of observation wavelengths (J, H, and K astronomical bands). The system uses a 249 degree of freedom deformable mirror, so that the interactuator spacing is 56 cm as mapped onto the 10 meter aperture. 56 cm is roughly equal to r0 at 1.4 microns, which implies the wavefront fitting error is 0.52 ({lambda}/2{pi})({ital d}/{ital r}{sub 0}){sup 5/6} = 118 nm rms. This is sufficient to produce a system Strehl of 0.74 at 1.4 microns if all other sources of error are negligible, which would be the case with a bright natural guidestar and very high control bandwidth. Other errors associated with the adaptive optics will however contribute to Strehl degradation, namely, servo bandwidth error due to inability to reject all temporal frequencies of the aberrated wavefront, wavefront measurement error due to finite signal-to-noise ratio in the wavefront sensor, and, in the case of a laser guidestar, the so-called cone effect where rays from the guidestar beacon fail to sample some of the upper atmosphere turbulence. Cone effect is mitigated considerably by the use of the very high altitude sodium laser guidestar (90 km altitude), as opposed to Rayleigh beacons at 20 km. However, considering the Keck telescope`s large aperture, this is still the dominating wavefront error contributor in the current adaptive optics system design.
Date: March 8, 1996
Creator: Gavel, D.T.; Olivier, S. & Brase, J.
Partner: UNT Libraries Government Documents Department

Dynamic Group Diffie-Hellman Key Exchange under standard assumptions

Description: Authenticated Diffie-Hellman key exchange allows two principals communicating over a public network, and each holding public-private keys, to agree on a shared secret value. In this paper we study the natural extension of this cryptographic problem to a group of principals. We begin from existing formal security models and refine them to incorporate major missing details (e.g., strong-corruption and concurrent sessions). Within this model we define the execution of a protocol for authenticated dynamic group Diffie-Hellman and show that it is provably secure under the decisional Diffie-Hellman assumption. Our security result holds in the standard model and thus provides better security guarantees than previously published results in the random oracle model.
Date: February 14, 2002
Creator: Bresson, Emmanuel; Chevassut, Olivier & Pointcheval, David
Partner: UNT Libraries Government Documents Department

Initial results from the Lick Observatory Laser Guide Star Adaptive Optics System

Description: A prototype adaptive optics system has been installed and tested on the 3 m Shane telescope at Lick Observatory. The adaptive optics system performance, using bright natural guide stars, is consistent with expectations based on theory. A sodium-layer laser guide star system has also been installed and tested on the Shane telescope. Operating at 15 W, the laser system produces a 9th magnitude guide star with seeing-limited size at 589 nm. Using the laser guide star, the adaptive optics system has reduced the wavefront phase variance on scales above 50 cm by a factor of 4. These results represent the first continuous wavefront phase correction using a sodium-layer laser guide star. Assuming tip-tilt is removed using a natural guide star, the measured control loop performance should produce images with a Strehl ratio of 0.4 at 2.2 {mu}m in 1 arc second seeing. Additional calibration procedures must be implemented in order to achieve these results with the prototype Lick adaptive optics system.
Date: November 8, 1995
Creator: Olivier, S.S.; An, J. & Avicola, K.
Partner: UNT Libraries Government Documents Department

Conceptual design for a user-friendly adaptive optics system at Lick Observatory

Description: In this paper, we present a conceptual design for a general-purpose adaptive optics system, usable with all Cassegrain facility instruments on the 3 meter Shane telescope at the University of California`s Lick Observatory located on Mt. Hamilton near San Jose, California. The overall design goal for this system is to take the sodium-layer laser guide star adaptive optics technology out of the demonstration stage and to build a user-friendly astronomical tool. The emphasis will be on ease of calibration, improved stability and operational simplicity in order to allow the system to be run routinely by observatory staff. A prototype adaptive optics system and a 20 watt sodium-layer laser guide star system have already been built at Lawrence Livermore National Laboratory for use at Lick Observatory. The design presented in this paper is for a next- generation adaptive optics system that extends the capabilities of the prototype system into the visible with more degrees of freedom. When coupled with a laser guide star system that is upgraded to a power matching the new adaptive optics system, the combined system will produce diffraction-limited images for near-IR cameras. Atmospheric correction at wavelengths of 0.6-1 mm will significantly increase the throughput of the most heavily used facility instrument at Lick, the Kast Spectrograph, and will allow it to operate with smaller slit widths and deeper limiting magnitudes. 8 refs., 2 figs.
Date: March 8, 1996
Creator: Bissinger, H.D.; Olivier, S. & Max, C.
Partner: UNT Libraries Government Documents Department

Provably authenticated group Diffie-Hellman key exchange - The dynamic case (Extended abstract)

Description: Dynamic group Diffie-Hellman protocols for Authenticated Key Exchange(AKE) are designed to work in scenario in which the group membership is not known in advance but where parties may join and may also leave the multicast group at any given time. While several schemes have been proposed to deal with this scenario no formal treatment for this cryptographic problem has ever been suggested. In this paper, we define a security model for this problem and use it to precisely define Authenticated Key Exchange (AKE) with ''implicit'' authentication as the fundamental goal, and the entity-authentication goal as well. We then define in this model the execution of a protocol modified from a dynamic group Diffie-Hellman scheme offered in the literature and prove its security.
Date: September 20, 2001
Creator: Bresson, Emmanuel; Chevassut, Olivier & Pointcheval, David
Partner: UNT Libraries Government Documents Department

Evaluation of chromium speciation and transport characteristics in the Hanford Site 100D and 100H areas

Description: Field and laboratory investigations have been conducted to define the fate and transport characteristics of chromium contamination present in the 100D/H Areas of the Hanford Site. This information is relevant to assessing the impact of the release of hexavalent chromium to the Columbia River. Included in this study was the determination of the concentration and aqueous speciation of chromium in the unconfined acquifer and an assessment of potential changes in speciation as groundwater passes through the river/acquifer transition zone and mixes with the Columbia River. The results of this study indicate that chromium present within the Hanford acquifer is predominantly in the oxidized hexavalent state. Chromium is apparently stable in the oxidized form owing to its lack of organic matter within the acquifer. A portion of the chromium is removed as groundwater passes through the transition zone due to reduction and precipitation associated with sediment/water interaction processes. Chemical data collected from seep water samples, however, suggests, that most of the hexavalent chromium ultimately discharges into the Columbia River. Dilution of hexavalent chromium subsequently occurs during the mixing of groundwater and river water, with relatively little change taking place in speciation.
Date: August 1, 1995
Creator: Thornton, E.C.; Amonette, J.E. & Olivier, J.
Partner: UNT Libraries Government Documents Department

New Security Results on Encrypted Key Exchange

Description: Schemes for encrypted key exchange are designed to provide two entities communicating over a public network, and sharing a (short) password only, with a session key to be used to achieve data integrity and/or message confidentiality. An example of a very efficient and ''elegant'' scheme for encrypted key exchange considered for standardization by the IEEE P1363 Standard working group is AuthA. This scheme was conjectured secure when the symmetric-encryption primitive is instantiated via either a cipher that closely behaves like an ''ideal cipher,'' or a mask generation function that is the product of the message with a hash of the password. While the security of this scheme in the former case has been recently proven, the latter case was still an open problem. For the first time we prove in this paper that this scheme is secure under the assumptions that the hash function closely behaves like a random oracle and that the computational Diffie-Hellman problem is difficult. Furthermore, since Denial-of-Service (DoS) attacks have become a common threat we enhance AuthA with a mechanism to protect against them.
Date: December 15, 2003
Creator: Bresson, Emmanuel; Chevassut, Olivier & Pointcheval, David
Partner: UNT Libraries Government Documents Department

The group Diffie-Hellman problems

Description: In this paper they study generalizations of the Diffie-Hellman problems recently used to construct cryptographic schemes for practical purposes. The Group Computational and the Group Decisional Diffie-Hellman assumptions not only enable one to construct efficient pseudo-random functions but also to naturally extend the Diffie-Hellman protocol to allow more than two parties to agree on a secret key. In this paper they provide results that add to their confidence in the GCDH problem. They reach this aim by showing exact relations among the GCDH, GDDH, CDH and DDH problems.
Date: July 20, 2002
Creator: Bresson, Emmanuel; Chevassut, Olivier & Pointcheval, David
Partner: UNT Libraries Government Documents Department

Authenticated group Diffie-Hellman key exchange: theory and practice

Description: Authenticated two-party Diffie-Hellman key exchange allows two principals A and B, communicating over a public network, and each holding a pair of matching public/private keys to agree on a session key. Protocols designed to deal with this problem ensure A (B resp.)that no other principals aside from B (A resp.) can learn any information about this value. These protocols additionally often ensure A and B that their respective partner has actually computed the shared secret value. A natural extension to the above cryptographic protocol problem is to consider a pool of principals agreeing on a session key. Over the years several papers have extended the two-party Diffie-Hellman key exchange to the multi-party setting but no formal treatments were carried out till recently. In light of recent developments in the formalization of the authenticated two-party Diffie-Hellman key exchange we have in this thesis laid out the authenticated group Diffie-Hellman key exchange on firmer foundations.
Date: October 3, 2002
Creator: Chevassut, Olivier
Partner: UNT Libraries Government Documents Department