A. Kritcher, D. Schlossberg, C. Weber, C. Young, E. Dewald, A. Zylstra, O. Hurricane, A. Allen, B. Bachmann, K. Baker, S. Baxamusa, T. Braun, G. Brunton, D. Callahan, D. Casey, T. Chapman, C. Choate, D. Clark, J.-M. Di Nicola, L. Divol, M. Edwards, S. Haan, T. Fehrenbach, S. Hayes, D. Hinkel, M. Hohenberger, K. Humbird, O. Jones, E. Kur, B. Kustowski, C. Kong, O. Landen, D. Larson, X. Lepro-Chavez, J. Lindl, B. MacGowan, S. Maclaren, M. Marinak, M. Millot, A. Nikroo, R. Nora, A. Pak, P. Patel, J. Ralph, M. Ratledge, M. Rubery, S. Sepke, M. Stadermann, D. Strozzi, T. Suratwala, R. Tommasini, R. Town, B. Woodworth, B. Van Wonterghem, C. Wild
An exciting use of high powered lasers is to inertially confine fusion plasmas in the laboratory. This presentation describes the first design to achieve controlled fusion target gain exceeding one using high powered lasers in the inertial confinement fusion approach and recent experimental results on the NIF (National Ignition Facility). In these experiments, laser beams incident on the inside of a cylindrical can (Hohlraum) generates an intense x-ray radiation bath that is used to spherically implode pellets containing Deuterium and Tritium. On Dec 5th 2022, the imploded pellet generated more fusion energy (3.15 MJ) than laser energy incident on the target (2.05 MJ), reaching a milestone for the field that was more than six decades in the making. Follow on experiments in this platform using 2.2 MJ of laser energy have generated >5 MJ and >2x target gain.
Phase reconstructions from a two-dimensional shearing interferometer, based on two orthogonal phase gratings in a single plane, and a Hartmann sensor are compared. Design alternatives for both wavefront sensors are given, and simulated performance of both the two-dimensional x-ray shearing interferometer and Hartmann wavefront sensor are presented for two different phase profiles. The first comparison is an evaluation of metrology on deuterium-tritium (DT) ice layers in an inertial confinement fusion capsule, and the second comparison is a high frequency “asterisk” phase profile, which tests the ability of these wavefront sensors to detect spikes of ablator material seen in DT fuel capsule implosions. Both of these sensors can measure the two-dimensional wavefront gradient of an x-ray beam, as well as the x-ray absorption. These instruments measure the two-dimensional wavefront gradient in a single measurement, and the wavefront sensor is located in a single plane, making them much less sensitive to vibrations than most other wavefront sensing techniques.
Phase reconstructions from a two-dimensional shearing interferometer, based on two orthogonal phase gratings in a single plane, and a Hartmann sensor are compared. Design alternatives for both wavefront sensors are given and simulated performance of both the two-dimensional x-ray shearing interferometer and Hartmann wavefront sensor are presented for two different phase profiles. The first comparison is an evaluation of metrology on DT ice layers in an inertial confinement fusion capsule and the second comparison is a high frequency "asterisk" phase profile. Both of these sensors can measure the two-dimensional wave-front gradient of an x-ray beam, as well as the x-ray absorption. These instruments measure the two-dimensional wave-front gradient in a single measurement and the wavefront sensor is located in a single plane making them much less sensitive to vibrations than most other wavefront sensing techniques.
Mina Bionta, Doug French, James Cryan, James Glownia, Nick Hartmann, David Nicholson, Kevin Baker, Christoph Bostedt, Marco Cammarrata, Matthieu Chollet, Yuantao Ding, David Fritz, Steve Durbin, Yiping Feng, Marion Harmand, Alan Fry, Daniel Kane, Jacek Krzywinski, Henrik Lemke, Marc Messerschmidt, Daniel Ratner, Sebastian Schorb, Sven Toleikis, Diling Zhu, William White, Ryan Coffee
A recently demonstrated single-shot measurement of the relative delay between x-ray FEL pulses and optical laser pulses has now been improved to ~10 fs rms error and has successfully been demonstrated for both soft and hard x-ray pulses. It is based on x-ray induced step-like reduction in optical transmissivity of a semiconductor membrane (Si3N4). The transmissivity is probed by an optical continuum spanning 450 - 650 nm where spectral chirp provides a mapping of the step in spectrum to the arrival time of the x-ray pulse relative to the optical laser system.
This article presents the design and simulated performance of a two-dimensional x-ray shearing interferometer
wavefront sensor. In particular, this phase sensitive x-ray wavefront sensor is evaluated for its ability to perform
metrology on the DT ice layer in an inertial confinement fusion capsule. The interferometer uses crossed phase gratings
in a single plane and is capable of operation over a wide range of x-ray energies by varying the grating material and
thickness. The wave-front sensor is insensitive to vibrations and, unlike X-RayTalbot interferometers, recovers the full
two-dimensional phase profile of the x-ray beam rather than the gradient in only one dimension.
The Large Synoptic Survey Telescope will map out the dark matter in the universe and is scheduled to see "first light" in
2014. This telescope will require active correction of its mirrors to remove the aberrations that arise from changing
gravitational force vectors and from thermal drifts in the telescope during observational runs. In this article we present a
comprehensive evaluation of a Shack-Hartmann wavefront sensor and reconstruction algorithm which is capable of
meeting the unique challenges associated with this wide field-of-view survey telescope. The advantages of this technique
over other potential wavefront sensing technologies are discussed and the potential problems encountered with this
approach are analyzed and solutions to these problems presented.
We present the design and simulations of the expected performance of a novel 2-D x-ray shearing interferometer. This interferometer uses crossed phase gratings in a single plane, and is capable of operation over a wide range of energies extending from several hundred electron volts to tens of kiloelectron volts by varying the grating material and thickness. This interferometer is insensitive to vibrations and, unlike Moiré deflectometers implemented in the hard x-ray regime, recovers the full 2-D phase profile of the x-ray beam rather than the gradient in only one dimension.
Implementing the capability to perform fast ignition experiments, as well as, radiography experiments on the National Ignition Facility (NIF) places stringent requirements on the control of each of the beam's pointing and overall wavefront quality. One quad of the NIF beams, four beam pairs, will be utilized for these experiments and hydrodynamic and particle-in-cell simulations indicate that for the fast ignition experiments, these beams will be required to deliver 50% (4.0 kJ) of their total energy (7.96 kJ) within a 40-µm-diam spot at the end of a fast ignition cone target. This requirement implies a stringent pointing and overall phase conjugation error budget on the adaptive optics system used to correct these beam lines. The overall encircled energy requirement is more readily met by phasing of the beams in pairs but still requires high Strehl ratios and root-mean-square tip/tilt errors of approximately 1 µrad. To accomplish this task we have designed an interferometric adaptive optics system capable of beam pointing, high Strehl ratio, and beam phasing with a single pixilated microelectromechanical systems deformable mirror and interferometric wavefront sensor. We present the design of a testbed used to evaluate the performance of this wavefront sensor along with simulations of its expected performance level.
Implementing the capability to perform fast ignition experiments, as well as, radiography experiments on the National
Ignition Facility (NIF) places stringent requirements on the control of each of the beam's pointing and overall wavefront
quality. One quad of the NIF beams, 4 beam pairs, will be utilized for these experiments and hydrodynamic and
particle-in-cell simulations indicate that for the fast ignition experiments, these beams will be required to deliver
50%(4.0 kJ) of their total energy(7.96 kJ) within a 40 μm diameter spot at the end of a fast ignition cone target. This
requirement implies a stringent pointing and overall phase conjugation error budget on the adaptive optics system used
to correct these beam lines. The overall encircled energy requirement is more readily met by phasing of the beams in
pairs but still requires high Strehl ratios, Sr, and RMS tip/tilt errors of approximately one μrad. To accomplish this task
we have designed an interferometric adaptive optics system capable of beam pointing, high Strehl ratio and beam
phasing with a single pixilated MEMS deformable mirror and interferometric wave-front sensor. We present the design
of a testbed used to evaluate the performance of this wave-front sensor below along with simulations of its expected
performance level.
Several high-contrast imaging systems are currently under construction to enable the detection of extra-solar planets. In
order for these systems to achieve their objectives, however, there is considerable developmental work and testing which
must take place. Given the need to perform these tests, a spatially-filtered Shack-Hartmann adaptive optics system has
been assembled to evaluate new algorithms and hardware configurations which will be implemented in these future
high-contrast imaging systems. In this article, construction and phase measurements of a membrane "woofer" mirror are
presented. In addition, results from closed-loop operation of the assembled testbed with static phase plates are presented.
The testbed is currently being upgraded to enable operation at speeds approaching 500 hz and to enable studies of the
interactions between the woofer and tweeter deformable mirrors.
The two-sided pyramid wavefront sensor has been extensively simulated in the direct phase mode using a wave optics code. The two-sided pyramid divides the focal plane so that each half of the core only interferes with the speckles in its half of the focal plane. A relayed image of the pupil plane is formed at the CCD camera for each half. Antipodal speckle pairs are separated so that a pure phase variation causes amplitude variations in the two images. The phase is reconstructed from the difference of the two amplitudes by transforming cosine waves into sine waves using the Hilbert transform. There are also other corrections which have to be applied in Fourier space. The two-sided pyramid wavefront sensor performs extremely well: After two or three iterations, the phase error varies purely in y. The twosided pyramid pair enables the phase to be completely reconstructed. Its performance has been modeled closed loop with atmospheric turbulence and wind. Both photon noise and read noise were included. The three-sided and four-sided pyramid wavefront sensors have also been studied in direct phase mode. Neither performs nearly as well as does the two-sided pyramid wavefront sensor.
The Large Synoptic Survey Telescope (LSST) is a three mirror modified Paul-Baker design with an 8.4m primary, a
3.4m secondary, and a 5.0m tertiary followed by a 3-element refractive corrector producing a 3.5 degree field of view.
This design produces image diameters of <0.3 arcsecond 80% encircled energy over its full field of view. The image
quality of this design is sufficient to ensure that the final images produced by the telescope will be limited by the
atmospheric seeing at an excellent astronomical site. In order to maintain this image quality, the deformations and rigid
body motions of the three large mirrors must be actively controlled to minimize optical aberrations. By measuring the
optical wavefront produced by the telescope at multiple points in the field, mirror deformations and rigid body motions
that produce a good optical wavefront across the entire field may be determined. We will describe the details of the
techniques for obtaining these solutions. We will show that, for the expected mirror deformations and rigid body
misalignments, the solutions that are found using these techniques produce an image quality over the field that is close to
optimal. We will discuss how many wavefront sensors are needed and the tradeoffs between the number of wavefront
sensors, their layout and noise sensitivity.
Direct detection of extrasolar Jovian planets is a major scientific motivation for the construction of future extremely
large telescopes such as the Thirty Meter Telescope (TMT). Such detection will require dedicated high-contrast AO
systems. Since the properties of Jovian planets and their parent stars vary enormously between different populations, the
instrument must be designed to meet specific scientific needs rather than a simple metric such as maximum Strehl ratio.
We present a design for such an instrument, the Planet Formation Imager (PFI) for TMT. It has four key science
missions. The first is the study of newly-formed planets on 5-10 AU scales in regions such as Taurus and Ophiucus -
this requires very small inner working distances that are only possible with a 30m or larger telescope. The second is a
robust census of extrasolar giant planets orbiting mature nearby stars. The third is detailed spectral characterization of
the brightest extrasolar planets. The final targets are circumstellar dust disks, including Zodiacal light analogs in the
inner parts of other solar systems. To achieve these, PFI combines advanced wavefront sensors, high-order MEMS
deformable mirrors, a coronagraph optimized for a finely- segmented primary mirror, and an integral field spectrograph.
Direct observation of extrasolar Jovian planets will enable detailed investigation and understanding of the formation of these planet populations and also of their relative abundance. Future large telescopes, such as the Thirty Meter Telescope(TMT), will enable the study of such planet populations at relatively small working distances from the parent star. We present an analysis of an extreme adaptive optics system utilizing a self-referencing phase-shifting interferometer as the primary wave-front sensor. A module of the adaptive optics system consists of a conventional Shack-Hartmann wave-front sensor to provide the initial start-up of the adaptive optics system, thereby placing a significant amount of energy into the core of the point spread function which will act as the reference for the primary interferometric wave-front sensor. The interferometric-based wave-front sensor is shown to provide a significant improvement in the achievable contrast ratio compared with conventional adaptive optics systems containing Shack-Hartmann wave-front sensors.
This article investigates the use of a multi-conjugate adaptive optics system to improve the field-of-view for the system. The emphasis of this research is to develop techniques to improve the performance of optical systems with applications to horizontal imaging. The design and wave optics simulations of the proposed system are given. Preliminary results from the multi-conjugate adaptive optics system are also presented. The experimental system utilizes a liquid-crystal spatial light modulator and an interferometric wave-front sensor for correction and sensing of the phase aberrations, respectively.
Horizontal path correction of optical beam propagation presents a severe challenge to adaptive optics systems due to the short transverse coherence length and the high degree of scintillation incurred by propagation along these paths. The system presented operates with nearly monochromatic light. It does not require a global reconstruction of the phase, thereby eliminating issues with branch points and making its performance relatively unaffected by scintillation. The systems pixel count, 1024, and relatively high correction speed, in excess of 800 Hz, enable its use for correction of horizontal path beam propagation. We present results from laboratory and field tests of the system in which we have achieved Strehl ratios greater than 0.5.
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