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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Using the Gerchberg-Saxton algorithm to reconstruct nonmodulated pyramid wavefront sensor measurements

Adaptive optics (AO) is a technique to improve the resolution of ground-based telescopes by correcting, in real-time, optical aberrations due to atmospheric turbulence and the telescope itself. With the rise of Giant Segmented Mirror Telescopes (GSMT), AO is needed more than ever to reach the full potential of these future observatories. One of the main performance drivers of an AO system is the wavefront sensing operation, consisting of measuring the shape of the above mentioned optical aberrations. Aims. The non-modulated pyramid wavefront sensor (nPWFS) is a wavefront sensor with high sensitivity, allowing the limits of AO systems to be pushed. The high sensitivity comes at the expense of its dynamic range, which makes it a highly non-linear sensor. We propose here a novel way to invert nPWFS signals by using the principle of reciprocity of light propagation and the Gerchberg-Saxton (GS) algorithm. We test the performance of this reconstructor in two steps: the technique is first implemented in simulations, where some of its basic properties are studied. Then, the GS reconstructor is tested on the Santa Cruz Extreme Adaptive optics Laboratory (SEAL) testbed located at the University of California Santa Cruz. This new way to invert the nPWFS measurements allows us to drastically increase the dynamic range of the reconstruction for the nPWFS, pushing the dynamics close to a modulated PWFS. The reconstructor is an iterative algorithm requiring heavy computational burden, which could be an issue for real-time purposes in its current implementation. However, this new reconstructor could still be helpful in the case of many wavefront control operations. In conclusion, this reconstruction technique has also been successfully tested on the Santa Cruz Extreme AO Laboratory (SEAL) bench where it is now used as the standard way to invert nPWFS signal.

47 OTHER INSTRUMENTATION↗
DOE OSTI2018

Investigation of an apodized imaged Hartmann wavefront sensor

Here, quantitative wavefront measurements are demonstrated using a Hartmann mask re-imaged onto a camera. The wavefront is reconstructed using standard algorithms applied to the difference of beamlet centroids determined from fluence distributions obtained for two different longitudinal locations of the mask. The wavefront of the optical wave in the object plane is measured independently of imaging-system collimation. Apodization obtained with spatially dithered distributions of small transparent or opaque pixels improves the measurement accuracy by reducing the spatial-frequency content of the mask holes. Simulations and experiments demonstrate the excellent accuracy of this diagnostic over a wide range of parameters, making it suitable, for example, to characterize laser systems.

47 OTHER INSTRUMENTATION↗
DOE OSTI2023

X-ray wavefront sensor development at the Advanced Light Source

At Lawrence Berkeley National Laboratory's Advanced Light Source, we are developing x-ray wavefront sensors to support the creation and operation of beamlines with diffraction-limited quality. Our new approach to rapid, intermittent wavefront sensing operates in reflection at glancing incidence angles and is compatible with the high-power densities of modern beamlines. For soft x-ray applications especially, the wavefront sensor can operate upstream of the exit slit in a vertically dispersed beam. This single-shot technique supports lateral shearing interferometry and Hartmann wavefront sensing; it can be adapted to speckle-based techniques as well. The reflected beam is directed to an off-axis YAG crystal that produces scintillated visible light. A small mirror reflects the light to a microscope and camera, and the measured wavefront shape information can be used as feedback to adaptive x-ray mirror elements. A compact array of gratings enables measurement across a broad range of photon energies or wavefront curvatures. We describe recent demonstrations at soft x-ray and hard x-ray wavelengths measuring an adaptive x-ray mirror, and a toroidal focusing mirror.

Goldberg, Kenneth A↗
DOE OSTI2021

Binary Amplitude Reflection Gratings for X-ray Shearing and Hartmann Wavefront Sensors

New, high-coherent-flux X-ray beamlines at synchrotron and free-electron laser light sources rely on wavefront sensors to achieve and maintain optimal alignment under dynamic operating conditions. This includes feedback to adaptive X-ray optics. We describe the design and modeling of a new class of binary-amplitude reflective gratings for shearing interferometry and Hartmann wavefront sensing. Compact arrays of deeply etched gratings illuminated at glancing incidence can withstand higher power densities than transmission membranes and can be designed to operate across a broad range of photon energies with a fixed grating-to-detector distance. Coherent wave-propagation is used to study the energy bandwidth of individual elements in an array and to set the design parameters. We observe that shearing operates well over a ±10% bandwidth, while Hartmann can be extended to ±30% or more, in our configuration. We apply this methodology to the design of a wavefront sensor for a soft X-ray beamline operating from 230 eV to 1400 eV and model shearing and Hartmann tests in the presence of varying wavefront aberration types and magnitudes.

47 OTHER INSTRUMENTATION↗
DOE OSTI2018

Design and demonstration of tunable soft x-ray lateral shearing and Hartmann wavefront sensors

We describe design guidelines for soft x-ray wavefront sensors and experimentally demonstrate their performance, comparing grating-based lateral shearing interferometry and Hartmann wavefront sensing. We created a compact shearing interferometer concept with a dense array of binary amplitude gratings in a single membrane to support one-dimensional wavefront measurements across a wide wavelength range without the need for longitudinal position adjustment. We find that a common scaling parameter based on wavelength and the distance to the measurement plane guides the design of both systems toward optimal sensitivity. We show preliminary results from recent experiments demonstrating one and two-dimensional wavefront sensing below the Marechal criterion.

Chao, Weilun↗
DOE OSTI2017

Holographic mode wavefront sensor with an enlarged number of measured modes

A holographic mode wavefront sensor is proposed, which makes it possible to measure up to several tens of wavefront modes. The increase in the number of measured modes is implemented using the conversion of a light wave entering the sensor into a wide diffuse light beam, which allows one to record a large number of holograms, each intended for measuring one of the modes. (holographic sensors)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Holographic wavefront sensors

A brief historical review of the first designs of holographic wavefront sensors (WFS’s) and the concepts lying in their basis is presented. The main directions in the development of these sensors are highlighted and considered. One of these directions implies a two-stage transition from the use of several separate measuring channels with holograms filtering only one Zernike mode: first to the use of one channel with a multiplexed hologram filtering several first Zernike modes, and then to filtering the entire set of Zernike modes with the aid of one combined multiplexed hologram. Another line of research in this field (related to the first one) is the optimisation of the filter hologram structure in order to reduce cross-modulation interferences, increase multiplexing level, etc. One more line of research implements principles of dynamic holography by introducing spatial light modulators into the WFS composition. Hence, the advantages of time multiplexing of holograms can be used. The approach developed by G. Andersen’s team, aimed at adapting the holographic WFS design for operation as an element of adaptive optical system with a zonal corrector, as well as an approach implying development of hybrid holographic sensors, are considered separately. The results of the authors’ studies of holographic WFS’s with application of the methods of Fourier holography (i.e., holography of focused beams, in particular, using diffuse scatterers in a hologram recording channel) are also reported. (paper)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Portable COTS RGB Wavefront Sensor

Atmospheric effects reduce the ability to detect or identify objects of interest due to spatial and spectral scintillation. Algorithms alone cannot correct for turbulence over long-range horizontal paths. While adaptive optics (AO) work well for astronomical viewing, the same methods do not adapt directly for complex imagery over long-range horizontal paths. In this two-year research project, we combine an off-the-shelf high-frame-rate USB3 color camera with a compact 90 mm Maksutov-Cassegrain telescope to create a portable red/green/blue (RGB) wavefront sensor. The 90 mm aperture is covered with an aluminum plate holding three separate narrowband color filters. These filters, specifically matched to the relative spectral response of the sensor’s Bayer mask, provide nearly complete separation of the three color planes. This device enables portable imaging through atmospheric turbulence and analysis thereof, where relative motion of the three-color Bayer-pixel video provides real-time wavefront information on the second-order statistics of Kolmogorov turbulence. We not only extract dwell-averaged wavefront tip and tilt as a function of time but also, using our spectral filtering algorithm, are able to fit higher-order modes to the imaged wavefront statistics. In our second year, we will combine this sensor with a deformable mirror to complete the AO system for long-range horizontal paths.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2024

Control Algorithms for Multi-Wavefront Sensor Adaptive Optics for Astronomical Exoplanet Imaging

This package consists of simulations of control algorithms being proposed for upcoming adaptive optics projects for exoplanet direct imaging, in which one wavefront affector (deformable mirror) is controlled by two wavefront sensors. Simulations include time-domain behavior under various assumed conditions, parameter optimization routines for the controllers, and stability analysis.

Sengupta, Aditya↗
DOE OSTI2026

Control Algorithms for Dual-wavefront Sensor Single-conjugate Adaptive Optics

High-contrast imaging systems using active control with adaptive optics (AO) are often limited by non-common path (NCP) aberrations that are seen only at the final science image. AO systems employing focal-plane wavefront sensors (FP-WFSs) are able to simultaneously correct NCP aberrations and measure science images, but they typically require a second stage of control that adds system cost and complexity. We present control algorithms to augment AO systems with FP-WFSs within their existing control setup. We demonstrate inter-arm NCP aberration transfer can be mitigated through temporal filtering, present frequency- and time-domain validation of controller stability and performance, and discuss the optimality of the chosen controllers. This work will enable the development, testing, and installation of FP-WFS technologies for direct imaging of exoplanets.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Pseudo-gray-scale halftone gratings for shearing and Hartmann wavefront sensors

Now in use on x-ray beamlines worldwide, shearing interferometry and Hartmann wavefront sensing provide effective feedback for measuring and optimizing high-quality beams. Conventionally, both approaches spatially modulate the beam properties (amplitude or phase) using two-tone, binary patterns, leading to deleterious diffraction effects that must be mitigated. In shearing, the presence of multiple diffraction orders affects measurement near boundaries. In Hartmann, diffraction limits the measurement point density. We demonstrate that the use of pseudo-gray-scale halftone patterns in the diffracting elements can improve the performance of both techniques.

47 OTHER INSTRUMENTATION↗
DOE OSTI2016

RGB Wavefront Sensor for Turbulence Mitigation STL-078-16, Year 1 of 2

Presentation to be given at two meetings: (1) The Annual SDRD Final Review, Sept. 22, 2016 in Las Vegas at the Great Basin Nevada Support Facility [website: https://nlv-ddsprd1-ws.nts.ops/SDRD/] and (2) Military Sensing Symposium (MSS) Parallel, Passive Sensors. 31 Oct-4 Nov 2016, Gaithersburg, MD [website: https://www.sensiac.org/external/mss/meetings/list_meetings.jsf;jsessionid=A3885D13D51E3D90C36396CDE7240DAA].

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2021

RGB wavefront sensor for turbulence mitigation

A compact adaptive optics system for long-range horizontal paths imaging that improves degraded images. The system uses a filter that corresponds to the three colors in a typical color detector element, one or more optic elements, a deformable mirror, and a detector. Focus errors, due to turbulence, in the image recorded by the detector element show up as image shifts in the three distinct color images. The shifts and statistics of these shifts between these simultaneous images are used to create control signals for the deformable mirror resulting in a compact adaptive optic system for horizontal paths without need for a point source located at the distance scene being imaged. Analysis of the relative pixel shifts in various regions of the image provides third order statistics revealing tip/tilt and additional Zernikes modes that are used to control a deformable mirror without the need for a guide star/point-source.

O'Neill, Mary Dominique↗
DOE OSTI2020

X-ray free-electron laser wavefront sensing using the fractional Talbot effect

Wavefront sensing at X-ray free-electron lasers is important for quantitatively understanding the fundamental properties of the laser, for aligning X-ray instruments and for conducting scientific experimental analysis. A fractional Talbot wavefront sensor has been developed. This wavefront sensor enables measurements over a wide range of energies, as is common on X-ray instruments, with simplified mechanical requirements and is compatible with the high average power pulses expected in upcoming X-ray free-electron laser upgrades. Single-shot measurements were performed at 500 eV, 1000 eV and 1500 eV at the Linac Coherent Light Source. These measurements were applied to study both mirror alignment and the effects of undulator tapering schemes on source properties. The beamline focal plane position was tracked to an uncertainty of 0.12 mm, and the source location for various undulator tapering schemes to an uncertainty of 1m, demonstrating excellent sensitivity. These findings pave the way to use the fractional Talbot wavefront sensor as a routine, robust and sensitive tool at X-ray free-electron lasers as well as other high-brightness X-ray sources.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗