Phase-diversity wave-front sensing with a distorted diffraction grating

Blanchard, Pierrette; Fisher, David J.; Woods, Simon C.; Greenaway, A. H.

doi:10.1364/ao.39.006649

Cited by 74 publications

(27 citation statements)

References 7 publications

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“…The principle of operation of Distorted Grating WFS (DGWFS) is described in detail in [11][12][13] and only essential information will be given here. The DGWFS relies on the Intensity Transport Equation, Eq.…”

Section: Dgwfs Principle Of Operation and Data Reductionmentioning

confidence: 99%

See 1 more Smart Citation

Hybrid Flow Control of a Turret Wake, Part II: Aero-Optical Effects

Gordeyev

Jumper

Vukašinović

et al. 2010

48th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition

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This paper presents the optical results of using combined passive and active flow control to improve the aero-optical environments around a conformal-window, hemisphere-oncylinder turret. Several wavefront sensors were used to directly measure optical distortions at several back-looking angles. It was shown that the hybrid flow control significantly reduces levels of optical distortions for elevation angles as high as 148 degrees at M = 0.3. The paper also devotes considerable attention to overcoming environmental conditions present in large-scale wind tunnels. I. BackgroundN the last decade or so the research in using turrets to transmit laser beams from subsonic airborne platforms has greatly intensified. While a turret provides a convenient mechanical system to point-and-track the laser beam, the wake flow behind this bluff-body turret is both turbulent and complex with many vortical structures present. These structures are known to create significant density gradients and related aero-optical distortions 1 when the laser beam is transmitted through the wake of the turret even at low transonic speeds (see [2] and references therein, for instance). Left untreated, these detrimental aero-optical effects greatly reduce the laser-beam intensity in the farfield.An earlier investigation of the optical environment around a one-foot conformal-window turret for the range of the elevation angles between 60 and 132 degrees 3 in the zenith plane showed the level of optical distortions increases for backward looking angles above 120 degrees. To measure optical aberrations at higher elevation angles and investigate strategies to mitigate these large levels of optical distortions at high back-looking angles, as well to address Reynolds number effects and scaling issues, a two-foot conformal window turret was tested for a range of back-looking angles from 129 to 149 degrees and Mach numbers between 0.3 and 0.5 4,5 . The turret was instrumented with static ports to measure the location of the flow separation line. Velocity profiles in the wake downstream of the turret were measured using a single hot-wire and the surface flow topology was studied with oil flow visualization. Optical measurements were performed using a Malley Probe. In order to study the mitigating effects of active flow control the turret was equipped with an array of synthetic jets upstream of the window aperture. In previous studies these actuators were shown to be effective in suppressing turbulence behind a bluffbody turret at Re D = 8·105 [6], as well as behind a 10-inch hemispherical turret 7 , where significant suppression of turbulent fluctuations and reduction in optical distortions were observed up to M = 0.45. The array of synthetic jets introduces small-scale, highly dissipative structures into the attached boundary layer upstream of the window aperture. This flow actuation was shown to lead to flow-separation delay on the window's surface; up to a 10-degree delay in separation was observed to an elevation angle of 139 degrees 4 . A broad-band sup...

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Section: Dgwfs Principle Of Operation and Data Reductionmentioning

confidence: 99%

“…(2)). One way to simultaneously record intensities at two different z-planes is to use a quadratic grading combined with a lens [11], see Figure 7. It creates a pair of images corresponding to beam intensities at known distances z 1 and z 2 which are defined by the lens-grating geometry.…”

Section: Dgwfs Principle Of Operation and Data Reductionmentioning

confidence: 99%

Hybrid Flow Control of a Turret Wake, Part II: Aero-Optical Effects

Gordeyev

Jumper

Vukašinović

et al. 2010

48th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition

View full text Add to dashboard Cite

show abstract

“…Recent implementations of the phase-diversity approach have used Diffractive Optical Elements (DOEs) known as IMPs (IMP is a trademark of QinetiQ Ltd). This particular implementation has the disadvantage that the use of the DOE restricts it to an optical bandpass but the corrected image and the wavefront sensor data can be delivered to a common detection plane, reducing the likelihood of non-common-path errors (Blanchard et al 2000). The principles of these wavefront sensors are best explained by considering the operation in the plane of the objective lens (figure 4).…”

Section: Phase-diversity and Curvature Sensorsmentioning

confidence: 99%

Smart optics in ast

Welch¹,

Greenaway

Doel³

et al. 2003

Astron Geophys

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S mart optics is a developing field that includes active and adaptive optics, applications becoming familiar in astronomy. Many of the largest ground-based telescopes use wavefront sensors to analyse the distortion of signals by the atmosphere, and wavefront modulators such as deformable mirrors to compensate for these effects. But these techniques can also greatly enhance the use of telescopes and other instruments in space, improve the resolution of Earth-observing and planetary-exploration satellites, for example, and even bring new precision to formation flying by satellites.The term adaptive optics (AO) has become particularly associated with systems on large telescopes used to compensate for the deleterious effects of the atmosphere. AO systems measure the shape of the wavefronts of the incoming light (or that of an artificial laser guide-star in the field) and use a wavefront modulator to correct the wavefronts before they reach the sensor (figure 1). In general, a system that can dynamically adjust, or be part of a complex control loop, is better and more flexible. Smart optics technologiesIn this simple description, smart optics depends on two technologies: G A wavefront modulator, which can modify the shape of an incoming wavefront (thus changing its phase). Examples include deformable mirrors and liquid-crystal lenses. G A wavefront sensor, which can estimate the shape of the wavefront. These use, for example, lenslet arrays and phase-diversity measurements.These two essential building blocks are linked together in an AO system through a control loop to modify the incoming wavefronts, but the basic technologies of the wavefront modulators and the wavefront sensors have other "smart" applications that do not necessarily require linkage. In the following sections we will consider briefly some of the approaches used, first in wavefront modulation and then in wavefront sensing, with particular emphasis on developments that are supported through the Smart Optics Faraday Partnership in the UK and their application beyond terrestrial astronomy. Deformable mirror technologyIn present telescope AO systems the most commonly used wavefront modulator is a deformable mirror. Many types are in use, with such technology as thin glass facesheets deformed by piezoelectric actuators; bimorph mirrors made of thin slabs of piezoelectric material; and membrane mirrors that depend on electrostatic distortion of a thin metallic membrane. These mirrors range from a few centimetres to a few tens of centimetres across. A recent innovation in deformable mirrors has been the development of micro-mirrors manufactured using Micro-Electro Mechanical Systems (MEMS) technology. The mirror is made using techniques developed from silicon chip production, where micro-electromechanical actuators are produced on a silicon wafer using photo-lithography and etching. This technology has already found uses in the optical switching and projection markets and has the potential to produce mirrors with thousands of tiny actuators at relatively l...

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“…If only the coefficient of each Zernike aberration mode is fixed, we will retrieve the aberration in formation and fully reconstruct the distorted wavefront. Various techniques exist in the literature for wavefront sensing [2]- [4], each with their own benefits and drawbacks. Recently, a holographic wavefront sensor has been proposed [5], [6], in which a multiplexed hologram acts as a wavefront sensor.…”

Section: Introductionmentioning

confidence: 99%

Extraction of Zernike Coefficients Modes using Holographic Wavefront Sensing: Modeling and Simulation

Mohammed¹,

Bahloul²,

Cherif³

et al. 2015

IJIEE

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Abstract-We propose a holographic wavefront sensor that uses a binary computer-generated hologram (BCGH). This CGH is coded with a single particular Zernike aberration mode with different coeffecients and then all the holograms are multiplexed and binarized to get the final hologram. This multiplexed hologram is used to produce a spots (white pixel on the detector) according to the presence of particular aberration. The Numerical results by Matlab program corresponding to the CGHs are presented.

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Phase-diversity wave-front sensing with a distorted diffraction grating

Cited by 74 publications

References 7 publications

Hybrid Flow Control of a Turret Wake, Part II: Aero-Optical Effects

Hybrid Flow Control of a Turret Wake, Part II: Aero-Optical Effects

Smart optics in ast

Extraction of Zernike Coefficients Modes using Holographic Wavefront Sensing: Modeling and Simulation

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