Phasing the mirror segments of the Keck telescopes: the broadband phasing algorithm

Chanan, G. A.; Troy, Mitchell; Dekens, Frank; Michaels, Scott; Nelson, Jerry; Mast, Terry S.; Kirkman, David

doi:10.1364/ao.37.000140

Cited by 208 publications

(98 citation statements)

References 6 publications

(9 reference statements)

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“…To directly measure each segment, the Shack-Hartmann test [6] and curvature sensor [7,8] have been adapted for alignment. The Shack-Hartmann test is sensitive in a tip-tilt measurement, but it measures wavefront slopes (not surface slopes) at a certain conjugate plane and it is insensitive to local piston errors.…”

Section: Introductionmentioning

confidence: 99%

Simultaneous multi-segmented mirror orientation test system using a digital aperture based on sheared Fourier analysis

et al. 2017

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This paper presents a simultaneous multi-segmented mirror orientation test system (SMOTS) using localized sheared images. A CMOS camera captures images of reflected 2D sinusoidal patterns from the test mirrors as their orientation changes. Surface orientation is measured to within 0.8 µrad (0.16 arcseconds) for a flat mirror. In addition, we measure the variation of seven mirror segments simultaneously. Furthermore, SMOTS is applied to measure the orientation of two concave mirrors with an accuracy of 2.7 µrad (0.56 arcseconds). The measurement time for seven segments is 0.07 s. This technique can monitor the mirror segment orientation in an open/closed-loop for various optical setups. by the use of two parallel interference patterns," Appl. Opt. 36(25), 6190-6195 (1997). 11. J. Yuan and X. Long, "CCD-area-based autocollimator for precision small-angle measurement," Rev. Sci.

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Section: Introductionmentioning

confidence: 99%

Simultaneous multi-segmented mirror orientation test system using a digital aperture based on sheared Fourier analysis

et al. 2017

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“…Using these techniques, the capture range can be extended from the half-wave limitation to a few tens of µm (typically up to 10 µm) upon the method selected (e.g., Chanan et al 1998;Vigan et al 2011;Surdej 2011). Another method exploiting the coherence signature introduced by a liquid crystal tunable filter (Bonaglia et al 2008) shows an even greater capture range (50 µm).…”

Section: Discussionmentioning

confidence: 99%

“…Because the characteristic scale of the measured coherence function is the coherence length of the optical filter, the selection of the optical filter bandpass (δλ F ) is critical to match the range of piston errors that is expected to occur at the expense of precision, and vice versa. This method has been validated with several cophasing sensors with carefully selected bandpasses (e.g., Chanan et al 1998;Surdej 2011). …”

Section: Coherence Methodsmentioning

confidence: 99%

Laser-guide-stars used for cophasing broad capture ranges

Martínez

Janin-Potiron

2016

A&A

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Context. Segmented primary mirrors are indispensable to master the steady increase in spatial resolution. Phasing optics systems must reduce segment misalignments to guarantee the high optical quality required for astronomical science programs. Aims. Modern telescopes routinely use adaptive optics systems to compensate for the atmosphere and use laser-guide-stars to create artificial stars as bright references in the field of observation. Because multiple laser-guide-star adaptive optics are being implemented in all major observatories, we propose to use man-made stars not only for adaptive optics, but for phasing optics. Methods. We propose a method called the doublet-wavelength coherence technique (DWCT), exploiting the D lines of sodium in the mesosphere using laser guide-stars. The signal coherence properties are then used. Results. The DWCT capture range exceeds current abilities by a factor of 100. It represents a change in paradigm by improving the phasing optics capture range from micrometric to millimetric. It thereby potentially eliminates the need of a man-made mechanical pre-phasing step. Conclusions. Extremely large telescopes require hundreds of segments, several of which need to be substituted on a daily basis to be recoated. The DWCT relaxes mechanical integration requirements and speeds up integration and re-integration process.

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“…Some of these methods have been used to detect the piston errors in two-beam CBC [15,17] . For a multi-aperture case, the Hartmann sensor is first applied to phase the 36 primary mirror segments in Keck telescopes [16] . A simulation work [18] demonstrates the application of a Hartmann sensor in multi-beam CBC.…”

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confidence: 99%

“…The piston detection method is similar to the technique used in [16] . The location of the peak intensity of the interference pattern changes with the piston error.…”

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confidence: 99%

Experimental research on application of Hartmann micro-lens array in coherent beam combination of two-dimensional laser array

Wang

Huang

et al. 2012

中国光学快报

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We demonstrate experimentally the application of a phase error detection method in the coherent beam combination (CBC) of a laser array. The method is based on the Hartmann micro-lens array. Both the piston and tilt errors can be detected and corrected simultaneously by combining this method with adaptive optics-correcting technology. The far-field intensity pattern of the combined beam has high energy concentration and good beam quality. The power encircled in the main lobe of the far-field pattern is 41.3%, and the contrast of the pattern reaches 81.8%. Experimental results show the great potential of the Hartmann phasing method for use in the CBC of a large number of laser beams.OCIS codes: 140.3298, 110.1080, 120.5050. doi: 10.3788/COL201210.081402.The coherent beam combination (CBC) of single mode lasers is a reliable method to acquire high-power or high-brightness beams with good beam qualities. Compared with the single high-power lasers, combining several low-power laser beams coherently has advantages in terms of thermal loading distribution and reduction of the diffraction angle. The coherent combining approaches can be classified mainly into active phasing [1−5] and passive phasing [6−9] . The active phasing is mostly based on the master oscillator power amplifier (MOPA) configuration [2−4] , in most of which the fiber phase modulators are inserted before the fiber amplifiers to compensate for the piston aberrations. In some other configurations, the adaptive optics (AO) technologies, such as active segmented mirror (ASM) [5,10] and adaptive photonics phase-locked elements (APPLE) [11] , are employed to perform this task. In addition, the steering mirrors and deformable mirrors can be used to correct tiptilt and higher-order aberrations, respectively [2] . Some of the active phasing methods, such as heterodyne [2,12] and zero-order interference (ZOI) detections, need an external reference beam, while others do not, such as SelfSynchronous and Self-Reference [3] and SPGD algorithm control [4,11] . Most of these techniques extract the phase errors from the signals coming from the photo-detectors with a pinhole. Another type of phasing method [13−16] is applied in phasing large segmented telescopes in order to detect the piston errors between two neighboring apertures or segmented mirrors. These methods measure the piston errors by processing the interference images of the two apertures. Some of these methods have been used to detect the piston errors in two-beam CBC [15,17] . For a multi-aperture case, the Hartmann sensor is first applied to phase the 36 primary mirror segments in Keck telescopes [16] . A simulation work [18] demonstrates the application of a Hartmann sensor in multi-beam CBC. In these applications, Hartmann sensors are employed to acquire the interference images of two neighboring apertures or beams. Apart from piston error detection, the Hartmann sensor can also perform tilt error detection simultaneously.In this letter, we demonstrate experimentally the method of piston and ti...

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Phasing the mirror segments of the Keck telescopes: the broadband phasing algorithm

Cited by 208 publications

References 6 publications

Simultaneous multi-segmented mirror orientation test system using a digital aperture based on sheared Fourier analysis

Simultaneous multi-segmented mirror orientation test system using a digital aperture based on sheared Fourier analysis

Laser-guide-stars used for cophasing broad capture ranges

Experimental research on application of Hartmann micro-lens array in coherent beam combination of two-dimensional laser array

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