Optical telescope systems with segmented mirrors require precise coalignment of their segments to achieve the
desired full near-diffraction-limit performance. The segment vertical misalignment (piston error) between the
segments must be reduced to a small fraction of the wavelength (<100nm) of incoming light. We have considered
an interferometric piston error measurement system based on a high-aperture Michelson interferometer layout for
accomplishing such objectives, The piston error between the segments can be extracted from the interferometric
fringes mismatching, The innovation introduced in the optical design of the interferometer is the simultaneous use
of monochromatic light and two-wavelength combination white-light source in a direct method for improving the
central fringe identification in the white-light interferometric phasing system. We find that this two-wavelength
combination technique can greatly increase the visibility difference between the central fringe and its adjacent side
fringes, and thus it offers an increased signal resolution. So make the central fringe identification become easier,
and enhance the measure precision of the segment phasing error. As a result, it is suitable for high-precision
measurement purpose and application in the segment piston error phasing system.
For the optical system of the telescope, with the increase in telescope size, the manufacture of monolithic primary
becomes increasingly difficult. Instead, the use of segmented mirrors, where many individual mirrors (the segments)
work together to provide an image quality and an aperture equivalent to that of a large monolithic mirror, is considered a
more appropriate strategy. But with the introduction of the large telescope mirror comprised of many individual
segments, the problem of insuring a smooth continuous mirror surface (co-phased mirrors) becomes critical. One of the
main problems is the measurement of the vertical displacement between the individual segments (piston error), for such
mirrors, the segment vertical misalignment (piston error) between the segments must be reduced to a small fraction of
the wavelength (<100nm) of the incoming light. The measurements become especially complicated when the piston error
is in order of wavelength fractions. To meet the performance capabilities, a novel method for phasing the segmented
mirrors optics system is described. The phasing method is based on a high-aperture Michelson interferometer. The use of
an interferometric technique allows the measuring of segment misalignment during the daytime with high accuracy,
which is a major design guideline. The innovation introduced in the optical design of the interferometer is the
simultaneous use of monochromatic light and multiwavelength combination white-light source in a direct method for
improving the central fringe identification in the white-light interferometric phasing system. With theoretic analysis, we
find that this multiwavelength combination technique can greatly increase the visibility difference between the central
fringe and its adjacent side fringes, and thus it offers an increased signal resolution. So make the central fringe
identification become easier, and enhance the measure precision of the segment phasing error. Consequently, it is
suitable for high-precision measurement purpose and application in the segment piston error phasing system. The
description about the expected interferograms and the feasibility of the phasing method are presented here.
The quest for higher angular resolution in astronomy will inevitably require the telescope with large aperture. However,
the diameter of primary mirror is limited by the fabrication problems as well as the scaling laws of manufacturing costs.
Optical synthetic aperture telescopes represent a promising new technology to overcome the above-mentioned problems.
Three incoherent imaging techniques based on optical synthetic aperture including Fourier telescopy, Michelson
interferometer and Fizeau interferometer are described in the paper. Fourier telescopy is an active imaging technique
combined with the advantages of synthetic aperture measurement. Michelson interferometers measure spatial Fourier
transform of objects, while Fizeau interferometers produce direct images with full instant frequency coverage. We give
an overview of the basic aspects and the differences of these techniques.
With the increase of telescope size, the manufacture of monolithic primaries becomes increasingly difficult. Instead, the
use of segmented mirrors, where many individual mirrors (the segments) work together to provide good image quality
and an aperture equivalent to that of a large monolithic mirror, is considered a more appropriate strategy. But, with the
introduction of large telescope mirror comprised of many individual segments, the problem of insuring a smooth
continuous mirror surface (co-phased mirrors) becomes critical. One of the main problems arising in the co-phasing of
the segmented mirrors telescope is the problem of measurements of the vertical displacements between the individual
segments (piston errors). Because of such mirrors to exhibit diffraction-limited performance, a phasing process is
required in order to guarantee that the segments have to be positioned with an accuracy of a fraction of a wavelength of
the incoming light.The measurements become especially complicated when the piston error is in order of wavelength
fractions. To meet the performance capabilities, a novel method for phasing the segmented mirrors optical system is
described. The phasing method is based on a high-aperture Michelson interferometer. The use of an interferometric
technique allows the measurement of segment misalignment during daytime with high accuracy, which is a major design
guideline. The innovation introduced in the optical design of the interferometer is the simultaneous use of both
monochromatic and white-light sources that allows the system to measure the piston error with an uncertainty of 6nm in
50µm range. The description about the expected monochromatic and white-light illumination interferograms and the
feasibility of the phasing method are presented here.
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