AffiliationUniv Arizona, Coll Opt Sci
Univ Arizona, Steward Observ
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PublisherSPIE-INT SOC OPTICAL ENGINEERING
CitationDae Wook Kim ; Chang-jin Oh ; Andrew Lowman ; Greg A. Smith ; Maham Aftab and James H. Burge " Manufacturing of super-polished large aspheric/freeform optics ", Proc. SPIE 9912, Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation II, 99120F (July 22, 2016); doi:10.1117/12.2232237; http://dx.doi.org/10.1117/12.2232237
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AbstractSeveral next generation astronomical telescopes or large optical systems utilize aspheric/freeform optics for creating a segmented optical system. Multiple mirrors can be combined to form a larger optical surface or used as a single surface to avoid obscurations. In this paper, we demonstrate a specific case of the Daniel K. Inouye Solar Telescope (DKIST). This optic is a 4.2 m in diameter off-axis primary mirror using ZERODUR thin substrate, and has been successfully completed in the Optical Engineering and Fabrication Facility (OEFF) at the University of Arizona, in 2016. As the telescope looks at the brightest object in the sky, our own Sun, the primary mirror surface quality meets extreme specifications covering a wide range of spatial frequency errors. In manufacturing the DKIST mirror, metrology systems have been studied, developed and applied to measure low-to-mid-to-high spatial frequency surface shape information in the 4.2 m super-polished optical surface. In this paper, measurements from these systems are converted to Power Spectral Density (PSD) plots and combined in the spatial frequency domain. Results cover 5 orders of magnitude in spatial frequencies and meet or exceed specifications for this large aspheric mirror. Precision manufacturing of the super-polished DKIST mirror enables a new level of solar science.
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Adaptive, Dynamic Surface / Wavefront Metrology and AnalysisKim, Dae Wook; Aftab, Maham; Smith, Gregory A.; Liang, Rongguang; Mahajan, Virendra N. (The University of Arizona., 2019)The demand for increasingly sophisticated optics continues to grow for a wide variety of applications, such as in astronomy, industrial manufacturing, medical imaging, and commercial photography. As more advanced fabrication methods are invented, especially for high-resolution or freeform designs, the tools and techniques for optical metrology and analysis must be made more precise, efficient, and robust. This study discusses various approaches for adaptive and dynamic surface or wavefront metrology and analysis which would aid in the ability to have more advanced and innovative optics. Three techniques for improving optical testing and analysis are discussed in this work. The first two are mathematical frameworks, applied in software codes that provide new and improved solutions to challenges arising during optical metrology, e.g., deflectometry measurements and data analysis. Both are based on polynomial basis sets, and are optimized for systems with rectangular apertures. The first is used for reconstructing surfaces or wavefronts from measured slope data and the second uses the measured data to obtain information about possible misalignments or systematic errors in metrology systems. The third is the development of a sensor for measuring wavefront slope data, which allows solutions for optical testing and analysis problems that occur from a limited dynamic range of measurements. The dynamic range of measurement is the range of wavefront slope values (largest and smallest values) that can be measured by a system. The aforementioned sensor uses the modal data fitting methodology described in this work. Each of these topics has been researched, their main concepts tested, and software and (where applicable) hardware solutions developed for them. Simulations and real data analysis are used for verification of these tools and techniques.
Ultra-Precision Non-Contact Metrology for Optical Shop and Alignment ApplicationsLiang, Rongguang; Khreishi, Manal A.; Schwiegerling, James; Kupinski, Matthew (The University of Arizona., 2019)New, unconventional designs for modern optical systems strive for superior performance at lower cost and volume. These compact optical instruments, with larger fields of view and faster f-numbers, call for more challenging prescriptions to meet their ambitious requirements. Freeform optical surfaces have the potential to enable these compact, high-performance systems, but are more challenging to characterize and hence to fabricate. This work enables the use of precision coordinate measuring machine (CMM) for a wide range of optical testing and alignment applications, including the testing and integration of freeform and aspheric optics. In this dissertation, the capabilities of this non-contact, precision metrology instrument have been stretched beyond its everyday applications. Advanced data collection and reduction techniques have been developed to determine the as-built prescription of optical surfaces, as well as the alignment with respect to the part and global coordinate systems. For measurement of low-order surface error and prescription parameters, when compared to interferometry and other optical shop techniques that rely on optical path difference or slope error, these techniques have greater dynamic range and, in some cases, precision that approaches the sensitivity of traditional methods. For example, the CMM, when equipped with a non-contact probe that utilizes a chromatic confocal principle, has a dynamic range measured in mm, a sensitivity measured in nm, yet does not require a null corrector or other custom-made components. In one case, the CMM was used to measure the surface error and as-built prescriptions of two freeform mirrors for a reflective telescope. The CMM was then utilized to align the telescope, as confirmed by an end-to-end interferometric test used to evaluate the system performance. In another example, the CMM was paired with a laser radar (LR) to align a different telescope that uses off-axis, polynomial aspheres in a three mirror anastigmat (TMA) configuration. The CMM enables fast determination of as-built prescription parameters and surface error without the types of systematic errors that are inherent in some traditional optical test setups, like the removal of power or other aberration from alignment of the test setup. The applicability of this work was further studied for large, convex aspheres using the spare secondary mirror for the Hubble Space Telescope (HST) and, via simulation, for large meter-class optics such as the Giant Magellan Telescope (GMT) secondary mirror segments. This measurement technique was further extended to other types of optical surfaces, like gratings and spatial filters. In the case of gratings, it is shown that one can derive as-built period, amplitude, and grating vector quickly and accurately from a few, fast scans.
Adaptive optics capabilities at the Large Binocular Telescope ObservatoryChristou, J. C.; Brusa, G.; Conrad, A.; Esposito, S.; Herbst, T.; Hinz, P.; Hill, J. M.; Miller, D. L.; Rabien, S.; Rahmer, G.; et al. (SPIE-INT SOC OPTICAL ENGINEERING, 2016-07-26)We present an overview of the current and future adaptive optics systems at the LBTO along with the current and planned science instruments they feed. All the AO systems make use of the two 672 actuator adaptive secondary mirrors. They are (1) FLAO (NGS/SCAO) feeding the LUCI NIR imagers/spectrographs; (2) LBTI/AO (NGS/SCAO) feeding the NIR/MIR imagers and LBTI beam combiner; (3) the ARGOS LGS GLAO system feeding LUCIs; and (4) LINO-NIRVANA - an NGS/MCAO imager and interferometer system. AO performance of the current systems is presented along with proposed performances for the newer systems taking into account the future instrumentation.