Chueh Ting, Michael K. Giles, David G. Voelz ... the need for adaptive optics for a long-baseline optical interferometer operating in the turbulent atmosphere.
Adaptive Optics ——————————————— Effectiveness of High-Order Adaptive Optics in Ground-Based Stellar Interferometry Chueh Ting, Michael K. Giles, David G. Voelz ABSTRACT The ground-based optical interferometer with large apertures is a potential research tool for the study of stellar astrophysics and the synthesis of high-resolution stellar images. However, atmospheric turbulence can impose a significant limitation on the interferometer's performance. In order to reduce those degrading effects, we investigate the effectiveness of high-order adaptive optics in ground-based optical interferometry. The purposes of this paper are (1) to evaluate the performance with and without using high-order adaptive optics in a ground-based optical interferometer with large-aperture telescopes, and (2) to investigate the possibility of using the Strehl ratio to estimate visibility. The theoretical methodology and computer simulation results used to evaluate the performance of a ground-based stellar interferometer with high-order adaptive optics are presented, and a numerical computational method that uses the Strehl ratio to estimate the mean squared atmospheric coherence loss factor is developed. Optical Engineering 45(02), 026001, Feb 2006
NMSU EORL Adaptive Optics Testbed and its Performance Evaluation C. Ting, M. K. Giles ABSTRACT In this paper, we present a novel adaptive optics testbed and its performance evaluation procedures. The testbed was built in the New Mexico State University (NMSU) Electro-optics Research Laboratory (EORL). NMSU's EORL adaptive optics testbed includes a tip-tilt error compensation system and a higher-order phase aberration compensation system. The tip-tilt error compensation was completed using a fast steering mirror with a quadrant cell detector. The higher-order phase aberration compensation was achieved using a 37-actuator deformable mirror and image sharpness with a stochastic parallel gradient descent algorithm (SPGDA). A metric optimization process was added in the SPGDA to fit an 8-bit deformable mirror control card. The system performance is evaluated using both static and dynamic phase aberration test conditions. Proc. SPIE Vol. 5894, p. 269-278, 2005.
Ground-Based Stellar Interferometry with Adaptive Optics C. Ting and M. K. Giles ABSTRACT A ground-based stellar interferometer appears to be a potentially useful research tool in studying stellar astrophysics and synthesizing a high resolution stellar image; however, its short-exposure performance is easily degraded by atmospheric turbulence. Even though adaptive optics has been recognized as a promising technology to improve image quality for a large aperture telescope, the question is often asked: "Is adaptive optics needed in a ground-based stellar interferometer?" In this paper, we develop the appropriate theory and provide simulation results to show why adaptive optics is needed in a ground-based optical interferometer. We also present a novel adaptive optics testbed including a tip-tilt error compensation system and a higher-order phase aberration compensation system to verify our theoretical simulation results. Proc. SPIE Vol. 5903, p. 32-41, 2005.
Adaptive Optics for the Magdalena Ridge Observatory C. Ting, M. Giles, and D. Voelz ABSTRACT Long-baseline optical interferometers have become useful tools for obtaining detailed stellar information and high-resolution images in the astronomy community. Several interferometric systems have been implemented successfully without adaptive optics; however, adaptive optical systems may be needed for a new generation of long-baseline interferometers with large telescopes such as those being developed for the Magdalena Ridge Observatory (MRO). This paper introduces the design trade-offs used to investigate the need for adaptive optics for a long-baseline optical interferometer operating in the turbulent atmosphere. Modeling techniques are combined with analytical equations to study the performance of a long-baseline optical interferometer with and without adaptive optics. Proc. SPIE 5237, 205-210, 2004.
Laboratory Testing of Components and Systems Used for Advanced Wavefront Control M. K. Giles, N. Wendelstein, A. Kohnle, and R. Weiss ABSTRACT As advanced wavefront control components and systems are developed, they must be tested. This paper describes the methodology and hardware used in the laboratory at FGAN-FOM, The Research Institute for Optronics and Pattern Recognition in Germany, to evaluate components and systems to be used for wavefront control. The test bed described is unique in two ways: (1) it uses a Hamamatsu parallel aligned liquid crystal phase modulator as a pupil plane phase screen to generate degraded input wavefronts for testing the wavefront control systems, and (2) it may be used to evaluate a variety of wavefront sensor, corrector, and control elements without changing the layout or realigning the optical components that comprise the basic test bed. For example, once the test bed is assembled and aligned, a desired wavefront sensor, with its matching telecentric pupil-imaging lens pair, is simply inserted at the end of the beam train, aligned with the test bed output beam, calibrated, and tested. Similarly, a desired wavefront corrector is inserted at the appropriate pupil plane, aligned, and tested. The paper also presents typical test results. Proc. SPIE Vol. 5553, pp. 301-308, 2004.
A Study of Variable Subaperture Size for Astronomical Adaptive Optics D. G. Voelz, M. K. Giles, J. Rha ABSTRACT We examine the utility of a wavefront sensor with a variable subaperture size for astronomical adaptive optics. A numerical analysis, based on wavefront variance and Strehl ratio expressions, was used to find the optimal subaperture size and wavefront sensor integration time for several case studies. The results show that a relatively smaller subaperture size can provide improved performance if the atmospheric coherence length r0 is also small and the source is relatively bright. Similarly, a larger subaperture size can improve performance if r0 is also large, the source is relatively dim, and the atmospheric temporal variation is relatively slow. These results suggest that a reconfigurable wavefront sensor could have utility for certain situations where conditions vary from nominal values. Proc. SPIE Vol. 5237, p.198-204, 2004.
Reconfigurable Shack-Hartmann Wavefront Sensor J. Rha, D. G. Voelz, and M. K. Giles ABSTRACT The conventional Shack-Hartmann wavefront sensor (SH-WFS) has a fixed subaperture area that is determined by consideration of several parameters such as the average atmospheric coherence diameter r(0) at the telescope site. Its SNR can be severely degraded due to low-light conditions caused by increasing turbulence, strong atmospheric scintillation, or simply viewing a faint object. Typically, the integration time of the sensor is increased to improve the SNR. Unfortunately, a decrease in bandwidth causes an increase in residual wavefront error that reduces image quality. We show that an increase in subaperture area produces a smaller residual wavefront error than an equivalent increase in integration time. Furthermore, we show that the ability to reconfigure the subaperture area, in combination with control bandwidth adjustment, provides superior performance over a system with fixed subaperture area when r(0) is different than the design point. We present a reconfigurable Shack-Hartmann wavefront sensor (RSH-WFS) with adjustable subaperture area implemented using a phase-modulated liquid crystal device (LCD). Experimental results demonstrate that the RSH-WFS increases system dynamic range by increasing the subaperture diameter whenever the Hartmann spot irradiance falls below the threshold of operation of the conventional SH-WFS. Opt. Eng. 43, 251-256, 2004.
Simulations of a Long-Baseline Interferometer with Adaptive Optics C. Ting, M. Giles, and D. Voelz ABSTRACT Simulation results of a long-baseline optical interferometer with adaptive optics are presented in this paper. Long-baseline optical interferometers have become useful tools for obtaining detailed stellar information and high-resolution images in the astronomy community. Several interferometric systems have been implemented successfully without adaptive optics; however, adaptive optical systems may be needed for a new generation of long-baseline interferometers with large telescopes such as those being developed for the Magdalena Ridge Observatory (MRO). A long-baseline optical interferometer in the turbulent atmosphere is modeled first, then an optical interferometer with an adaptive optics system (AOS) is modeled and the resulting fringe patterns for different input turbulence scales are interpreted. Finally, the performance of a long baseline optical interferometer with and without an AOS is carefully evaluated and recommendations are made for the implementation of adaptive optics in the 1.5-meter MRO telescopes. Proc. SPIE 5169, 250-254, 2003.
Adaptive Optics for the Magdalena Ridge Observatory M. K. Giles, C. Ting, and D. G. Voelz ABSTRACT Long-baseline optical interferometers have become useful tools for obtaining detailed stellar information and high-resolution images in the astronomy community. Several interferometric systems have been implemented successfully without adaptive optics; however, adaptive optical systems may be needed for a new generation of long-baseline interferometers with large telescopes such as those being developed for the Magdalena Ridge Observatory (MRO). This paper introduces the design trade-offs used to investigate the need for adaptive optics for a long-baseline optical interferometer operating in the turbulent atmosphere. Modeling techniques are combined with analytical equations to study the performance of a long-baseline optical interferometer with and without adaptive optics. Proc. SPIE 5237, 205-210, 2003.
