ISR CDS Lectures CDS Lecture Series

Friday, September 20, 2001, 2:00 p.m.

Eric Justh
Institute for Systems Research, University of Maryland
Intelligent Optics Laboratory, Army Research Lab

High-resolution optical wave front sensing and control

A coherent optical beam passing through the atmosphere is subject to wave-front distortion: thermal gradients in the air produce index-of-refraction variations, and hence optical path-length variations, over the cross-section of the beam. Adaptive optics is the discipline concerned with real-timecompensation of such wave-front distortion, and has had major impact, e.g., inastronomical imaging. In conventional adaptive optic systems, wave-front correction is achieved using a deformable mirror (with at most several hundred degrees of freedom) to cancel the wave-front distortion. A wave-front sensor capable of measuring the residual distortion is also required, and the challenge is that optical wave front, or phase, can be measured only indirectly. In conventional systems, spatial derivatives of the wave front are measured, and numerical techniques are used to, in effect, reconstruct the wave front from the spatial derivative measurements.

Recent advances in high-resolution spatial light modulators (SLMs) based onliquid-crystal and microelectromechanical (MEMS) devices have opened up the possibility for high-resolution wave-front sensing and control (with 10^4 degrees of freedom for wave-front correction). However, in addition to the devices, there is also a need for control laws which scale appropriately for the high-resolution regime. In recent work arising from a collaboration between the ISR and the Army Research Lab, we have analyzed and demonstrated a control scheme appropriate for high-resolution adaptive optics. Inexpensive, high-speed, high-resolution wave-front control has potential applications in imaging (both astronomical and terrestrial), point-to-point laser communications, laser radar, phase-contrast microscopy, and directed-energy applications.

This talk primarily describes the modeling, analysis, and experimental work on the high-resolution wave front sensing and control system developed jointly with Professor P.S. Krishnaprasad at the University of Maryland and Dr. Mikhail Vorontsov and his group at the Intelligent Optics Laboratory at the Army Research Laboratory in Adelphi, Maryland.

[1] E.W. Justh, P.S. Krishnaprasad, and M.A. Vorontsov, "Nonlinear Analysis of a High-Resolution Optical Wavefront Control System," Proc. 39th IEEE Conference on Decision and Control, 3301-3306, IEEE, New York, 2000.

[2] E.W. Justh and P.S. Krishnaprasad, "Analysis of a High-Resolution Optical Wavefront Control System,"
Proc. Conf. on Information Sciences and Systems, Vol. 2, pp. 718-723, 2001.

[3] M.A. Vorontsov, E.W. Justh, and L.A. Beresnev, "Adaptive Optics with Advanced Phase Contrast Techniques: Part I. High-Resolution Wavefront Sensing," Journal of the Optical Society of America A, Vol. 18, No. 6, pp.1289-1299, 2001.

[4] E.W. Justh, M.A. Vorontsov, G.W. Carhart, L.A. Beresnev, and P.S. Krishnaprasad, "Adaptive Optics with Advanced Phase-Contrast Techniques: Part II. High-Resolution Wavefront Control,"
Journal of the Optical Society of America A, Vol. 18, No. 6, pp. 1300-1311, 2001.

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