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L.E. Marchese, D. Brousseau, E.F. Borra, J. Faubert; Employing Two Deformable Mirrors Significantly Improves Adaptive Optics Wavefront Sensors . Invest. Ophthalmol. Vis. Sci. 2006;47(13):1194.
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© ARVO (1962-2015); The Authors (2016-present)
The purpose of this research project was to develop an adaptive optics wavefront sensor incorporating two deformable mirrors. Such a system may be useful for achieving larger and more accurate wavefront corrections.
A simple design of a two–mirror system was simulated in Code V. First, a model eye was designed that consisted of a point source emanating from the retina and passing through a phase plate (representing the ocular aberrations). Next, two deformable mirrors were modeled as reflective Zernike polynomial surfaces and were placed at conjugate planes. Finally, the reflected light from the second mirror was passed through a100 mm focal length achromat lens and imaged at its focal plane. The wavefront error of the system was measured at the entrance pupil. A constrained optimization was performed to minimize each of the system’s 15 Zernike coefficients. The iteration variables were the 15 Zernike sag coefficients of the mirrors and the constraint was the mirror maximum stroke. In the case of the single–mirror configuration, the first mirror was left untouched as a plane, and in the two–mirror case, the mirror sags were optimized simultaneously. Comparisons were made of the residual wavefront error and point spread functions for corrections between the single and dual mirror configurations. Three simulations were run. In each case the model eye had an entrance pupil of 6 mm. The peak–to–peak wavefront errors of each eye were (respectively) 12.37 µm, 10.22 µm and 14.76 µm. The RMS wavefront errors were 3.29 µm, 2.66 µm and 3.33 µm. For the first two mirror designs, the stroke of each deformable mirror was limited to ±2 µm whereas in the third case the stroke was limited to ±5 µm.
The following are the wavefront errors after optimization of the mirror surface shapes: peak–to–peak errors were 3.25 µm, 1.60 µm and 3.40 µm with the single mirror and 1.44 µm, 0.07 µm and 0.67 µm with the two mirrors; RMS errors were 0.73 µm, 0.28 µm and 0.20 µm with the single mirror and 0.27 µm, 0.01 µm and 0.10 µm with the two mirrors. In addition, the Strehl ratios for each case were 0.00, 0.20 and 0.01 for the single–mirror configuration and 0.33, 0.45 and 0.41 for the two–mirror configuration.
The feasibility of a two–deformable–mirror adaptive optics system has been demonstrated. Simulations have shown that for eyes with aberrations too large for a single mirror to correct, a second mirror may be employed. In such a two–mirror configuration, the total stroke of the adaptive optics system is increased, resulting in a better ocular correction.
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