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A fast modal wave-front sensor

Erez N. Ribak and Steven M. Ebstein

Open Access Open Access

Abstract

We describe an instantaneous modal wave-front sensor. The sensor uses a Shack-Hartmann lenslet array to encode the wave-front distortion. A novel parallel electro-optic processor continuously converts the spot pattern to wave-front modes, e.g. Zernike polynomials, without a separate reconstructor. Using readily available components, the sensor can achieve MHz bandwidths for twenty modes. The bandwidth, sensitivity, and number of bits can vary for each mode to match the sensor to the disturbance in an optimal fashion. The proposed sensor has immediate application to beam control and turbulence sensing applications that require wide bandwidths. The measured wave-front modes can also be those of an adaptive optics system, directly providing control signals for the actuators of a deformable mirror. A similar electronic reconstructor mode is also described.

©2001 Optical Society of America

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Figures (4)
Figure 1.
Figure 1. Modal wave-front sensor: (a) schematic model, (b) optical and (c) electronic realizations. HS Hartmann Shack lenslet array; C/IC coherent to incoherent converter; A amplifier; MUX multiplexer; M mask array; X, MULT multiplier; ∑, SUM integrator; II image intensifier; C collimator; L lens array; D detector array; A/D analog to digital converter.

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Figure 2.
Figure 2. The first twelve Zernike masks. Light from a copy of the Hartmann pattern with thirty spots impinges on each mask and the signal integrated by a single mode detector.

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Figure 3.
Figure 3. Two Hartmann patterns from a laser beam, differing mainly in focus and tilt.

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Figure 4.
Figure 4. Integrating the signals from the central element (0,0) at the top left. Each actuator signal amounts to integration from the center to its position along a few shorter paths.

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Tables (1)

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Table 1: Zernike Coefficients for the masks shown in Figure 2 and the two patterns shown in Figure 3.

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