Adaptive wavefront correction uses all-optical feedback

Researchers at the Mechanical Engineering Laboratory (Tsukuba, Japan), the University of Auckland (Auckland, New Zealand), and Industrial Research Limited (Lower Hutt, New Zealand) have built an adaptive wavefront-correction system based on an all-optical feedback interferometer.

Researchers at the Mechanical Engineering Laboratory (Tsukuba, Japan), the University of Auckland (Auckland, New Zealand), and Industrial Research Limited (Lower Hutt, New Zealand) have built an adaptive wavefront-correction system based on an all-optical feedback interferometer. The two-dimensional output fringe pattern from a Mach-Zehnder interferometer with large radial shear is optically fed back to an optically addressed nonpixelized phase-only liquid-crystal spatial light modulator (SLM)--an interferometric setup that does not require a separate aberration-free reference wave.

For testing purposes, the researchers sent a plane wavefront from a 19.5-mW HeNe laser through a plate with several waves of aberration to produce a distorted input wavefront. To increase feedback-loop gain to the point where the system worked, the researchers adjusted the SLM for a response time of 60 ms and a resolution of 60 line pairs/mm. Without feedback, the wavefront was highly distorted--a focused spot exhibited a Strehl ratio of 0.22. When the loop was closed, the Strehl ratio reached 0.92. Contact Tomohiro Shirai at shirai@mel.go.jp.

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