Testing the APLC on the LAO ExAO testbed

We present testbed results of the Apodized Pupil Lyot Coronagraph (APLC) at the Laboratory for Adaptive Optics (LAO). This coronagraph is being built for the Gemini Planet Imager (GPI). The apodizer component is manufactured with a halftone technique using black chrome microdots on glass. Testing this APLC (like any other coronagraph) requires extremely good wavefront correction, which is obtained to the 1nm RMS level on the Extreme Adaptive Optics (ExAO) visible testbed of the Laboratory Adaptive optics (LAO) at the University of Santa Cruz. With this testbed, we investigated the performance of the APLC coronagraph and more particularly the effect of the apodizer profile accuracy on the contrast. We obtained the first image of a dark zone in a coronagraphic image with a MEMS deformable mirror. Finally, we compare the resulting contrast to predictions made with a wavefront propagation model of the testbed to understand the effects of phase and amplitude errors on the final contrast.

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