Experimental comparison of a Shack-Hartmann sensor and a phase-shifting interferometer for large-optics metrology applications.

We performed a direct side-by-side comparison of a Shack-Hartmann wave-front sensor and a phase-shifting interferometer for the purpose of characterizing large optics. An expansion telescope of our own design allowed us to measure the surface figure of a 400-mm-square mirror with both instruments simultaneously. The Shack-Hartmann sensor produced data that closely matched the interferometer data over spatial scales appropriate for the lenslet spacing, and much of the <20-nm rms systematic difference between the two measurements was due to diffraction artifacts that were present in the interferometer data but not in the Shack-Hartmann sensor data. The results suggest that Shack-Hartmann sensors could replace phase-shifting interferometers for many applications, with particular advantages for large-optic metrology.

Septal lesions facilitate the shift from conditioned escape to conditioned avoidance behavior in the rat.

Normal rats were given 1000 training trials in a discriminated lever-press avoidance task. Those animals which exhibited consistent escape behavior but minimal avoidance responding were subjected to either septal lesions or control operations. One week later they were retested in the avoidance apparatus for an additional 1000 trials. Rats with large septal lesions exhibited an immediate increase in avoidance performance relative to the control rats. This increase occurred without a concomitant increase in number of lever-press responses. The performance of 3 out of 4 rats with smaller more dorsal septal lesions was unaffected by the surgery.