The principles and concepts of a wave-front analyzer based on spot edge scanning techniques and rising and falling illuminance slope comparisons are reviewed. An analyzer implementing these techniques and designed to be used with an adaptive optics element for the real time correction of low order aberrations is described. An evaluation of the tilt output channels of the analyzer shows a linear operating range exceeding ±500 μrad, frequency response exceeding 250 Hz, and a noise equivalent tilt angle of 4 μrad. For the focus and astigmatism channels, the analyzer output is linear over an ∼2.5–3-μm range of aberration input for a diffraction-limited (DL) spot. The instrument gain falls from ∼8.5 V/μm for a 1 × DL spot to ∼4 V/μm for a 6 × DL spot. The noise equivalent aberration increases from 0.025 μm for a 1 × DL spot to ∼0.05 μm for a 6 × DL spot.
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