Development of a laser wavefront sensor for measurement of discharges in air

A laser wavefront sensor of the Shack-Hartmann type capable of simultaneous measurement at two wavelengths was constructed. The sensor uses a single optical path, and is suited for applications such as high-voltage discharges in air, in which large insulation distances are necessary. The sensor was used to detect optical path differences due to an impulse discharge in air across a needle-plane electrode gap of gap length 17 mm. Optical path differences were measured at laser wavelengths of 532 and 1064 nm at 1.6 mus after insulation breakdown across the gap. From the difference in optical path differences at the two wavelengths, a line-integrated electron density distribution in the direction perpendicular to the gap was obtained near the high-voltage electrode. The distribution had a peak value of 1.4 x 10(20) m(-2) and a full width at half maximum of 4.4 mm. Because of the coverage of a large observation area including the entire gap, the spatial resolution was 1.4 mm, which was inadequate to obtain the precise form of the electron density distribution. However, the results show the possibility of applying laser wavefront sensing to electron density measurement. (C) 2004 Wiley Periodicals, Inc.