PROTOTYPE IMAGING 2ND-HARMONIC INTERFEROMETER

We have built a prototype imaging second harmonic interferometer, whic h is intended to test critical elements of a design for a tangential a rray interferometer on C-Mod(6). The prototype uses a pulsed, 35 mJ, 1 0 Hz multimode, Nd:YAG laser, LiB3O5 doublers, a fan beam created by a cylindrical lens, four retroreflector elements, and a CCD camera as a detector. The prototype also uses a polarization scheme in which the interference information is eventually carried by two second harmonic beams with crossed polarization. These are vector summed and differenc ed, and separated, by a Wollaston prism, to give two spots on the CCD. There is a pair of these spots for each retroreflector used. The phas e information is directly available as the ratio of the difference to sum the intensities of the two spots. We have tested a single channel configuration of this prototype, varying the phase by changing the pre ssure in an air cell, and we have obtained a 5:1 light to dark ratio, and a clear sinusoidal variation of the ratio as a function of pressur e change. (C) 1997 American Institute of Physics.