USE OF A DOUBLE-WOLLASTON PRISM LASER DIFFERENTIAL INTERFEROMETER IN A PLASMA-FOCUS

A double-Wollaston prism laser differential interferometer (LDI) has b een developed to observe, for the first time, the evolution of the imp loding current sheath (CS) and the high temperature and high density p lasma pinch in the plasma focus. The light source is a e-switched and frequency-doubled YAG laser operated in a single-pulse mode: lambda = 532 nm, the pulse width (FWHM) about 10 nm (also the resolution time o f the LDI). The LDI measures density gradients and has a Line sensitiv ity of about n(e)' = (2.58 +/- 0.46) x 10(25) m(-4) for a typical shea th thickness of 1.6 mm and a minimum distinguishable fringe shift of 5 %, and a spatial resolution of 1.26 mm. The density gradient and equiv alent density of the CS are measured to be n(e)' approximate to (2.58 +/- 0.46) x 10(26) m(-4) and n(e) approximate to (3.25 +/- 0.59) x 10( 23) m(-3), respectively. More importantly in this article, the double- Wollaston prism LDI, with a simple optical arrangement, gives direct p hysical pictures of the high density gradient plasma configuration and Structure which are of interest in studying the status of plasma moti on. (C) 1997 American Institute of Physics.