Mach-Zehnder interferometry at framing rates of 10.5--21 GHz

A simple beam splitter arrangement is used to divide a single ultrashort optical pulse into four beams of accurately known jitter-free delay. The 50-ps ruby laser beams are used in a Mach-Zehnder interferometer to produce four interferograms in one shot of the CO2-laser-irradiated plasma at an interframe delay of 95 ps. Fringe straightness of <1/10 wave error is attained in all four frames by overlapping reference and scene beams precisely on the film while relaxing the constraint of the high spatial coherence necessary in shearing and folding shear interferometry. Such high fringe quality is required to record properly the observed fractional fringe shifts in a plasma of electron density up to n/sub e/ = 5 x 1018 cm-3. The four-frame interferogram, recorded on Polaroid-type 667 film, is available immediately after the shot is taken. Neither a streak camera for recording timing sequences nor wavelength filters for rejection of plasma light was required. Simple rearrangement of optical components allows framing rates of 10.5 or 21.0 GHz