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Experimental setup for plasma density measurement using the Mach-Zehnder interferometer and optical guiding through the capillary. Top image of Fig. 1 represents the gas feed-lines for the tapered capillary, and the bottom image on CCD is a small part of a long interferogram that was formed when the laser beam passed through the capillary plasma transversely.
On-axis and spatially averaged plasma densities measured as a function of the longitudinal position for different pressures. The density gradient was demonstrated in the 15-mm-long square-bore capillary with 400 μm × 400 μm cross-section.
(a) Time-resolved on-axis plasma densities and (b) transverse plasma density profiles at t = 140 ns. In the figures, z is the longitudinal distance from the capillary entrance. In Fig. 3(a) , the minimum and maximum density values for ten repeated measurements are indicated as an error bar. Hence, rms (root mean square) error bars, which are more physically meaningful, will be significantly smaller.
(a) Energy transmission of laser pulses as a function of time delay when the laser beams are focused to a spot size of 48 μm at the capillary entrance. The solid line is the discharge current, and the hollow triangles represent the energy transmission with 20 ns intervals. (b) Laser beam images at the focal point and at the exit plane of the capillary for various time delays.
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