A micro-second under-water wire explosion is investigated by Cranz-Schardin high speed photographic method using two nitrogen lasers as light sources.
Two low pressure (20-80 torr) compact nitrogen lasers are designed, constructed and transversely excited using Blumlein transmission line made of mylar (0.4mm thickness) and copper foil (35 μm thickness).
The laser radiation has a wavelength of 3371 Å with 1.4 Å line-width. This is measured by using a 1m Czerny-Turner spectrograph. The beam divergence is calculated to be 5.4 mrad and the experimental measurement gives 5.8 mrad in horizontal direction and 7.1 mrad in vertical direction. Brightness of 5×$10^9$ watt/㎠ str. is estimated. The high degree of spatial coherence is confirmed from Young's interferometer using two 30μm slits with varying separation.
Copper wires, 0.1mm in diameter and 10mm long, are exploded in water by short-circuiting a 2μF capacitor charged up to 5 kV.
From the high speed photographies with delay time, $3.5 μ\sec$ and $10\mu\sec$, the wire under water is found to melt immediately $t\simeq0(＜40n\sec)$ and then a striation begins at a spot at $3.5\mu\sec$. At $t=10\mu\sec$, striations are observed at various positions along the exploding copper wire.