Study of self-trapped optical beams by high-speed holography

Output of a 10-MW
Q
-switched Nd
³⁺
glass laser was focused into several kinds of liquid media, and the change in the refractive indices
\deltan
due to the focused laser beam was observed by means of double exposure holography using a
Q
-switched ruby laser as the light source. It has been shown that a filament of several 10 μ in diameter and several mm in length is formed around the focal point. The filament remains almost unchanged more than several μs. The sign of
\deltan
after the passage of the laser beam is negative. The temperature change at the filament has been estimated to be about 0.2°C, assuming
\deltan
to be caused entirely by thermal effect of the beam. The absorption of the laser beam that causes this temperature change has been found to be linear in the flux density, the absorption coefficient being
2 \times 10^{-3}
cm
^-1
in CS
2
. The growth of spherical and plane pressure waves has also been observed.