Particle-in-cell (PIC) simulations show that an
anisotropic electron velocity distribution is demonstrated
by ultraintense laser pulses in underdense plasmas. Recently,
it is reported that the anisotropy has been experimentally
demonstrated in laser-produced plasmas. It is also pointed
out that gigagauss magnetic fields are generated by ultraintense
laser pulses. We have already published that the Weibel-type
electromagnetic instabilities can be theoretically excited
by electrons in a velocity distribution with anisotropic
temperature. If these electromagnetic waves are excited,
the target may have a possibility not only to give rise
to a new type of energy loss mechanism but also to influence
the implosion characteristics. In this work, we present
PIC simulation of the interaction of ultraintense laser
pulses with plasmas. Intense self-generated magnetic fields
is produced by the mechanism of Weibel instability in underdense
plasmas.