Recent advancements in ultraintcnse,short pulse lasers have allowed for the exploration of many novel regimes in the field of laser-plasma interactions.Energetic charged particles generated by laser-plasma interactions can be used in many applications including the imtiation of tabletop particle accelerators as well as fusion by fast ignition.The generation of energetic particles by the interaction of an ultraintense laser pulse with a plasma has been demonstrated in theoretical[1-4] and experimental studies.A fast ignitor concept[5] was proposed as the approach to efficiently ignite the high density fusion fuel plasmas with an ultraintense short pulse laser.In the fast ignitor scheme,the intense laser pulse propagates through a colonial plasma up to several times the critical density and delivers energy to high energy electrons.These highly energetic particles then transport the energy through the overdense plasma to the center of the compressed core and ignite the fuel there.It is known that interactions of ultraintense laser pulses with overdense plasmas lead to the generation of a magnetic field the so-called Weibel instability[5-9].The Weibel-type instability breaks up the fast electron current into filaments.Particle-in-Cell(PIC)simulations have shown the break up of fast electron beams into filaments guided by magnetic fields[6-7].In this paper,we present Particle-in-Cell (PIC) simulation of the interaction of ultraintense laser pulses with plasmas.Intense self-generated magnetic fields is produced by the mechanism of Weibel instabiliti in underdense plasmas.