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The present work explores the study of terahertz (THz) wave generation by the cross-focusing of two Gaussian laser beams in a bulk medium containing graphite nanoparticles (NPs). This system acts as a nonlinear medium behaving like plasma. The ripple is applied on the density of NPs to increase the conversion efficiency. Using the perturbative technique, a wave equation is derived which describes the nonlinear interaction of the laser beam with NPs. The nonlinear current at THz frequency arises due to the ponderomotive force exerted on the electrons of graphite NPs by the incident laser beams in the presence of density ripple. This nonlinearity depends on the intensities of both the beams. Hence the focusing of one beam affects the focusing of the other, resulting in the cross-focusing of the beams. Numerical results show that the normalized amplitude of the generated THz wave increases by 3.5 times with the consideration of the phenomenon of cross-focusing. The results show the enhancement in the efficiency of generated THz wave on application of density ripple, due to the fulfillment of the phase matching condition.

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