Nonlinear self-focusing by intense UV laser in fused silica

The effects of the environmental condition and the beam quality of the third harmonic UV laser with a pulse width of about 1 ns and a wavelength of 351 nm on the self-focusing intensity and self-focusing distance in fused silica were analyzed. The threshold of the nonlinear self-focusing of the UV laser was studied. The results show that, for the given beam quality of UV laser, the value of B integral remains almost the same, which can be defined as the threshold of the nonlinear self-focusing effect. The worse the beam quality is, the lower the threshold is. Furthermore, the dusts in the air can induce self-focusing in fused silica even for the input UV laser with uniform intensity and phase distributions. Moreover, when the dust particle is larger, the self-focusing effect is more obviou