Focal switch of broadband laser in a dispersion dual-focus system

Focal switch effect of broadband laser in a dispersion dual-focus system with large Fresnel number is reported in this paper. Influences of the bandwidth on the intensity distributions and focal switch are illustrated by numerical examples. The results indicate that the bandwidth brings on the variations of two maximum intensities on the axis and thus results in the generation of focal switch. Fresnel number and the distance between two lenses also have influence on the focal switch. The bandwidth needed for the generation of the focal switch decreases when the Fresnel number and the distance between the two lenses increase. Narrow bandwidth can induce the focal switch in the system with large Fresnel number but the bandwidth needed for the generation of the focal switch increases rapidly when the Fresnel number decreases.