In order to research the effects of frequency bandwidth on the propagation and applications of broadband laser, the propagation formula of broadband laser with rectangular spectrum passing through a bifocal dispersion lens system was derived by using diffraction integral. Bandwidth-induced focal switch in broadband laser with rectangular spectrum is studied by numerical calculation. The effects of bandwidth on the intensity distribution and focal switch were analyzed. The results show that bandwidth is an important factor affecting intensity distribution and focal switch. Primary maximum inten...