Excimer laser

The invention discloses an excimer laser, comprising a seed cavity, an amplifying cavity and a light path transmission structure. The seed cavity is used for outputting seed laser; the amplifying cavity is used for amplifying the energy of the seed laser; the light path transmission structure is used for guiding the transmission of the laser, wherein the light path transmission structure comprises a first triangular prism, a second triangular prism and a third triangular prism. By adopting triangular prisms with special angles and special placing manners to the triangular prisms, the excimer laser of the invention could achieve mutual compensation of phase difference of a P light and an S light so that the light path transmission structure will not generate additional phase difference to achieve the goal of enabling the polarization state of the laser which is finally output and the polarization state of the seed laser output from a discharging cavity to be consistent and holding the stability of the polarization states of the laser.