Design of extreme ultraviolet quarter wave plate based on linearly chirped multilayer mirror

Abstract

The quarter wave plate applied to the extreme ultraviolet (EUV) region can realize the conversion of linear polarization and circular polarization EUV light source, so it has a wide range of applications such as magnetic microscopy techniques based on circularly polarized light. In this paper, a lineally chirped Mo/Si multilayer mirror is used to design a EUV quarter-wave plate. With the increasing thickness variation value of linearly chirped multilayer, the reflective phase delay between s- and p-polarized light increases at first and then realizes its maximum value. In this case, a quarter wave plate that can realize 90° phase delay can be designed by optimizing the structure parameters of a linearly chirped multilayer mirror. A linearly chirped Mo/Si multilayer which contains 13 pairs of bilayers with 14.7 nm central thickness and 1.94 nm thickness variation can achieve a reflective phase retardation of 89.95° at 90 eV under 30° grazing incidence. At the same time, the reflectivity of s- and p-polarized light are 47.65% and 10.09% respectively. The development of an EUV quarter wave plate based on a linearly chirped multilayer mirror could promote the research on the production and application of circularly polarized EUV light sources.