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.
In this paper, a local optimization algorithm (Levenberg-Marquardt algorithm) is employed for broadband EUV multilayer design. A merit function is optimized in the Levenberg-Marquardt algorithm, for achieving maximum reflectivity of the designed broadband EUV multilayer mirrors. Using this algorithm, the reflectivity of broadband EUV multilayer mirrors with different broadband for various central photon energy are designed and compared. Under the condition of normal incidence, the maximum average reflectivity of designed broadband EUV multilayer mirrors with 20 eV bandwidth for 40 eV, 60 eV and 80 eV central photon energy are 6%, 16% and 21% respectively, while the ones with 10 eV, 20 eV and 30 eV bandwidth for 80 eV central photon energy are 29%, 21% and 15% respectively. In addition, the effect of incident angle on the reflectivity of broadband EUV multilayer mirrors is also studied. It is found that the maximum average reflectivity of designed broadband EUV multilayer mirror with 20 eV bandwidth for 80 eV central photon energy increases from 21% to 53%, when the incident angle of light increases from 0° to 60°. We believe this research is important because it provides a guide for the design of broadband EUV multilayer mirrors with high reflectivity.
In this paper, the comparative study of sensitivity of NGWSPR biosensor with Au, Ag, Cu and Al is presented. To achieve high sensitivity, the thickness of each layer in the proposed biosensor is optimized using genetic algorithm (GA). A constraint condition of reflectivity at resonance angle is used in the merit function (MF) of GA to realize large depth of dip. Using this method, NGWSPR biosensors with Au, Ag, Cu and Al are designed and analyzed. The sensitivity of designed Ag based NGWSPR biosensor is up to 289 °/RIU when using TiO2 as the dielectric, which is 31.83%, 24.91% or 61.94% higher than the sensitivity of designed Au, Cu or Al based one. We believe our work is important because it compares the largest sensitivities of NGWSPR biosensors with different metals, and be helpful for highly sensitive biosensors development.
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