In this paper, based on a full vector-diffraction theory, we present a systematic investigation of the characterization of tight-focused vector fields formed by an off-axis parabolic mirror (OAP), and discuss the effects of offset of an OAP, polarization of light and parabola f-number on the focused field properties by an OAP used with a perfectly aligned beam. Furthermore, we demonstrate a configuration optimization process of an OAP, and obtain an optimum OAP configuration scaling rule which makes it possible to achieve the maximum peak intensity. In addition, we explore the electromagnetic field behaviour in the focal plane at four characteristic times of an optical cycle we explore the electromagnetic field behaviour in the focal plane at four characteristic times of an optical cycle and the dependence of the direction and the amplitude of the focused electromagnetic field on the incident polarization, the offset, and the parabola f-number. we also carry out an assessment analysis of the critical misalignment angle corresponding to a 10% drop of the maximum focused peak intensity. Understanding these effects and scaling laws is of great significance to enhance the focusing performance of OAP in the optimal configuration, especially for the structural design and selection of OAP in ultrashort and ultraintense laser-matter interaction experiments.
A tunable dual-band infrared polarization filter has been proposed and investigated in this paper. Based on the perfect absorption characteristic of the metal-dielectric-metal sandwich structure, the reflection spectrum shows filter performance. This filter consists of three layers. The top layer is a compound metal nano-structure array composing of an asymmetrical cross resonator and a rectangle strip. The middle and bottom layer are dielectric spacer and metal film, respectively. The calculated results show that the filter property is closely related to the polarization of incident light. When the light polarization parallels to the long direction of the rectangle strip, two resonant wavelengths (1310nm and 2000nm) are filtered, and in contrast only one resonant wavelength (1516nm) is filtered when light polarization vertical to it. Moreover, we found that the resonant wavelength is strongly depended on the length of the rectangle strip which caused the resonant effect. Therefore, the filter wavelength can be tuned freely for different light polarization by adjusting the length of the corresponding rectangle strip. We can change one or two filter wavelengths at a time or change the three filter wavelengths at the same time. In addition, the calculated results show all the intensities at the filter wavelengths are closed to zero, which implies the filter can exhibit good filtering performance.
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