Highly efficient plasma-based circular polarizer for high-intensity X-ray lasers
Y.J.Dong¹, P. Chen¹, K. Jiang¹, H. Peng¹, R. Li¹, and T.W.Huang^1*
1Center for Intense Laser Application Technology, and College of Engineering Physics, Shenzhen Technology University, Shenzhen 518118, China
Email: huangtaiwu@sztu.edu.cn

Manipulating the polarization state of X-ray laser pulses is an important yet challenging issue. Existing X-ray polarization converters (e.g., elliptical polarization undulators) are only suitable for low-power scenarios and are prone to damage under high power. To address the vulnerability of traditional devices for high-power X-ray polarization control, this study proposes a highly efficient polarization conversion scheme based on total reflection at solid-density plasma interfaces. It is well known that when light travels from a denser optical medium to a rarer one and the incident angle exceeds the critical angle, the laser undergoes total reflection and a phase difference between the p-polarized component and the s-polarized component is introduced in the reflected wave. Since the refractive index of plasma is less than unity when the plasma density is less than the critical density of X-ray wavelength laser, the solid-density plasma in principle can be used as a total-reflection interface to achieve effective linear-to-circular polarization conversion for high-power X-ray laser. Our particle-in-cell (PIC) simulations demonstrate that in the interaction between high-power lasers and plasma interfaces, while the excitation of surface plasmon polaritons induces plasma density perturbations and leads to a slight decrease in reflection efficiency, the single-shot reflection efficiency still remains above 95% for a wide range of laser parameters. For a solid plasma with a density of 7.8×10²⁹ m^-3, it is predicted that X-ray laser with wavelength less than 37.5nm can achieve linear-to-circular polarization conversion if considering multiple total reflections. In addition, the polarization states can be continuously adjustable by tuning the incident angle and plasma parameters. This scheme overcomes the damage limitations of conventional devices, offering a novel approach for high-power X-ray polarization control with both high damage threshold and high efficiency.


 

X-ray lasers;,Plasma,total reflection,surface wave,polarization conversion