Departament de Física, Universitat Autònoma de Barcelona, E-08193 Bellaterra, Spain.
Center of Advanced European Studies and Research, 53175 Bonn, Germany.
Sci Rep. 2017 Mar 10;7:43888. doi: 10.1038/srep43888.
We investigate theoretically the generation of extreme-ultraviolet (EUV) beams carrying fractional orbital angular momentum. To this end, we drive high-order harmonic generation with infrared conical refraction (CR) beams. We show that the high-order harmonic beams emitted in the EUV/soft x-ray regime preserve the characteristic signatures of the driving beam, namely ringlike transverse intensity profile and CR-like polarization distribution. As a result, through orbital and spin angular momentum conservation, harmonic beams are emitted with fractional orbital angular momentum, and they can be synthesized into structured attosecond helical beams -or "structured attosecond light springs"- with rotating linear polarization along the azimuth. Our proposal overcomes the state of the art limitations for the generation of light beams far from the visible domain carrying non-integer orbital angular momentum and could be applied in fields such as diffraction imaging, EUV lithography, particle trapping, and super-resolution imaging.
我们从理论上研究了产生携带分数轨道角动量的极紫外（EUV）光束的方法。为此，我们利用红外锥形折射（CR）光束驱动高阶谐波产生。我们表明，在 EUV/软 X 射线区域发射的高阶谐波光束保留了驱动光束的特征，即环状横向强度分布和 CR 样偏振分布。因此，通过轨道角动量和自旋角动量守恒，谐波光束以分数轨道角动量发射，并且可以通过旋转的线偏振沿着方位角合成具有旋转线性偏振的结构化阿秒螺旋光束——或“结构化阿秒光弹簧”。我们的方案克服了在远离可见光域产生携带非整数轨道角动量的光束的现有技术限制，可应用于衍射成像、EUV 光刻、粒子俘获和超分辨率成像等领域。
