Gariepy Genevieve, Leach Jonathan, Kim Kyung Taec, Hammond T J, Frumker E, Boyd Robert W, Corkum P B
Joint Attosecond Science Laboratory, University of Ottawa and National Research Council, Ottawa K1A 0R6, Canada.
Department of Physics, University of Ottawa, Ottawa K1N 6N5, Canada and IPaQS, SUPA, Heriot-Watt, Edinburgh EH14 4AS, United Kingdom.
Phys Rev Lett. 2014 Oct 10;113(15):153901. doi: 10.1103/PhysRevLett.113.153901. Epub 2014 Oct 7.
A beam with an angular-dependant phase Φ = ℓϕ about the beam axis carries an orbital angular momentum of ℓℏ per photon. Such beams are exploited to provide superresolution in microscopy. Creating extreme ultraviolet or soft-x-ray beams with controllable orbital angular momentum is a critical step towards extending superresolution to much higher spatial resolution. We show that orbital angular momentum is conserved during high-harmonic generation. Experimentally, we use a fundamental beam with |ℓ| = 1 and interferometrically determine that the harmonics each have orbital angular momentum equal to their harmonic number. Theoretically, we show how any small value of orbital angular momentum can be coupled to any harmonic in a controlled manner. Our results open a route to microscopy on the molecular, or even submolecular, scale.
一束围绕光束轴具有与角度相关的相位Φ = ℓϕ的光束，每个光子携带ℓℏ的轨道角动量。此类光束被用于在显微镜中提供超分辨率。产生具有可控轨道角动量的极紫外或软X射线光束是将超分辨率扩展到更高空间分辨率的关键一步。我们表明，在高次谐波产生过程中轨道角动量是守恒的。在实验中，我们使用|ℓ| = 1的基波，并通过干涉测量确定各谐波的轨道角动量等于其谐波次数。在理论上，我们展示了如何以可控方式将任意小的轨道角动量值耦合到任意谐波。我们的结果为分子甚至亚分子尺度的显微镜研究开辟了一条途径。
