Photoelectronic mapping of the spin–orbit interaction of intense light fields

Abstract

The interaction between a quantum particle’s spin angular momentum1 and its orbital angular momentum2 is ubiquitous in nature. In optics, the spin–orbit optical phenomenon is closely related with the light–matter interaction3 and has been of great interest4,5. With the development of laser technology6, the high-power and ultrafast light sources now serve as a crucial tool in revealing the behaviour of matter under extreme conditions. A comprehensive knowledge of the spin–orbit interaction for intense light is of utmost importance. Here, we report the in situ modulation and visualization of the optical orbital-to-spin conversion in the strong-field regime. We show that, through manipulating the morphology of femtosecond cylindrical vector vortex pulses7 by a slit, the photon’s orbital angular momentum can be controllably transformed into spin after focusing. By employing a strong-field ionization experiment, the orbital-to-spin conversion can be imaged and measured through the photoelectron momentum distributions. Such detection and consequent control of the spin–orbit dynamics of intense laser fields has implications for controlling photoelectron holography and coherent extreme-ultraviolet radiation8. Sculpting and focusing femtosecond cylindrical vector vortex pulses by a slit allows the controllable transformation of the photon’s orbital angular momentum into spin angular momentum, which can be characterized in situ by a strong-field ionization experiment.