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

The interaction between a quantum particle’s spin angular momentum 1 and its orbital angular momentum 2 is ubiquitous in nature. In optics, the spin–orbit optical phenomenon is closely related with the light–matter interaction 3 and has been of great interest 4 , 5 . With the development of laser technology 6 , 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 pulses 7 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 radiation 8 .