Abstract
With the rapid development of femtosecond lasers, the generation and application of optical vortices have been extended to the regime of intense-light-matter interaction. The characterization of the orbital angular momentum (OAM) of intense vortex pulses is very critical. Here, we propose and demonstrate a novel photoelectron-based scheme that can in situ distinguish the OAM of the focused intense femtosecond optical vortices without the modification of light helical phase. We employ two-color co-rotating intense circular fields in the strong-field photoionization experiment, in which one color light field is a plane wave serving as the probing pulses and the other one is the vortex pulses whose OAM needs to be characterized. We show that by controlling the spatial profile of the probing pulses, the OAM of the vortex pulses can be clearly identified by measuring the corresponding photoelectron momentum distributions or angle-resolved yields. This work provides a novel in situ detection scenario for the light pulse vorticity and has implications for the studies of ultrafast and intense complex light fields with optical OAM.
Highlights
Optical vortex beams carry the well-known optical orbital angular momentum (OAM) of lћ per photon[1], where l is usually an integer number and denotes the topological charge of the field
Since the dynamic signature of vortex beams is determined by the OAM mode[9], the OAM mode measurement is one of the crucial tasks which is prior to the applications of vortex beams
We use the 800nm light field as the probing pulses and the 400-nm light field whose OAM needs to be characterized as unknown pulses
Summary
Optical vortex beams carry the well-known optical orbital angular momentum (OAM) of lћ per photon[1], where l is usually an integer number and denotes the topological charge of the field. One main approach is to utilize the interferometric techniques, in which the number of the stripes in the specific interferograms are related to the topological charges[10,11,12,13]. Another traditional choice is to use diffraction
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