Figure 3: OAM spectrum of the fundamental beam (red bars), the 17th harmonic (blue bars) and the 23rd harmonic (pink bars).
From: Extreme Ultraviolet Fractional Orbital Angular Momentum Beams from High Harmonic Generation
The two components of the fundamental CR beam are clearly distinguished: the B0 beam (
, 
), and the B1 beam (
, 
). Thus, the fundamental beam exhibits fractional-OAM 
. The high-order harmonics present analogously two OAM contributions with counter-rotating polarization, corresponding to the R and L absorption channels. Angular momentum conservation conveys the generation of fractional-OAM harmonics: 
, and 
. Note that the OAM spectra are performed over the projections over the y polarization (those over the x polarization give similar results). The OAM spectrum of each beam results from the integration along the divergence angle, and each one is normalized independently.
