摘要： Light beams may carry both a spin and an orbital angular momentum (OAM). While the former is associated to their polarization state, the latter stems from the geometrical properties of their wavefront. In their prototypical form, beams with OAM have “donuts-like” intensity profile and helicoidal wavefront, carrying integral multiples of ? as angular momenta. Since their “rediscovery” in the late 90’s, beams with OAM of visible wavelengths have found innumerable applications in optics, microscopy, quantum or information transfer. A major recent development was the generation of such beams with much smaller wavelengths – in the extreme ultraviolet (XUV) - using synchrotron sources, free electron lasers as well as high harmonic sources (HHG). In this latter case, it creates ultrashort XUV sources of beams with OAM, for time-resolved and femtosecond applications attosecond time scales. Remarkably, we showed that even though HHG is a non-perturbative process, the OAM transfer from the driving beam to the harmonics was purely parametric; i.e., the q-th harmonic – which can be thought as the upconversion of q infrared photons – carries q times the OAM of the driver [3, 4]. However, this rule limits severely the flexibility in choosing the OAM of the XUV emission. In this communication we present experiments that go beyond this simple scheme. If OAM transfer does behave in a parametric way, using two driving beams of different OAM should give us the control knob to fully tailor the harmonic emission. We show that this is indeed the case, using an extra “perturbing” beam to adjust at will the value of the OAM of the outgoing harmonics[2] (see figures). In a second part, we study how far this perturbative description can be taken. We observe that when increasing the perturbation, the yield of the higher perturbation orders can overwhelm the yield of the zeroth order. To explain this result, which seems to go against describing HHG as a parametric process, we derive a quantitative theory of HHG with two beams, based on the analysis of the wavefront of the global electric field at focus [1]. This reproduces the experimental results strikingly well, allowing us to gain a deeper understanding of the complex interplay of phenomena underlying the transfer of OAM in high-harmonic generation.