Upper Bound to the Orbital Angular Momentum Carried by an Ultrashort Pulse

2019

Opt. Lett.

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We describe the coupling between orbital angular momentum (OAM) and temporal degrees of freedom in pulsed Laguerre-Gauss beams. The effects of this coupling are to increase significantly the duration of few-cycle pulses when the OAM carried by the pulse is large, and to enhance spatiotemporal couplings. Contrary to other detrimental but retrievable effects such as spatial, group velocity and topological charge dispersions in these pulses, OAM-temporal coupling effects are unavoidable, and have therefore an impact in applications such as OAM-based optical communications, or in the generation of vortex-carrying attosecond pulses.

mentioning

confidence: 99%

Effects of orbital angular momentum on few-cycle and sub-cycle pulse shapes: coupling between the temporal and angular momentum degrees of freedom

2019

Opt. Lett.

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“…(5) and (6) the pulse temporal shape depends on the particular caustic surface ρ, but not on propagation distance. In [3], the caustic surface ρ F where the timeintegrated intensity, energy density, or fluence,…”

Section: Ultrafast Vortices and Previous Resultsmentioning

confidence: 99%

“…OAM-temporal coupling is a particular case of spatiotemporal coupling, say an azimuthal-temporal coupling, which seems to be rather more pronounced than the radial-temporal coupling in ultrashort Gaussian beams. In [3][4][5][6] the effects of OAM-temporal coupling have been described for the first time in ultrafast vortices shaped as pulsed Laguerre-Gauss (LG) beams, commonly used in the experiments, and also shaped as pulsed Bessel beams, or diffractionfree X-waves. These effects are reviewed in [36], where it turns out that the OAM-temporal coupling manifests itself with different effects in different parts of the vortex.…”

Section: Introductionmentioning

confidence: 99%

Effects of the Coupling between the Orbital Angular Momentum and the Temporal Degrees of Freedom in the Most Intense Ring of Ultrafast Vortices

2020

Applied Sciences

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It has been recently shown that the orbital angular momentum (OAM) and temporal degrees of freedom in ultrafast (few-cycle) vortices are coupled. This coupling manifests itself with different effects in different parts of the vortex, as has been shown for the ring surrounding the vortex where the pulse energy is maximum, and also in the immediate vicinity of the vortex center. In may applications, however, the ring of maximum energy is not of primary interest, but that where the pulse peak intensity is maximum, which is particularly true in nonlinear optics applications such as the experiments with ultrafast vortices exciting high harmonics and attosecond pulses carrying also OAM. This article describes the effects of the OAM-temporal coupling at the ring of maximum pulse peak intensity, which does not always coincide with the ring of maximum pulse energy. We find that there exists an upper bound to the magnitude of the topological charge that an ultrafast vortex with prescribed pulse shape at its most intense ring can carry, and vice versa, a lower bound to the duration of the pulse at the most intense ring for a given magnitude of the topological charge. These bounds imply that with a given laser source spectrum, the duration of the synthesized ultrafast vortex increases with the magnitude of the topological charge. Explicit analytical expressions of ultrafast vortices containing these OAM-temporal couplings are given that can be of interest in a variety of applications, particularly in the study of their propagation and interaction with matter.

“…Another important issue is the duration of the individual pulses in the helical structure. As recently found, [7,8] a pulsed vortex with well-defined topological charge, i. e., without topological charge dispersion, must be longer than a certain minimum value determined by the topological charge. Helical pulses are superpositions of pulsed vortices with carrier frequencies in a frequency comb and with topological charges varying linearly with frequency, and therefore present topological charge dispersion.…”

Section: Introductionmentioning

confidence: 84%

“…The above upper bound for the pulse bandwidth implies that an arbitrarily short pulse cannot carry a vortex of the topological charge l, but there is lower bound to its duration [7,8]. As shown below, the dispersion or uncertainty in the topological charge inherent to the helical pulses will allow to beat these upper and lower bounds of the spectral bandwidth and pulse duration.…”

Section: Cylindrically Symmetric Pulsed Vorticesmentioning

confidence: 97%

Attosecond helical pulses

2019

Phys. Rev. A

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We find a solution of the wave equation in the paraxial approximation that describes the attosecond pulses with spatiotemporal helical structure in the phase and in the intensity recently generated by means of highly nonlinear optical processes driven by visible or infrared femtosecond vortex pulses. Having a simple analytical model for these helical pulses will greatly facilitate the study of their predicted applications, particularly their interaction with matter after their generation. It also follows from our analysis that the topological charge dispersion inherent to helical pulses allows to beat the minimum duration to which a pulsed vortex without charge dispersion is limited.