Self-channeling of high-power laser pulses through strong atmospheric turbulence

Abstract

We present a new paradigm for truly long-range propagation of high-power laser pulses through strong atmospheric turbulence. A form of nonlinear self-channeling is achieved when the laser power is close to the self-focusing power of air and the transverse dimensions of the pulse are smaller than the coherence diameter of turbulence. In this mode, nonlinear self-focusing counteracts diffraction, and turbulence-induced spreading is greatly reduced. Furthermore, the laser intensity is below the ionization threshold so that multiphoton absorption and plasma defocusing are avoided.Simulations show that the pulse can propagate many Rayleigh lengths (several kilometers) while maintaining a high intensity. In the presence of aerosols, or other extinction mechanisms that deplete laser energy, the pulse can be chirped to maintain the channeling.

Deep-learning-based high-resolution recognition of fractional-spatial-mode-encoded data for free-space optical communications

“…In the case of strong atmospheric turbulence, an active method based on ultrashort high-intensity laser filaments can produce a cleared optical channel by opto-mechanically expelling the droplets out of the beam area 56 . Besides, it is possible to achieve long-range propagation by means of nonlinear self-channeling of high-power laser pulses 57 . Compared to the ordinary spatial modes of an integer mode index, fractional modes are much sensitive to the external perturbation.…”

Beating Optical-Turbulence Limits Using High-Peak-Power Lasers

“…For the self-channeling condition to be met the beam must remain smaller than the inner scale of turbulence or the transverse coherence length over the entire propagation range [12]. Probability distributions of the beam size for varying turbulence strength are plotted in Figure 4.…”

“…The discussion to this point has been limited to transverse beam properties; however, the broadband nature of the pulse requires an examination of the temporal dynamics. As pointed out in [12], temporal compression is necessary to maintain the self-channeling condition when absorption, scattering, and diffractive losses are present. We observed instances in which the beam undergoes almost purely linear compression of the negatively chirped pulse due to GVD, as well as instances where pulse splitting is present, a clear signature of self-phase modulation.…”

“…For linear propagation over a long distance, natural diffraction increases the beam size to a point where this condition eventually can no longer be met. However, this is not the case for a nonlinear self-channeling beam, which can maintain its size over long distances by using nonlinear self-focusing to balance out diffraction [12,13]. This condition is met when the peak power is equal to the critical power in air, ∼5GW [14].…”

Analytical Description of the Dynamics of Planar Pulses Propagating in the Mode of Tunnel Ionization

“…Several mechanisms have been proposed for stabilizing signals when D > 1: saturating nonlinearity [6], competing nonlinearities [7], higher-order diffraction or dispersion [8], gradient waveguide [9], and second-harmonic generation [10]. It was shown [11][12][13][14][15][16][17][18] that ionization can also stabilize a signal, due to the balance between self-focusing, diffraction, and plasma divergence. It is known that ionization shifts the pulse spectrum toward higher frequencies [19][20][21] due to the generation of free electrons.…”