It is well documented that nonlinear optical systems can exhibit chaotic behavior. This behavior even appears in air when the light intensity is large enough. Chaotic behavior is well characterized by statistical means, because of sensitivity to initial conditions. Beam quality, đť‘€2 or the beam propagation parameter, is a key propagation parameter that is dependent on the spatial distribution of the optical field and deviations the medium makes from homogeneity or linearity. In order to better understand beam quality statistics for random fields in a nonlinear medium, an experimental system has been developed, and undergone initial testing. A Boston Micromachines Multi-DM 140 12x12 rectangular deformable mirror (DM) is used to induce phase screens on a 532nm visible beam, which then enters a lens-based beam profiling unit. Using computer controls and data pipelines, thousands of phase screened beams can be measured for beam quality automatically. Experimental testing shows stability of beam quality measurement across thousands of trials, and beam ensembles with long (of order beam size) coherence lengths to be feasible. Upon refinement of DM modeling with the insertion of a nonlinear medium the system can be made to test statistical models of nonlinear optics.
Naturally occurring self-lasing of a confined plasma discharge is used as a plasma diagnostic. Together with other readily measurable parameters such as discharge voltage and current, the laser radiation provides the necessary constraints for fitting the parameters of a plasma chemistry model. The model determines the plasma density, electron temperature and excited-state populations as functions of time and space and shows excellent agreement with experiments performed in a nitrogen-filled discharge tube. Plasma self-lasing has been observed in a form of a ring and has a corresponding annular plasma density profile. This profile was used as initial conditions for diffusion model that predicts parabolic density at later times. Analysis of the parabolic profile shows that it can be employed for optical guiding of laser beams with spot radius ~mm.
An intense laser pulse propagating through a near-critical density plasma is capable of generating a high peak current electron beam (~100kA) by means of a laser wakefield operating in the bubble regime. This beam drives surface currents on the sheath of the cavitation that produces large azithumal magnetic fields (~100 MG) and induces an on-axis electron current. These effects lead to a Z-pinch of the ambient plasma ions. Eventually the field confining the pinch relaxes and the ions explode radially due to self-repulsive forces. If this process occurs at a sharp exit gradient, the ions acquire some forward momentum consistent with the magnetic vortex acceleration mechanism. Fully 3D simulations indicate that the highest energy ions are emitted conically with a secondary lower energy ion beam accelerated on the axis.
This paper discusses an advanced target in the loop (ATIL) system with its performance based on a nonlinear phase conjugation scheme that performs rapid adjustment of the laser beam wavefront to mitigate effects associated with atmospheric turbulence along the propagation path. The ATIL method allows positional control of the laser spot (the beacon) on a remote imaged-resolved target. The size of this beacon is governed by the reciprocity of two counterpropagating beams (one towards the target and another scattered by the target) and the fidelity of the phase conjugation scheme. In this presentation we will present the results of the thorough analysis of ATIL operation, factors that affect its performance, its focusing efficiency and the comparison of laboratory experimental validation and computer simulation results.
Blast waves ignited in a supersonic flow are capable of producing density profiles useful for laser acceleration of electrons and ions. By using a ≈0.1 joule nanosecond laser as an igniter, and controlling the angle of incidence and timing of the ultra-intense femtosecond drive pulse, one can produce a variety of gas density profiles. A profile with an abrupt up-ramp followed by a gradual down-ramp leads experimentally to stable generation of 40 MeV electrons from a 10 TW drive pulse. A profile with a narrow high density region, and a steep density ramp on one side, is useful for magnetic vortex acceleration of ions. Simulations predict that such a profile can be generated from a laser ignited blast wave, and that 35 MeV protons are produced when a 100 TW pulse is focused into the shock front.
Recent theoretical work has provided new insight into the physics of Electro-Optic detection of ultrashort relativistic
electron beams.1 Typically, Electro-Optic detection has been restricted to bunches longer than ~ 100
fs. This limitation is due to the transverse optical (TO) phonon resonance that most Electro-Optic materials
exhibit in the THz range. Once the electron bunch profile becomes short enough so that a significant portion
of its frequency components reside above this resonance frequency, the temporal profile of the space charge field
begins to distort as it propagates through the crystal. This distortion becomes more significant as the bunch
becomes shorter and destroys the ability of current decoding techniques to resolve the original bunch profile.
It is possible to circumvent this issue by realizing that for these higher frequency components it is no longer
valid to rely on the formalism of Pockels effect. Instead, sum and difference frequency generation must be
taken into account. Using nonlinear three-wave mixing to describe the process, a new technique that promises
the order of magnitude increase in resolution necessary to measure the ultrashort bunches produced by laser
wakefield accelerators has been developed. This technique provides both phase and amplitude information about
the generated pulse from which, in principle, the temporal profile can be reconstructed.
In laser driven accelerators, the interaction of laser radiation with plasma leads to a variety of scattering mechansims.
The scattered radiation can be used to understand the wake structure and its effect on electron acceleration.
In the case of a resonantly driven quasi-linear wake, spectral broadening due to photon acceleration and deceleration
is related to the coupling of energy into plasma waves. Simultaneous time and frequency analysis of the laser
fields produces distinctive features in the photon phase space that give information on wake generation in long
plasma channels. The ponderomotive guiding center algorithm is advantageous for modeling such interactions
because it allows for averaging over optical cycles, and can be implemented in axisymmetric geometry. In the
case of the nonlinear wakes that are driven in the self-guided regime, a region of electron cavitation is formed,
which emits electro-optic shocks at the second harmonic of the drive laser. The form of this radiation can be
correlated with electron trapping.
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