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Register a new userPair production in laser fields: finite size effects
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We discuss pair creation in a strong laser background. Using lightfront field theory, we show that all the physics is contained in the lightfront momentum transfer from the laser, and probe, to the produced pair. The dependence of this momentum transfer on the geometry of the laser leads to resonance and diffraction effects in pair production spectra. The lightfront approach naturally explains the interpretation of laser-stimulated pair production as a multi-photon process creating pairs of an effective mass.
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We consider stimulated pair production employing strong-field QED in a high-intensity laser background. In an infinite plane wave, we show that light-cone quasi-momentum can only be transferred to the created pair as a multiple of the laser frequency, i.e. by a higher harmonic. This translates into discrete resonance conditions providing the support of the pair creation probability which becomes a delta-comb. These findings corroborate the usual interpretation of multi-photon production of pairs with an effective mass. In a pulse, the momentum transfer is continuous, leading to broadening of the resonances and sub-threshold behaviour. The peaks remain visible as long as the number of cycles per pulse exceeds unity. The resonance patterns in pulses are analogous to those of a diffraction process based on interference of the produced pairs.
The pair-production process in the presence of strong linearly polarized laser fields with a subcycle structure is considered. Laser pulses with different envelope shapes are examined by means of a nonperturbative numerical technique. We analyze two different flat envelope shapes and two shapes without a plateau for their various parameters including the carrier-envelope phase. The resonant Rabi oscillations, momentum distribution of particles created, and total number of pairs are studied. It is demonstrated that all these characteristics are very sensitive to the pulse shape.
We study the time-dependent solitonic gauge fields in scalar QED, in which a charged particle has the energy of reflectionless P{o}sch-Teller potential with natural quantum numbers. Solving the quantum master equation for quadratic correlation functions, we find the exact pair-production rates as polynomials of inverse square of hyperbolic cosine, which exhibit solitonic characteristics of a finite total pair production per unit volume and a non-oscillatory behavior for the entire period, and an exponentially decaying factor in asymptotic regions. It is shown that the solitonic gauge fields are the simplest solutions of the quantum master equation and that the back-reaction of the produced pairs does not destabilize the solitonic gauge fields.
Deep understanding of photon polarization impact on pair production is essential for the efficient creation of laser driven polarized positron beams, and demands a complete description of polarization effects in strong-field QED processes. We investigate, employing fully polarization resolved Monte Carlo simulations, the correlated photon and electron (positron) polarization effects in multiphoton Breit-Wheeler pair production process during the interaction of an ultrarelativistic electron beam with a counterpropagating elliptically polarized laser pulse. We showed that the polarization of e^-e^+ pairs is degraded by 35%, when the polarization of the intermediate photon is resolved, accompanied with an approximately 13% decrease of the pair yield. Moreover, the polarization direction of energetic positrons in small angle region is reversed, which originates from the pair production of hard photons with polarization parallel with electric field.
Electron-positron pair production in strong electric fields, i.e., the Sauter-Schwinger effect, is studied using the real-time Dirac-Heisenberg-Wigner formalism. Hereby, the electric field is modeled to be a homogeneous, single-pulse field with subcritical peak field strength. Momentum spectra are calculated for four different polarizations - linear, elliptic, near-circular elliptic or circular - as well as a number of linear frequency chirps. With details depending on the chosen polarization the frequency chirps lead to strong interference effects and thus quite substantial changes in the momentum spectra. The resulting produced pairs number densities depend non-linearly on the parameter characterizing the polarization and are very sensitive to variations of the chirp parameter. For some of the investigated frequency chirps this can provide an enhancement of the number density by three to four orders of magnitude.
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