Abstract
Chirped dynamically assisted pair production in spatial inhomogeneous electric fields is studied by the Dirac-Heisenberg-Wigner formalism. The effects of the chirp parameter on the reduced momentum spectrum, the reduced total yield of the created pairs for either low or high frequency one-color field and two-color dynamically assisted combinational fields are investigated in detail. Also, the enhancement factor is obtained in the later two-color field case. It is found that for the low frequency field, no matter whether it is accompanied by the other high frequency field, its chirping has a little effect on the pair production. For the one-color high frequency field or/and two-color fields, the momentum spectrum exhibits incomplete interference and the interference effect becomes more and more remarkable as chirp increases. We also find that in the chirped dynamically assisted field, the reduced total yield is enhanced significantly when the chirps are acting on the two fields, compared with that the chirp is acting only for the low frequency strong field. Specifically, by the chirping, it is found the reduced pair number is increased by more than one order of magnitude in the field with a relative narrow spatial scale, while it is enhanced at least two times in other case of field with larger spatial scales or even in the quasi-homogeneous region. We also obtain some optimal chirp parameters and spatial scales for the total yield and enhancement factor in different scenarios of the studied external field. These results may provide a theoretical basis for possible experiments in the future.
Highlights
Dirac’s equation predicted the existence of positrons [1,2] and implied the virtual particles fluctuation inherent in the quantum electrodynamics (QED) vacuum which further unveiled rich and novel physical phenomena [3]
We explore the reduced momentum spectrum or/and the reduced total yield of created particles as well as enhancement factor for several spatial scales, for the following cases: (i) without chirp (b1 1⁄4 b2 1⁄4 0), (ii) chirping is only for E1sðx; tÞ (b1 ≠ 0, b2 1⁄4 0), (iii) chirping is only for E2wðx; tÞ (b1 1⁄4 0, b2 ≠ 0), and (iv) chirping is for both E1sðx; tÞ and E2wðx; tÞ (b1 ≠ 0, b2 ≠ 0)
It is noted that the momentum spectrum peaks obtained by Eðx; tÞ without chirp are smaller than that in the single field E2wðx; tÞ with the maximum chirp b2 1⁄4 0.9ω2=τ in the last section [Fig. 3(d)] which indicates that the chirp parameter plays an important role in the momentum distribution
Summary
Dirac’s equation predicted the existence of positrons [1,2] and implied the virtual particles fluctuation inherent in the quantum electrodynamics (QED) vacuum which further unveiled rich and novel physical phenomena [3]. As an important step to increase the pair production, Schützhold et al [31] proposed dynamically assisted Schwinger mechanism, which is the combination of a low frequency strong field with a high frequency weak field. They pointed out that the pair creation rate is. Frequency chirp effects are widely studied because they affect the momentum spectra and the total particle number under the time dependent field [32,33] and spatial inhomogeneous oscillating electric field [28]. We use the DHW formalism to investigate pair production in frequency chirped dynamically assisted electric field with spatial inhomogeneity.
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