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(a) The CEP shift (blue solid line) around the focus of a few-cycle pulse in vacuum; (b) the CEP shift (blue solid line) in the interaction region between an intense few-cycle laser field and N2 molecules, and the density of molecule number of N2 (red dotted dashed line). z is the propagation coordinate.
THz waveform as a function of plasma length by few-cycle laser fields with the initial CEP of (a)–(d): δφ 0 = 0.0π, 0.2π, 0.4π, and 0.6π, respectively.
The calculated THz amplitude as a function of plasma length and the initial CEP of few-cycle pulses with the input energy of (a) 250 μJ and (b) 400 μJ, respectively, and the extracted inversion positions of THz emission in a step-size of 0.1π, for the energy of (c) 250 μJ and (d) 400 μJ, respectively.
(a) The calculated offset of zero THz dependence on the CEP along the front part of filament, at the input energy of 250 μJ and 400 μJ, respectively. Inset shows the THz yield as function of CEP at position of A (z = −8.4 mm) of 400 μJ; (b) the calculated initial CEP value by which the inversion of THz emission disappears at the beginning of air plasma under different input energies of 200 μJ–900 μJ.
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