Control of terahertz photoelectron currents generated by intense two-color laser radiation interacting with atoms

Quantum-Mechanical Description of Ionization-Induced Generation of Tunable Mid-Infrared Pulses

“…It is due to the fact that the Coulomb correction to the action depends essentially on the final momentum of the photoelectron in multiphoton regime. The account of this dependence can be made on the basis of imaginary time method used in [7,9] for the calculation of residual current density excited by two-color laser pulse. Unlike the phase dependences, the analytical result for maximum of time derivative of low-frequency current density (corresponding to the optimum phase) is, apparently, accurate throughout the full range of the Keldysh parameter.…”

“…This can be used to generate short pulses of mid-infrared radiation [4]. The low-frequency current density excited during gas ionization by a two-color laser pulse has been previously calculated analytically and numerically with the help of semiclassical and quantum-mechanical approaches [1][2][3][4][5][6][7][8][9]. The semiclassical approach is based on the solution of the hydrodynamic equation for the electron current density and the equation for the density of free electrons with a quasi-static probability of tunneling ionization per unit time [10].…”

Bright single-cycle terahertz source based on gas cells irradiated by two-color laser pulses

“…The physical mechanism of ω − 2ω THz generation is well understood on the singleatom level: a two-color laser field generally generates asymmetric photoelectron momentum distributions, so that after the averaging over fast oscillations with the frequencies ω and 2ω and over the distribution, the electron current does not vanish, in contrast to the case of a quasi-monochromatic field [22,23,24,25]. The collective response of a medium ionized by bichromatic fields is less studied owing to a high complexity of the problem.…”

Manipulation by Photoelectron Currents for the Generation of Terahertz Light Pulses

“…It was shown in particular that the configuration with parallel polarizations leads to higher photoelectron currents and THz signals than the one where the polarization directions are orthogonal. The main disadvantage of the scheme with linear polarizations is connected to the fact that the asymmetry of photoelectron distributions is maximal when the electric fields of the two components are phase shifted by /2, so that the enhancement in the ionization rate due to the presence of the second harmonic is minimal (see, e.g., [9,14] for details). As a result, the average photoelectron momentum 0 , which can be acquired within this scheme, appears proportional to the vector potential of the second field at the time instant when the first field has a maximum:…”

“…Ionization of argon is considered. Sharp spikes on the curves result from the channel closing effect taking place with the growth of the total intensity; see [14] for details of the calculation.…”