Regular Article – Atomic Physics
Harmonics generated in circularly polarized laser fields: a study on spin angular momentum conservation
Department of Physics, Shanghai Normal University, 200234, Shanghai, China
2 International School for Optoelectronic Engineering, QiLu University of Technology (Shandong Academy of Science), 250353, Shandong, China
Accepted: 10 January 2023
Published online: 27 January 2023
Harmonics generated from the electronic transition among continuum states are studied by a quantum scattering theory. The analytical formulas of the harmonics generated in one- and two-color circularly polarized (CP) laser fields are obtained rigorously. The harmonic generation amplitude is described by a pair of phased generalized Bessel functions, by which the conservation relations of the spin angular momentum are derived in a solid base and in a straightforward way. It is found that, owing to the spin angular momentum conservation, high-order harmonics cannot be generated in the one-color CP fields, but can be generated in the bichromatic CP fields. To a given harmonic order, two generation channels exist: one generates right CP harmonic, while the other generates left CP harmonic. When the driving CP modes are of opposite helicity, the generated right CP harmonic is of the comparable strength to the left CP harmonic. When the driving CP modes are of same helicity, the harmonic with the same helicity as the driving fields is much stronger than that with the opposite helicity to the driving fields. The selection rules of harmonics are different in these two kinds of bichromatic CP driving fields.
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