Harmonic Generation and Nonlinear Propagation: When Secondary Radiations Have Primary Consequences

• Published in: Physical review letters 2014-05, Vol.112 (20), Article 203902
• Main Authors: Béjot, P., Karras, G., Billard, F., Hertz, E., Lavorel, B., Cormier, E., Faucher, O.
• Format: Article
• Language: English
• Subjects: Channels; Harmonic generations; Harmonics; Ionization; Mathematical models; Nonlinearity; Pulse propagation; Three dimensional
• ISSN: 0031-9007; 1079-7114
• DOI: 10.1103/PhysRevLett.112.203902

In this Letter, it is experimentally and theoretically shown that weak odd harmonics generated during the propagation of an infrared ultrashort ultraintense pulse unexpectedly modify the nonlinear properties of the medium and lead to a strong modification of the propagation dynamics. This result is in contrast with all current state-of-the-art propagation model predictions, in which secondary radiations, such as third harmonic, are expected to have a negligible action upon the fundamental pulse propagation. By analyzing full three-dimensional ab initio quantum calculations describing the microscopic atomic optical response, we have identified a fundamental mechanism resulting from interferences between a direct ionization channel and a channel involving one single ultraviolet photon. This mechanism is responsible for wide refractive index modifications in relation with significant variation of the ionization rate. This Letter paves the way to the full physical understanding of the filamentation mechanism and could lead to unexplored phenomena, such as coherent control of the filamentation by harmonic seeding.