Third-Harmonic Generation and Third-Order Frequency Mixing

Third-harmonic generation at interfaces with femtosecond pulses: self-focusing contribution and nonlinear microscopy

“…This behavior is related to the Gouy phase shift of radians the Gaussian beam experiences when passing through the focus position and, this effect is three times higher for the third- order polarization compared to the fundamental beam, 42 Fig. 2.6.…”

“…11 Also, one can find alternative explanation 44 or new research 45 It is also important to mention that although, in this chapter, the polarization state of the field was not taken into account in the theoretical development for harmonic generation, such consideration would lead to a more general result which presents a significant consequence: there is no THG from a circularly polarized fundamental beam in an isotropic medium. This is related to the symmetry properties of the third-order susceptibility tensor elements and the electric field components 42 and, it is normally useful in order to suppress unwanted nonlinear processes when two or more effects can occur simultaneously. Nonlinear Refractive Index and Self-focusing Effect…”

“…Thus, the 90 THG at interfaces with femtosecond pulses: self-focusing contribution and nonlinear microscopy polarization has no third-harmonic content. 35,42 Until now, we have used amplitude modulation with an approximately sinusoidal amplitude modulation where the beam irradiance oscillates between two limits, the maximum irradiance and almost zero. Now, the modulation is done controlling the polarization state of the beam (by phase modulation) using the SLM.…”