Optical third-harmonic generation using ultrashort laser pulses

Abstract

To better predict optical third-harmonic generation ͑THG͒ in transparent dielectrics, we model a typical ultrashort pulsed Gaussian beam, including both group velocity mismatch and phase mismatch of the fundamental and harmonic fields. We find that competition between the group velocity mismatch and phase mismatch leads to third-harmonic generation that is sensitive only to interfaces. In this case, the spatial resolution is determined by the group velocity walk-off length. THG of modern femtosecond lasers in optical solids is a bulk process, without a surface susceptibility, but bears the signature of a surface enhancement effect in z-scan measurements. We demonstrate the accuracy of the model, by showing the agreement between the predicted spectral intensity and the measured third-harmonic spectrum from a thin sapphire crystal.

Influence of self-focusing of ultrashort laser pulses on optical third-harmonic generation at interfaces

“…This unbalances the TH generated at the entrance and exit interfaces. Other authors also observed such asymmetry [11,12], but none of them considered self-focusing of light for its explanation.To fully understand the results presented later, we consider the usual THG cubic dependence on the fundamental beam irradiance [13], which depends on the beam waist radius: …”

“…This unbalances the TH generated at the entrance and exit interfaces. Other authors also observed such asymmetry [11,12], but none of them considered self-focusing of light for its explanation.…”

Coherence-modulated third harmonic generation for vibrational spectroscopy: a theoretical treatment

“…The probe pulse induces an oscillating polarization density at ω 3 3ω 1 and generates a TH pulse [26][27][28][29]:…”

Reference free Chi 3 dispersion measurements in planar tantalum pentoxide waveguides

“…This is in contrast to other processes such as degenerate four-wave mixing and optical Kerr effect [23], where other competing nonlinear effects complicate the experimental analysis. THG has been observed in several materials including: BIBO (Bismuth triborate, 6 3 O BiB ) [24], thin sapphire crystals [25], fused silica [26], carbon nanotubes [27], and other types of single crystals [28].…”