Competition between third-order nonlinear processes in the normal and anomalous dispersion regions of femtosecond pump laser pulses propagating in distilled water

The supercontinuum and third harmonic generation by focused infrared femtosecond laser pulses in distilled water in its normal and anomalous dispersion regions has been studied. Competition between the corresponding third-order nonlinearities has been detected: for pump wavelengths of 900–1200 nm (in the normal dispersion region), supercontinuum with the spectrum broadened predominantly to the blue region is generated. It has been found that 1300-nm femtosecond laser pulses propagating through the anomalous water dispersion region generate the third harmonic with the spectrum broadened to the red region. Saturation and reduction of the output of the third harmonic at a wavelength of 1300 nm with increasing pulse energy have been attributed to deterioration of phase matching as a result of ionization of the medium, which facilitates supercontinuum generation insensitive to phase matching.