Group velocity self-matching in noncollinear optical parametric generation with a type-Ⅰ phase-matched BBO crystal

Abstract

Noncollinear parametric superfluorescence (NPS) is obtained in the visible regio n by pumping a type-Ⅰ phase-matched BBO crystal with the second harmonic of an amplified Ti:sapphire laser at 1kHz repetition rate. The variation of the noncol linear angle and the wavelength at the peak intensity of the NPS with the phase- matched angle is studied, and the variations of the group velocity mismatch (GVM ) with the noncollinear angle and the phase-matched angle in the three-wave inte raction is calculated theoretically. The results indicate that the type-Ⅰ phase -matched NPS ring is centrosymmetric with respect to the pump beam on the observ ation screen. Along the NPS direction at the peak intensity, the GVM is minimal and the effective interaction length is maximal for the three waves. The angular distribution of the NPS intensity is ascribed to phase velocity and group veloc ity self-matching among interacting pulses. The theory and the experiment provid e an ideal geometrical model for reducing the GVM between three waves, and provi de a theoretical guidance and experimental verification for obtaining parametric pulses with higher gain and shorter duration in femtosecond optical parametric amplification.