Coherent intramodal Raman gain suppression at high pump intensities in gas-filled photonic crystal fibres

Stimulated Raman scattering is coherently suppressed if the rate of phonon creation is exactly balanced by the rate of phonon annihilation, a prediction first made by Bloembergen and Shen in 1964 [1]. Viewed classically, this occurs when the fringe patterns created by the interference of pump-Stokes and pump-anti-Stokes signals cancel each other out. It has been recently shown that gas-filled hollow-core photonic crystal fiber (HC-PCF), pumped in the vicinity of the zero-dispersion point (ZDP), is an ideal vehicle for observing gain suppression. The ultralong path-lengths and the well-controlled dispersion permit dramatic suppression of the effective intramodal Raman gain for the fundamental core mode [2, 3], resulting in strong enhancement of intermodal scattering from the pump to a Stokes signal in a higher-order core mode.