Dramatic suppression of Raman gain in hydrogen-filled hollow-core PCF

01.01.2016, 00:00

Newsletter 9

In 1964 Bloembergen and Shen predicted that gain in Raman-active media, i.e. the exponential amplification of Stokes signals down-shifted with respect to the pump frequency by a transition frequency of Raman-active molecules, could be coherently suppressed if the rates of phonon creation and annihilation exactly balance. This only occurs if synchronous, collective molecular oscillations, i.e., phonon coherence waves created by pump-to-Stokes scattering, are identical to those annihilated in pump-to-anti-Stokes scattering. In free space, this can only be accomplished over limited interaction lengths via non-collinear geometries. In contrast, by using a gas-filled kagomé-type hollow-core PCF, we demonstrate the first dramatic suppression of the Raman gain over long collinear path-lengths in hydrogen. This is achieved by operating close to the pressure-tunable zero dispersion point of the fibre, where the conditions for coherent gain suppression are fulfilled. Thus, at a precise pressure, generation of Stokes and anti-Stokes bands in the fundamental mode is entirely suppressed (see Figure), allowing other processes such spontaneous Raman scattering to be investigated in regimes of high luminosity. This study may have implications in quantum information and particle micromanipulation.

Contact: david.novoa(at)mpl.mpg(dot)de
Group: Russell Division
Reference: S. T. Bauerschmidt et al., Phys. Rev. Lett. 115, 243901 (2015).