  We have developed an analytical model based on the perturbation theory in
order to study the optical propagation of two successive intense solitons in
hollow-core photonic crystal fibers filled with Raman-active gases. Based on
the time delay between the two solitons, we have found that the trailing
soliton dynamics can experience unusual nonlinear phenomena such as spectral
and temporal soliton oscillations and transport towards the leading soliton.
The overall dynamics can lead to a spatiotemporal modulation of the refractive
index with a uniform temporal period and a uniform or chirped spatial period.
