A possibility to greatly enhance frequency-conversion efficiency of stimulated Raman scattering is shown by making use of extraordinary properties of three-wave mixing of ordinary and backward waves. Such processes are commonly attributed to negative
-index plasmonic metamaterials. This work demonstrates the possibility to replace such metamaterials that are very challenging to engineer by readily available crystals which support elastic waves with contra-directed phase and group velocities. The main goal of this work is to investigate specific properties of indicated nonlinear optical process in short pulse regime and to show that it enables elimination of fundamental detrimental effect of fast damping of optical phonons on the process concerned. Among the applications is the possibility of creation of a family of unique photonic devices such as unidirectional Raman amplifiers and femtosecond pulse shapers with greatly improved operational properties.
A concept of a family of unique backward-wave photonic devices, such as frequency up and down converting nonlinear-optical mirrors, sensors, modulators, filters and amplifiers is proposed. Novel materials are considered, which support coexistence of
ordinary and backward waves and thus enable enhanced nonlinear-optical frequency-conversion processes. Particular properties of short-pulse regime are investigated.
The Raman gain of a probe light in a three-state $Lambda $-scheme placed into a defect of a one-dimensional photonic crystal is studied theoretically. We show that there exists a pump intensity range, where the transmission and reflection spectra of
the probe field exhibit textit{simultaneously} occurring narrow peaks (resonances) whose position is determined by the Raman resonance. Transmission and reflection coefficients can be larger than unity at pump intensities of order tens of $mu$W/cm$^{2}$. When the pump intensity is outside this region, the peak in the transmission spectrum turns into a narrow dip. The nature of narrow resonances is attributed to a drastic dispersion of the nonlinear refractive index in the vicinity of the Raman transition, which leads to a significant reduction of the group velocity of the probe wave.
