Quasi-phase matching SRS generation. Nikolai S. Makarov, State Institute of Fine Mechanics and Optics, Victor G. Bespalov, Russian Research Center "S. I. Vavilov State Optical Institute" In the present paper we analyzed the increasing of anti- Stokes SRS generation efficiency in conditions of quasi-phase matching in media with periodically changing of parameters of the third order (Raman) nonlinearity. For three waves SRS approximation (pump, Stokes and anti- Stokes components) in steady-state regime the system of the equations for complex amplitudes of interacting waves was numerically solved. The thickness of layers was optimized for effective energy conversion from pump and Stokes waves to the anti-Stokes component and correspondingly the conditions of quasi-phase matching was fulfilled. The numerical analysis of the system has shown that the conversion efficiency into the anti-Stokes component in layered gaseous Raman media (for example hydrogen, deuterium, methane with glass or crystal plates) reached ~35 %, and the intensity of output anti-Stokes component is compared to the intensity of output Stokes component.

Second harmonic generation in condition of quasi-phase matching. Condition of quasi-phase matching at generation of anti-Stokes SRS radiation.

System of equations for complex amplitudes of interacting waves A j :  – waves mismatching, g – steady-state Raman gain coefficient,  i – frequencies of interacting waves. In this system the waves mismatching and Raman gain were the functions of coordinate for nonlinear (  (3)  0) and linear (  (3) =0) layers.

Dependence of anti-Stokes SRS generation efficiency from Stokes/pump waves intensity ratio on an entrance in Raman-active media. Hydrogen,  = 3.84 rad/cm, g = 3.0 cm/GW. The value of optimum ratio depended from waves mismatching and steady-state Raman gain coefficient. While waves mismatching decreased the ratio value decreased too, while steady-state Raman gain coefficient increased the ratio value decreased for low waves mismatching and increased for high waves mismatching.

Quasi-phase matching SRS generation in hydrogen.  = 3.84 rad/cm, g = 3.0 cm/GW, I s (0) = GW/cm 2, efficiency = 30%. 1 - quasi-phase matching, 2 - without (quasi-) phase matching, 3 - phase matching

Length of active and passive zone versus zone number in layered media. H2H2 Ba(NO 3 ) 2

Dependence of characteristic zone length from waves mismatching in layered media. Our studying showed that it is possible to approximate this dependence as L = *  We also found that with increasing of waves mismatching structure become more periodical.

- For each "configuration" of media our numerical simulation carried out the optimum ratio of input Stokes/pump intensity with maximal efficiency of anti-Stokes SRS generation. - Our study showed that efficiency of anti- Stokes SRS generation with condition of quasi-phase matching was much higher than at simple SRS focusing in media. The maximum conversion efficiency reached ~ 35 %. - There is a maximal value of pump intensity for realization of QPM which is connected with higher Stokes amplification. - We established that with wave mismatching increasing the characteristic length of layers strongly decreased, it caused difficulties at realization of this method for large values wave mismatching (>150 rad/cm). Conclusion