# Cascade Excitation of SRS Components

In conclusion, a brief mention should be made of peculiarities of SRS manifestation with regard for the cascade excitation of the Stokes components in the medium. The results of numerical solution of the first three equation of system (4.54) for the power and the effective radius of the beam are shown in Figure 4.12. The parameters of calculation were chosen to correspond to the OIL radiation propagating along the horizontal high-altitude path at *G* =* 200, *L =* 0.17, and *a _{n} =* 0.

It follows from Figure 4.12 that once some characteristic SRS length L_{R1}, which corresponds to the threshold G_{1}, is achieved, the marked growth of the power and radius of the first Stokes component begins with the simultaneous depletion of the main wave power. At the distance *L _{R}* 2, the power of the Stokes signal at the frequency

*w_*attains the saturation with the level close to the limiting value of the conversion coefficient pR

_{1}^{1}™. From this time, the amplification of the second Stokes component (o>_

_{2}) occurs due to nonlinear polarization induced by the field of the first Stokes component, which, in its turn, begins to deplete, and so on.

As a result, the final value of the conversion coefficient *p _{R}* at the cascade amplification of the two Stokes components appears to be lower than that at the two- photon SRS due to energy losses in the medium to excitation of optical phonons first by the main radiation and then by the field of the first Stokes component. The limiting level of the SRS conversion, which can be achieved in this n-cascade process, is, obviously,

*pR^*/o>

^{3}* = w_{n}_{0}. In the considered case of only two Stokes components and the oxygen laser radiation, we get that

*р^ <*41%.