A high power isolator for the 10 micron region employing interband Faraday rotation in germanium
At 1.06 p, the nonlinear susceptibility of Cs vapor is determined almost entirely by interaction between the 16s > = 10 > ground state andthe16p> = 11 > and17s> 3 12> levels. We have shown that in the case of linearly polarized light, the nonlinear susceptibility can be analyzed into two distinct contributions.' The predominant one arises from the polarization poz( t ) due to the two photon resonance between 16s > and 17s >. The other term, which is also negative at 1.06 p , arises from induced  population changes between the 16s > and 16p> levels, and is analogous to the nonlinear refractive effects observed by Grischkowsky and Armstrong.' In this experiment, where the pulses are much shorter than the inverse linewidth of 16p>, the nonlinear contribution to the refractive index becomes amplifier chain.