INDEX field dependence

Spatial intensity distribution of the interference field depends on the phase difference between the beams Sy = ki - kj (in vector notation) and their mutual angles 9 (where i,j are the beam index) as ... 

However, the linear response of a dielectric to an applied field is an approximation the actual response is non-linear and is of the form indicated in Fig. 8.6. The electro-optic effect has its origins in this non-linearity, and the very large electric fields associated with high-intensity laser light lead to the non-linear optics technology discussed briefly in Section 8.1.4. Clearly the permittivity measured for small increments in field depends on the biasing field E0, from which it follows that the refractive index also depends on E0. The dependence can be expressed by the following polynomial ... 

Examination of Eq. (6.21) shows that y(a>) is comprised of two terms that are proportional to c, 2 and that are associated with the traditional contribution to the susceptibility from state 11 ) and E2) independently, plus two field-dependent terms, proportional to a -j = c cje co /eia), which results front the coherent excitation of both II ) and E2) to the same total energy E = Ex + to) = E2+ to2. As a consequence, changing au alters the interference between excitation routes and allows for coherent control over the susceptibility. As in all bichromatic control scenarios, this control is achieved by altering the parameters in the state preparation in order to affect c1,c2 and/or by varying the relative intensities of the two laser fields. Note that control over y(ciy) is expected to be substantial if e(a>j)/e(cOj) is large. However, under these circumstances control over yfro,) is minimal since the corresponding interference term is proportional to e(a>t)/e(cQj). Hence, effective control over the refractive index is possible only at one of co( or >2. 

The nonlinear index of refraction is related to the applied electric field, E, through the electric-field-dependent susceptibility, Xen of a material. 

Birefringent samples have a refractive index that depends on the direction of the electric field in the light. They may be single crystals, or polycrystalline or amorphous polymers with oriented regions [23, 69]. Materials containing... 

---