I want better understand the physics of this phenomenon and develop relevant intuition. If the linear and nonlinear susceptibility parameters depend on the polarization state (Linear or circular), for which polarization we must expect higher value of the susceptibility parameters and why? Thank you in advance!
Dear Vladimir! You have raised complicated question because the true answer depends upon the state of material and interaction time with the polarized light. For example in the case of the atomic ensemble some electronic transitions are permitted only for circularly polarized light due to selection rules on the orbital number. In the case of birefringence crystal, one or two wave propagation (and interaction) will depend on from the mutual orientation of the optical axes and the linear polarization vector. In the case of solid solution of the anisotropic organic molecules without ordering the excited fluorescence will be polarized the same state as the light beam used for excitation. The same time the liquid solution of the similar molecules will discover no linear polarization under the similar polarized excitation, but their pulse excitation (nano,-picosecond duration) are followed the polarized fluorescence. At nonlinear absorption and amplification under the strong pumping of the similar dye solution, we can observe 100% polarized emission of lasing or ASE.The strong linear pulse polarized light can create the nonlinear response known as optical Kerr effect with subpicosecond relaxation time. The similar results can not be realized with pulse circular polarized emission. You see, Vladimir, that there are many effects depending on the polarization type of light, but with taking into account some boundary conditions. I hope that some benefit my info will offer You.
Vladimir, Dr. Tikhonov is absolutely right, you cannot develop any intuition unless you specify your particular case. One thing to remember, though, is that susceptibility is coefficient connecting polarization produced in material to the applied EM field. That basically means that higher susceptibility will be observed for directions where it is "easier to electrons to flow" under the action of the external electric field. That is, of course, extremely oversimplified explanation, but it does cover the physical essence of the phenomena. Taking it to an extreme, you can envision a wire-grid polarizer as a crystal whose susceptibility is infinite along the wires, and zero in orthogonal direction.
Good luck
I once was told in grad school, that susceptibility is better expressed as "polarizability" of a given material. helped me at the time.
Linear as well as nonlinear susceptibility are the intrinsic material parameters, independent of external radiation. Linear susceptibility related to the refractive index of the material , - which may be a constant for the isotropic materials or second rank tensor in the case of anisotropic materials. The best known is the iceland spar.
When talk about nonlinear susc., - the tensor rank becomes higher. So, it is a parameter linking the input wave with output wave. The output field value depends, of corse, on the polarisation and directions of the input wave. You have select special crystallographic axes to optimise the output.
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