Why does second order susceptibility become zero in centrosymmetric media?

[eahaidar]

Hello everyone I just want to ask why In a centrosymmetric media the media doe not change why going from r to -t r is a position vector thus Second order susceptibility becomes zero ?? Thank you

 

[UltrafastPED]

A complete explanation can be found in this lecture on nonlinear spectroscopy:
http://www.mitr.p.lodz.pl/evu/lectures/Vauthey.pdf

Or see this textbook explanation: "Introduction to Nonlinear Optics", chap. 1 and 3.

http://books.google.com/books?id=X8...rosymmetric nonlinear optics tutorial&f=false