Two-dimensional spectroscopy of electric birefringence relaxation in frequency domain: Measurement method for second-order nonlinear after-effect function

A new measurement method for second-order nonlinear after-effect function h as been developed. Theoretical calculation starting from a general time-evo lution equation connects nonlinear responses in time domain and frequency d omain and thus gives the nonlinear response to applied external field of ar bitrary form. In addition, it turns out in the frequency domain that the dc component of a second-order nonlinear response function corresponds to a l inear response function. For example, the dc component of the electric bire fringence relaxation is equivalent to the dielectric relaxation. This simpl e relation indicates an advantage of a frequency-domain measurement for non linear responses. As an example, the electric birefringence relaxation is m easured in two-dimensional frequency domain for aqueous solution of sodium poly(styrenesulfonate) to confirm the validity of the theoretical results. (C) 1999 American Institute of Physics. [S0021-9606(99)51308-1].