Optical Second Harmonic Generation Analysis of Unrubbed Polyimide Surfaces as a Function of the Content of Steroidal Structure Side Chains

Abstract

Contribution of main chains and side chains of unrubbed polyimide films with steroidal structure side chains to second harmonic generation (SHG) response was studied by varying their molar fraction of side-chain diamine. The SHG intensity in P_in/P_out polarization (P-polarization input and P-polarization output) configuration does not depend strongly on the molar fraction. This indicates that both the main chains and side chains at the surface contribute similarly to the SHG intensity. The SHG intensity in S_in/P_out polarization configuration normalized by that of P_in/P_out polarization configuration was the smallest for the molar fraction of side-chain diamine of 0%. This fact indicates that the microscopic nonlinear dipoles are standing nearly upright at the surface of the film consisting only of the main chains, while their orientational spread is wider when the side chains are involved.