Modified attenuated total reflection for the fast and routine electrooptic measurements of nonlinear optical polymer thin films

Abstract

In the course of developing EO polymers, a convenient and fast method to obtain the electrooptic (EO) coefficients, r33 and r13, is highly desirable. Some of the existing EO measurement techniques such as Fabry-Perot interferometry(1) and ellipsometry(2) require metal deposition and electrode processing for each test sample. Therefore, they are not suited for daily sample testing. Second harmonic generation (SHG) is an indirect method to measure the EO coefficients(3). It is usually performed with 1.064 Nd:YAG laser and encounters difficulties with polymers that contain high µβ chromophores because these chromophores usually have red-shifted absorption peaks that causes the Kleiman symmetry, a fundamental assumption of this technique, to break down. Attenuated total reflection (ATR) can directly measure the EO coefficients with no restriction on the wavelength of the absorption peak. One measurement scan provides the refractive index, the thickness, and an EO coefficient. Typically, the thin film electrode in contact with the test sample is made of Au or Ag in conventional ATR techniques(4). These metal thin films are soft and not durable for repeated measurements. The curve fitting algorithm for data processing(4, 5) is also inconvenient for fast sample evaluation. In this paper, a modified ATR technique for routine EO measurement is presented which does not require electrode preparation for each test sample and uses a simple algorithm for data processing.