Determination of the molecular distribution function of new Langmuir-Blodgett films by second harmonic generation

Summary form only given. One method for determining the nonlinear characteristics of materials consists of the study of Langmuir-Blodgett (LB) films prepared by the deposition of oriented monolayers on a glass substrate. When a powerful laser beam illuminates the substrate, two beams of second harmonic signal are generated, one originating from each of the substrate surfaces. As the phase of the second harmonic is determined by the phase of the incident pump, a phase mismatch exists between the two second harmonic beams, which are generated on opposite surfaces of the substrate. This phase mismatch is due to the difference of the refractive indexes of the substrate for pump and second harmonic beams. This will lead to their constructive or destructive interference depending upon the effective thickness of the substrate, which is defined by the pump beam incidence angle. Thus, changing the angle of the pump incidence one can obtain interference fringes, which are known as Maker fringes. Measuring these fringes, one can determine the nonlinear characteristics of the LB film.