Laser Probe of Surfaces of Bacteriorhodopsin Langmuir-Blodgett Films by the Method of Second Harmonic Generation

Abstract

Among the numerous methods of laser probing surfaces of Langmuir-Blodgett films (LBF), the method of Second Harmonic Generation (SHG) seems to be one of the most powerful ones. This method followed the discovery of SHG phenomenon in LBF [1]. So far, SHG was observed in LBF of various organic compounds. Recently, a few papers appeared dealing with studies of LBF surfaces by the SHG method (see, for example, [2]). It is characteristic that one can use this method to conclude about such properties of the films as degree of their homogeneity, orientation of the component molecules, etc. A strong dispersion-induced increase in the nonlinearities in combination with weak absorption in thin LBF can result in the generation of quite strong SH even if the molecules do not have the specific structural criteria [3] of high hiperpolarisability. Among such molecules, bacteriorhodopsin (bR, pygment of purple membranes of bacterium Halobacterium Halobium) is selected in this paper to demonstrate possibilities of the method.