Second-harmonic generation studies in the B-2 and B-4 phases of a banana-shaped liquid crystal - art. no. 011702

Second-harmonic generation (SHG) measurements have been performed in the B- 2 phase of the achiral banana-shaped molecule with n = 12 alkoxy end chains (P-12-O-PIMB). A quantitative value of the nonlinear efficiency has bct n obtained from SHG curves at oblique incidences, taking into account that th e signal is generated by a random orientation of different domains. In the B-4 phase, circular dichroism, optical absorption and SHG studies have been carried out. It has been found that there are no simple helical arrangemen ts giving rise to selective reflection in the visible region of the spectru m. In addition, some unusual features of the SHG behavior ore pointed out, It is concluded that the phase is intrinsically inactive for the SHG proces s. The detected signal is due to the presence of some birefringent inclusio ns that are created at the B-2 to B-4 transition and slowly disappear while the sample is maintained within the B-4 phase. A structural model fur thes e inclusions is presented.