Ferroelectric liquid-crystalline polymers for photoinduced switching of nonlinear optical response

Organic materials are expected to provide an inexpensive and easily processable alternative to inorganic crystals, which are currently used as high-performance nonlinear optical (NLO) materials [1]. In addition to strong and ultrafast NLO response, some organic molecules possess an advantage that the response can be switched “on” and “off by external means. However, turning the molecular level changes into bulk-level switching in a solid material remains a challenge, particularly for the second-order NLO response. This is due to the requirement of noncentrosymmetry, both on the molecular and macroscopic levels, for any second-order NLO process. Earlier attempts to reach switchable second-order NLO response have relied on modifying the molecular hyperpolarizability while avoiding changes in the molecular alignment [2-4]. The modulation values have been <;50% and most of the material systems suffer from gradual irreversible changes in the molecular order. Here, we present an alternative route to photoswitchable second-order NLO response, which relies on reversible molecular-alignment control without modification of the molecular hyperpolarizability [5].