Parametric Optical Interactions in Bacteriorhodopsin Films
Résumé
Chiral materials with non linear optical properties can be found also among biological molecules presenting an ordered arrangement and non-inversion-symmetric structure in space, or having a chromophore. The latter group, called chromoproteins, is best represented by bacteriorhodopsin (BR), one of the most studied biomolecules exhibiting NLO properties [1]. We have studied BR in its purple membrane bound form by producing a 15  thick oriented film via electrophoretic deposition onto a glass substrate covered by a 60nm thick ITO film. The resulting BR films, composed by ~2600 purple membrane layers (of 5nm thickness each) were characterized in terms of homogeneity, optical and electrical properties. In order to study the coherence optical response of BR we performed parametric nonlinear interaction (second harmonic generation (SHG) measurements) in noncollinear configuration. The noncollinear scheme with two input pump beams, offer very high flexibility in the handling and control the SHG signal which becomes selectively addressed by choosing the appropriate polarization state for the fundamental beams [2].The noncollinear second harmonic generation from the BR film was obtained using the output of a mode-locked femtosecond Ti:Sapphire laser system tuned at ï¬=830 nm (76 MHz repetition rate, 130 fs pulse width, average power of 500 mW) which was split into two beams of about the same intensity. The coherence of the interaction can be handled by an additional input beam in the absorption regime. The presence of the nonlinear magnetization and its contribution to the SHG signal, can be also tuned and modulated by the application of an external static magnetic field of moderate intensity. References [1] F.A.Bovino, MC Larciprete, C Sibilia, G.Varo, C.Gergely ,Optics Express, 20,14621 (2012) [2] M.C Larciprete, F A Bovino, M Giardina, A Belardini, M Centini, C Sibilia, M Bertolotti, A Passaseo, V Tasco, Optics Letters 34: 2189 (2009)