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Acta Optica Sinica

Optical phase conjugate in Langmuir-Blodgett films of purple membrane

Qingguo Li

Published Jan 1, 1993• 0 citations
OpenAlex

Abstract

We report an observation of optical phase conjugate in LB films of pure purple membrane for the first time. The dependence of intensity of the optical conjugate wave upon the total incident intensity has been deduced, based on the simplified model of photo-cycle of bacteriorhodipsin [bR (570) M(410)]. The fitting restults of the saturated absorption intensity of the LB films and the life time of the intermediate M (410) are 0. 49 W/cm2and 2. 5 ms, respectively.

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We report an observation of optical phase conjugate in LB films of pure purple membrane for the first time. The dependence of intensity of the optical conjugate wave upon the total incident intensity has been deduced, based on the simplified model of
photo-cycle of bacteriorhodipsin [bR (570) M(410)]. The fitting restults of the saturated absorption intensity of the LB films and the life time of the intermediate M (410) are 0. 49 W/cm2and 2. 5 ms, respectively.
Saturating absorption and optical bistability (OB) with ns switching time in Langmuir-Blodgett (LB) films of phthalocyanines derivatives on reflection have been studied at room temperature (RT) in the near ultraviolet region for the first time. The saturating intensity (Is) and switching intensity for the OB at 337.1 nm are about 1 MW/cm2 and 5 MW/cm2, respectively. The experimental results show that the major nonlinear and positive feedback mechanisms for the OB are the change of refractive index caused by the saturating absorption and the simple F-P cavity due to the natural faces of the sample, respectively.
Optical Phase-Conjugation (OPC) has been observed in Methyl Green (MG) dye sensitized gelatin films in Degenerate Four-Wave Mixing (DFWM) configuration at 633 nm radiation from a He-Ne laser of total power 35 mW.The mechanism of Phase-Conjugate (PC) wave generation associated with this dye-doped system was discussed.The dependence of the PC wave generation on the incident angle between the forward-pump and the probe beams and time of evolution were also studied.A maximum phase-conjugate beam reflectivity of about 0.13% has been observed in this dye-doped gelatin films.
Studies on low power optical phase conjugation (OPC) in three saturable dyes, viz., eosin, erythrosin B, and rose bengal, embedded in two polymer films, viz., gelatin and polyvinyl alcohol, are presented. Experiments are performed using the 514.5 nm line of an argon-ion laser. Saturation intensities are determined from the transmission versus intensity plots, and triplet lifetimes are estimated from the phosphorescence decay curves. OPC experiments are performed, and the variation of OPC reflectivity with intensity and absorption length is studied. Experimental results are compared with the theory of degenerate four-wave mixing in absorbing media proposed by R. L. Abrams and R. C. Lind [Opt. Lett. 2(4), 94 (1 978)]. There is fair agreement between the theory and the experimental observations. The limitations in using these films for cw OPC applications are briefly discussed.
Phase conjugation by degenerate four-wave mixing in a saturable absorbing medium with a relatively long-lived excited state is analyzed; the analytical results are compared with experimental results. We propose a four-level model and take into account the effects of both excited-state absorption and pump propagation to explain the experimental results, which could not be explained by the models proposed previously. The numerical result predicts that the value of the phase-conjugate reflectivity as a function of the pump intensity is maximum at a certain absorbance (as absorbance increases) that is dependent on the cross section of the excited-state absorption. The present analysis explains most observations in the experiment, which was performed with a saturable-dye-doped polymer film as the saturable absorbing medium.
A spatio-temporal analysis of non-degenerate two-wave mixing in a saturable absorber, such as bacteriorhodopsin (bR) film, is performed. To do this, a theoretical model describing the temporal variation of the intensities is developed by taking into account the dielectric constant as a function of bR population. A good agreement between theory and experimental measurements is obtained. Thus, the dependence of the optical gain and the main dielectric constant parameters are studied at different intensities and frequencies. As a result, the best intensity-frequency zones where higher coupling is reached are proposed, and it is also demonstrated that non-uniform patterns, which evolve over time as a function of frequency difference, can be observed.
We report direct observations of all-optical mirrorless bistability associated with saturable absorption in three kinds of bacteriorhodopsin (BR) samples: wild-type BR in water solution and dispersed in thin films of a polymer matrix as well as water solution of the genetically engineered mutant BRD96N. The experiments are carried out with picosecond pulses at 532 nm. The values measured for the saturation intensity are explained in terms of the relaxation of the excited M state population to the B state of the BR photocycle for the three kinds of samples studied.