Nowadays, it seems evident that a unique nonlinear optical (NLO)material cannot offer simultaneously linear transparency,colour neutrality and broadband optical limiting efficiency at the performance levels required for sensor and eye protection against all laser threats.Several combinations of NLO materials were investigated last few years, including multicell or multilayer geometries.
The approach presented here combines multiphoton absorption with nonlinear scattering. For that purpose, singlewall carbon nanotubes are suspended in various solutions of multiphoton absorbing chromophores. Such combinations allow us to obtain optical limiters of high linear transmittance and excellent colour neutrality. Broadband optical limiting is expected from the association of these two broadband materials,and enhanced optical limiting efficiency is expected from cumulative effects in the nanosecond regime.
We report here on the optical limiting studies performed with nanosecond laser pulses on several families of multiphoton absorbers in chloroform,with carbon nanotubes suspended in the solutions. The performances of these samples are compared with those of simple multiphoton absorber solutions and carbon nanotube suspensions, and the differences observed are interpreted in terms of cumulative NLO effects and adverse aggregation phenomenon. Ways to optimise stability of the suspensions are also experimented and discussed.
The sol-gel synthesis of organic-inorganic composite materials with push pull azobenzene molecules covalently bonded to the silica matrix is used for fabricating low cost optical channel waveguides for integrated optics applications and optical information storage. The refractive index change is obtained through the orientation of the nonlinear active molecules induced by a trans-cis-trans photoisomerization process. The index change and anisotropy are created by illuminating the thin film at a wavelength located inside the absorption band of the chromophores. At short irradiation times, the induced birefringence and dichroism are the consequence of the usual reorientation phenomenon due to the trans-cis-trans isomerization. At long pumping times, a photobleaching is observed corresponding to an irreversible transformation in the silica matrix. This property is used to write channel waveguides and gratings.