<title>Accurate measurement of thin-polymeric-films index variations: application to elasto-optic effect and to photochromism</title>

Abstract

Attenuated Total Reflection (ATR) is commonly used for measuring small variations of the index of refraction of thin polymeric films. We show that a careful analysis of reflectivity dips, due to the exitation of guided modes in the film, allows a precise measurement of very small variations of the anisotropic index of refraction and of the thickness of the film. This is very useful for studying a wide variety of physical phenomena such as electro-optic effects, piezoelectricity, electrostriction, mechanical and thermal strains inducing elasto-optic effects (i.e.photoelasticity) and photochromism. In this paper we particularly emphasize the measurement of some components of the photoelastic tensor and of the index variations associated with cis-trans photoisomerization of azo dyes which have been clearly demonstrated in doped polymeric films. Kinetics of cis-trans optical pumping and of relaxation in darkness have been studied. It is noticeable that the layered configuration of samples and the guided waves excited by ATR are quite similar to the structure and to the propagation conditions of integrated optics devices.

Light-tunable Fano resonance in metal-dielectric multilayer structures

“…The close similarity allows us to attribute the present photoinduced shift of the Fano resonance to the photoisomerization of the DR1 molecules dispersed in the PMMA layer. As described in detail in our previous papers 35 36 39 40 , thermal effects can be ruled out as the origin of the observed shift.…”

“…The DR1 molecule is one of the azobenzene derivatives exhibiting trans - cis photoisomerization, and its trans form is known to be stable 33 34 35 36 37 38 . Both trans - and cis -DR1 molecules have absorption bands in the blue region of the spectrum, and they transform into each other by reversible photoisomerization as schematically shown in Fig.…”

“…Cis -DR1 molecules revert to trans -DR1 molecules by thermal relaxation as well. Optical phenomena related with the trans - cis photoisomerization of azobenzene derivatives have been investigated extensively over two decades 33 38 , in particular for DR1 molecules embedded in PMMA matrices 34 35 36 37 39 40 41 42 . Linear and nonlinear optical properties of the DR1-doped PMMA films are governed by the orientation of the trans molecules, because they have large transition dipole moments along the long molecular axis.…”

Light-Tunable Fano Resonance in Metal-Dielectric Multilayer Structures

“…The DR1 molecule is one of the azobenzene derivatives exhibiting trans-cis photoisomerization, and its trans form is known to be stable [33][34][35][36][37][38] . Both trans-and cis-DR1 molecules have absorption bands in the blue region of the spectrum, and they transform into each other by reversible photoisomerization as schematically shown in Fig.…”

“…Cis-DR1 molecules revert to trans-DR1 molecules by thermal relaxation as well. Optical phenomena related with the trans-cis photoisomerization of azobenzene derivatives have been investigated extensively over two decades 33,38 , in particular for DR1 molecules embedded in PMMA matrices [34][35][36][37][39][40][41][42] . Linear and nonlinear optical properties of the DR1-doped PMMA films are governed by the orientation of the trans molecules, because they have large transition dipole moments along the long molecular axis.…”