[PDF]     http://dx.doi.org/10.3952/lithjphys.52103

Open access article / Atviros prieigos straipsnis

Lith. J. Phys. 52, 30–38 (2012)


EFFECTS OF THE MULTIPLE INTERNAL REFLECTION AND SAMPLE THICKNESS CHANGES ON DETERMINATION OF ELECTRO-OPTIC COEFFICIENT VALUES OF A POLYMER FILM
E. Nitissa, M. Rutkisa, and M. Svilansb
aInstitute of Solid State Physics, University of Latvia, Kengaraga 8, LV-1063 Riga, Latvia
bFaculty of Material Science and Applied Chemistry, Riga Technical University, Āzenes 14/24, LV-1048 Riga, Latvia
E-mail: edgars.nitiss@cfi.lu.lv

Received 8 September 2011; revised 18 January 2012; accepted 1 March 2012

New nonlinear optical (NLO) active organic materials are appealing candidates for optoelectronic and photonic technologies. For the evaluation of new NLO polymer materials for applicability in the mentioned technologies, the most important criteria are their electro-optic (EO) coefficients. We have implemented the Mach–Zehnder interferometric (MZI) method for the determination of EO coefficients of thin organic films. Despite the fact that other multiple optical methods for the determination of thin film EO coefficients are known, the MZI method has been chosen because this particular technique has high sensitivity to phase and intensity modulations in the sample arm of an interferometer and allows one to determine independently both thin film EO coefficients, r13 and r33. In addition to the drawbacks described earlier we demonstrate that some other effects like electrostriction and multiple internal reflections in the sample have a considerable influence on light intensity at the MZI output. Taking into account these effects we have performed numerical simulations of the EO effect caused MZI output changes or modulation depth at different incidence angles using the Abeles matrix formalism. We can show that the modulated signal at the MZI output is highly dependent on the sample structure and is mainly governed by the effects mentioned above. For analysis of modulated signal components and determination of EO coefficients of a thin polymer film, a series of experiments was carried out on PMMA + DMABI 10 wt% samples.
Keywords: electro-optic coefficient, Mach–Zehnder interferometric method, nonlinear optical polymer, multiple internal reflections in polymer films
PACS: 81.70.Fy, 82.35.Ej
DAUGKARTINIO VIDINIO ATSPINDŽIO IR BANDINIO STORIO KITIMO ĮTAKA POLIMERINIO SLUOKSNIO ELEKTROOPTINIŲ KOEFICIENTŲ VERČIŲ NUSTATYMUI
E. Nitissa, M. Rutkisa, M. Svilansb
aLatvijos universiteto Kietojo kūno fizikos institutas, Ryga, Latvija
bRygos technikos universiteto Medžiagotyros ir taikomosios chemijos fakultetas, Ryga, Latvija

Naujos organinės netiesiškai optiškai aktyvios medžiagos yra naudojamos optoelektroniniuose ir fotoniniuose taikymuose. Tokių medžiagų tinkamumas minėtiems taikymams gali būti vertinamas pagal jų elektrooptinius (EO) koeficientus. Mes pritaikėme Macho ir Cėnderio (Mach–Zehnder, MZ) interferometrijos metodą plonų organinių sluoksnių EO koeficientams nustatyti. Nepaisant daugybės kitų EO koeficientų nustatymo ploniems sluoksniams optinių metodų, šį metodą pasirinkome todėl, kad jis pasižymi dideliu jautrumu fazės ir intensyvumo moduliacijoms interferometro bandinio petyje ir leidžia nepriklausomai matuoti abu plonojo sluoksnio EO koeficientus – r13 ir r33. Parodėme, kad elektrostrikcija ir daugkartiniai vidiniai atspindžiai bandinyje stipriai veikia šviesos intensyvumą MZ interferometro išėjime. Atsižvelgdami į šiuos reiškinius, skaitmeniškai naudodami Abelès matricų formalizmą, sumodeliavome EO koeficientų poveikį MZ interferometro signalo kaitai arba moduliacijos gylį esant skirtingiems kritimo kampams. Pavyko parodyti, kad moduliuotas signalas MZ interferometro išėjime labai priklauso nuo bandinio sandaros ir yra stipriai lemiamas EO koeficientų. Moduliuoto signalo sandų analizei ir plonų polimerinių sluoksnių EO koeficientų nustatymui atlikome keliolika eksperimentų su PMMA ir 10 svorio % DMABI bandiniais.


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