Attenuated Total Reflectance

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Overview

Attenuated Total Reflection or ATR is a technique used together with Teng Mann to measure the R33 of electro-optic materials. A beam of IR light is directed through a prism at an angle exceeding the critical angle for internal reflection. This produces an evanescent wave at the prism surface. If a EO polymer is pressed in intimate contact with the prism they can be coupled so that he evanescent wave stimulates emission from the sample. This emission is measured with a photodiode. An electric field applied to an EO polymer changes its index of refraction which alters the critical angle.

Technique

Part 1 Sample Setup and calibration

Part 2 Measurement and analysis

Significance

The electro-optic coefficient for a poled polymer film can be calculated as follows[1]

<math>r_{33} = \frac {2d\Delta R} {n^3_{TM} V_m} \frac {\delta n_{eff}} {\delta \theta} \left /( \frac {\delta R \delta n_{eff} } {\delta \theta \delta n_{TM} } \right ) \,\!</math>

where

<math>R\,\!</math> is the DC reflected signal
<math>V_m\,\!</math> is the AC modulation voltage
<math>n_{eff}\,\!</math> is the ordinary index of refraction
<math>n_{TM}\,\!</math> is the film refractive index

References

  1. J. Phys. Chem. C, 2008, 112 (21), pp 7983–7988 DOI: 10.1021/jp712154g.
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