THERMAL WAVE PROBING OF PYROELECTRIC DISTRIBUTIONS IN THE SURFACE REGION OF FERROELECTRIC MATERIALS - A NEW METHOD FOR THE ANALYSIS

For the investigation of polarization distributions in pyroelectric materials, the laser intensity modulation method (LIMM), which is based on thermal waves, is widely used. With this method, the sample under investigation is heated by the absorption of intensity modulated light at one surface, while the pyroelectric current is measured. The thermal excitation generates a thermal wave penetrating into the sample. The penetration depth is varied with the modulation frequency. A new procedure for the reconstruction of the polarization distribution from a measured pyroelectric current spectrum is introduced. This procedure is especially well suited for polarization probing near the sample surface. An approximation for the polarization distribution is calculated from a measured pyroelectric spectrum in a very simple and direct way, avoiding mathematical instabilities. The calculation can be performed during the measurement of a pyroelectric current spectrum. This makes LIMM an on-line procedure. The new technique of analysis is applied to the measurement of thin depolarized layers near the surface of homogeneously poled ferroelectric polymer films.