The influence of a ferroelectric domain wall on the fabrication of a pyroelectric laser energymeter

Abstract

A region across a ferroelectric domain wall has been scanned, using an Nd:YAG laser beam (beam size 440 µm), in a thin crystal of TGS (triglycine sulphate), cut normal to the polar axis and the pyroelectric response of the crystal has been recorded. If a laser pulse of fixed beam size falls on the domain completely, then the output pyroelectric signal is maximum. But when the laser beam (diameter of beam greater than width of domain wall) falls on the domain wall, the pyroelectric signals from two opposite domains tries to cancel each other and net signal depends on the position of laser beam across the domain wall. When the domain wall lies in the middle of the laser beam the output pyroelctric signal will be zero. In our experiment when beam of size 440 µm falls on positive domain the pyroelectric voltage of -2.76 mV recorded and when beam starts crossing the domain wall (i.e from positive domain to negative domain), the pyoelectric signal changes its sign from negative to positive through zero. After 220 µm the signal decreased to minimum and again increases to maximum (+2.46 mV) in opposite direction after 440 µm i.e when beam falls on the negative domain completely. This shows that the polarization in the domain wall region (separating two domains) is zero i.e the paraelectric nature of domain wall. So before detector fabrication the sample must be poled sufficiently to avoid the non uniformity of pyroelectric signal due to the domain wall.