Laser-intensity-modulation method: A technique for determination of spatial distributions of polarization and space charge in polymer electrets

A new method for measuring the spatial distribution of combined polarization and space charges in poled polymer electrets has been developed. The technique, called the laser-intensity-modulation method (LIMM), is based upon measurement of the pyroelectric current generated by the electret when it is heated with a laser beam which is intensity-modulated at frequencies varying from 200 to 2500 Hz. A special analytical technique is used to transform the current-frequency measurements to spatial distributions. The method gives high resolution and is very stable with respect to measurement errors. The technique can be easily implemented in a laboratory with conventional equipment. The advantages and limitations of LIMM are illustrated by means of calculations based upon simulated data. Experimental results on a number of laboratory and commercially poled samples are presented.