Pressure pulse methods can be used to determine the distribution of the charges in the thickness direction of dielectrics with µm resolution. One such method is the laser-induced pressure pulse method (LIPP method), which is illustrated in the left-hand part of Fig. 1 [1-3]. In this technique, a short laser pulse is absorbed at the sample surface. The heating of the surface layers generates a pressure pulse which propagates through the dielectric. Changes in geometry and permittivity caused by this pulse produce a current in the external circuit which is shown in the right-hand part of the Figure. The current at any instant is directly proportional to the charge density ρ(x), the polarization gradient dP/dx, and the gradient of the piezoelectric e-coefficient at the momentary location of the pressure pulse. The display at the oscilloscope shows therefore directly the distribution of these quantities as a function of location.
The LIPP method is widely used to determine charge and polarization distributions in polymers. An example of such a study is the measurement of the deposition-profile of monoenergetic electrons in Teflon, as shown in Fig. 2 . Measurements of this kind are important for basic investigations of charge storage and charge dynamics in dielectrics and have been used to test models of charge transport in polymers . The LIPP method is also employed for practical applications such as the exploration of charge penetration into cable insulation .
-  G. M. Sessler, J. E. West, and R. Gerhard, “Measurement of Charge Distribution in Polymer Electrets by a New Pressure-Pulse Method”, Polymer Bulletin 6, 109 – 111 (1981).
-  G. M. Sessler, J. E. West, and R. Gerhard, “High-Resolution Laser-Pulse Method for measuring charge distributions in dielectrics”, Phys. Rev. Lett. 48, 563 – 566 (1982).
-  G. M. Sessler, J. E. West, R. Gerhard-Multhaupt, and H. von Seggern, “Nondestructive Laser Method for Measuring Charge Profiles in Irradiated Polymer Films”, in IEEE Trans. Nucl. Sci. NS-29, 1644 – 1649 (1982).
-  G. M. Sessler, M. T. Figueiredo, and G. F. Leal Ferreira, “Models of charge transport in electron-beam irradiated insulators”, IEEE Trans. Diel. and Electrical Insulation, 11, 192-202 (2004).
-  G. M. Sessler, “Distribution and Transport of Charge in Polymers”, in Electrets, Vol. 2, 3rd Edition (R. Gerhard-Multhaupt, Ed., Laplacian Press, Morgan Hill, CA, 1999) Chapter 10, pp. 41 – 80.