Laser-induced dielectric breakdown as a method for noncontact pressure measurement.

Abstract

Being able to accurately measure pressure fields in acoustic experimentation is of critical importance for understanding and describing observed acoustical phenomena. However, in many experimental situations, it is undesirable or impossible to measure the acoustic field using a transducer in contact with the acoustic host medium. It becomes useful then to have alternative, noncontact, methods for reliably and accurately measuring pressure fields in experiments. One alternative to traditionally invasive means, such as the use of a hydrophone, to measure pressure, is to use focused, short (5–7 ns), high power laser pulses to cause dielectric breakdown. Breakdown events can be detected by looking for the signature, near instantaneous, flash of broadband light generated by the subsequent ionization cascade. This procedure can then be repeated under different known hydrostatic pressures to establish pressure’s effect on the breakdown strength of water. Once a relationship is established, the process can be used to map local pressures in acoustic fields of sufficiently long period as to be considered hydrostatic in relation to the laser pulse duration. [Work supported by the US Army Space and Missile Command.]