A scanning laser Doppler vibrometer is used to make quantitative measurements of 2D ultrasound fields in air. The laser light traverses the measurement volume to and from a rigid reflector and determines the velocity of the change in optical path length, which with constant geometry only depends on the changes in index of refraction. Assuming adiabatic conditions, the refractive index rate is proportional to the sound pressure rate and quantitative measures of the sound field are possible to achieve. The emitted or scattered ultrasound being measured origins from a source or object outside the recording area. Using phase conjugation the sound field is then digitally reconstructed outside the recording area, and the reconstructed phase and intensity reveals the location of the source or object. The combination of several such reconstructions of ultrasound fields of different wavelengths, so called wavelength scanning, provides an intensity map that very accurately gives the position of the source. This opens many new possibilities to study hidden or unknown sound sources or scattering objects.

Date Published: 30 May 2003
PDF: 11 pages
Proc. SPIE 5144, Optical Measurement Systems for Industrial Inspection III, (30 May 2003); doi: 10.1117/12.500398

Published in SPIE Proceedings Vol. 5144:
Optical Measurement Systems for Industrial Inspection III
Wolfgang Osten; Malgorzata Kujawinska; Katherine Creath, Editor(s)