SINGLE-SHOT SPATIALLY-RESOLVED CHARACTERIZATION OF LASER-INDUCED SHOCK-WAVES IN WATER

We have developed an optical method for single-shot spatially resolved shock-wave peak-pressure measurements. A schlieren technique and stre ak photography were used to follow the propagation of the shock wave. The shock position r as a function of time was extracted from the stre ak images by digital image-processing techniques. The resulting r(t) c urves were differentiated with respect to time to yield shock-wave vel ocities that were converted to shock pressures with the aid of the equ ation of the state of the medium. Features and limitations of the tech nique are demonstrated and discussed on the basis of measurements of s hock-wave amplitudes generated by laser-induced breakdown in water. Fo r this purpose, laser pulses of 6-ns duration and pulse energies of 1 and 10 mJ were focused into a cuvette containing water. Complete p(t) curves were obtained with a temporal resolution in the subnanosecond r ange. The total acquisition and processing time for a single event is similar to 2 min. The shock-peak. pressures at the source were found t o be 8.4 +/- 1.5 and 11.8 +/- 1.6 GPa for pulse energies of 1 and 10 m J, respectively. Within the first two source radii, the shock-wave pre ssure p(r) was found to decay on average in proportion to r(-1.3+/-0.2 ) for both pulse energies. Thereafter the pressure dropped in proporti on to r(-2.2+/-0.1). In water the method can be used to measure shock- wave amplitudes exceeding 0.1 GPa. Because it is a single-shot techniq ue, the method is especially suited for investigating events with larg e statistical variations. (C) 1998 Optical Society of America.