E. Meyer 155 
Fig. 9.26. Luminescence pulses and 
shock waves. 
lapses. In the last stages of the collapse, the cavity disintegrates into a great 
number of smaller cavities, and therefore a large number of light pulses is also 
observed. Luminescence requires the presence of small quantities of gas which 
are excited to emit light. If the initial pressure in the glass spheres exceeds 
about 20 torrs, the luminescence almost entirely disappears; the luminescence 
pulses are very small for water with small gas contents, but relatively large 
for glycerin with krypton as the gas and higher gas contents, 
Another interesting effect is the sonoluminescence occurring together with 
ultrasonic cavitation. Such experiments were made by Meyer and Kuttruff [18], 
and Fig. 9.24 shows instantaneous photographs of cavitation bubbles. The. photo- 
graphs were made at 30° intervals of the phase of the vibration of the exciting 
system which was a nickel rod vibrating at 2.4 kcps. Phase zero indicates 
shock waves distance 
ts) 
Luminescence pulses and shock waves 
0 5 10 15 Gus} 
Fig. 9.27. Time delay between spark illumination and luminescence pulse. 
