Two studies (Kiessling et al., 2015 and Schlaudraff et al., 2014) have shown pictures of cavitation bubbles from radial shockwave heads from a 6mm head (Kiessling et al., 2015) and a 36mm head (Schlaudraff et al., 2014).
Both took the images in a similar but not identical way:
Kiessling et al. (2015)
"High-speed imaging of cavitation bubbles. These investigations were performed at the Hydraulic Machines Laboratory of the E´cole Polytechnique Fe´de´rale de Lausanne (Lausanne, Switzerland). The tip of the 6mm applicator of the Swiss DolorClast, mounted on the ‘‘radial’’ handpiece, was submerged in de-ionized water contained within a custom-built transparent cubic vessel made of clear high-density polycarbonate (20cm side length, 1cm wall thickness). TheDolorClast was operated at 4.0 bar and 5 Hz. Measurements were run in triplicates. For documentation of cavitation bubble dynamics, a high-speed CCD camera (Photron Ultima APX; Photron, Tokyo, Japan) with a framing rate of 300,000 frames per second and exposure time of 1/2,700,000 seconds was used. Each captured frame comprised a total of 8192 (64 3 128) pixels, encompassing an area of approximately 8.8 3 17.6 mm. Transmitted light illumination was provided by a high-power light source (Cordin Light Source Model 359; Cordin, Salt Lake City, UT, USA). Gas bubbles appeared dark in this setup due to their light scattering properties. The applicator was lowered from above into the camera frame’s top section. Camera recordings were triggered manually prior to the release of a single pulse. Individual film sequences (approximately 10,000 continuous frames, equivalent to film duration of 33 ms) were subsequently visualized using FASTCAM viewer software (Photron, Tokyo, Japan), converted into individual images with 256 greyscales (with zero and 256 representing black and white, respectively), and exported as TIF files."
Schlaudraff et al., (2014)
"The images shown were taken approximately 1.5 mseconds before the cavitation maximum, and images approximately 1.5 mseconds after the cavitation maximum. Cavitation lasted for approximately one mseconds. The pictures were taken with a high-speed CCD camera (Photron Ultima APX; Photron, Tokyo, Japan) with a framing rate of 300,000 frames per second and an exposure time of 1/2,700,000 seconds. Note that the cavitation field (and thus the pressure field below the applicator) is broader when generating radial shock waves at 15 Hz than at 1 Hz. This phenomenon is observed for many radial shock wave devices."