Schematic diagram of focusing system, showing the characteristic angle of the axicon, , and the focal length of the converging lens. The resulting radius of the ring can be calculated using Eq. (1).
A schematic diagram of the experimental arrangement (not to scale) showing the paths of the infrared and the green beams. AX indicates an axicon, BS a beam splitter, M a mirror, and a lens. The ratio of focal lengths and indicate the optical magnification for interferometry (CCD1) and schlieren imaging (CCD2).
(a) Power density as a function of ring radius for the high-power density laser. The insert shows an image of the ring obtained by focusing a low-power cw laser. (b) Optical scanned image of the erosion produced in a bronze target using the high-power laser along with a line out showing its radial profile.
Series of schlieren images for (power density of ) and (power density of ) obtained from different shots. Both series were taken at of hydrogen. The times stated correspond to the delay between the arrival of the IR beam and the image.
Definition of the and directions, parallel and perpendicular to the surface.
Calculated propagation velocity from schlieren images.
Interferograms at , 75, and for the case of , with a power density of .
Measured electron and neutral gas density profiles for , 75, and , , case. is the background gas density.
(a) Side-on, filtered, time-integrated image of the annular plasma with , and a power density of (b) Schematic representation indicating three zones: 1—hydrogen plasma expansion, 2—titanium ring plasma, and 3—initial ring plasma.
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