Fig. 6

Removed gold volume as function of defocus. The largest volume (top) is calculated from the single largest continuous removed gold area, and the total volume (bottom) from the sum of all removed gold areas. For all frequencies, the volumes are normalized to their respective maximum. For all frequencies maximum removal is observed above the focus, around which removal tapers off. For 4.2 MHz significant removal in total volume is observed also at negative defocuses, owing to dispersed small removal spots. Asterisks (*) denote the selected optimal defocuses: +200 μm for 4.2 MHz and 11.8 MHz, and + 500 μm for 7.3 MHz. Lines are shown to guide the eye.