Ordinarily, plasma is dangerously hot; Ochiai’s tests with nanosecond blasts quickly incinerated bits of leather. But by shortening the bursts from nanoseconds to femtoseconds — quadrillionths of a second — Ochiai’s team can make the plasma safe for fingers. Although the ultrashort bursts do ionize the skin’s surface, turning it into plasma, it’s not long enough to cause damage. Instead, the ionization makes shock waves across the finger’s surface, resulting in a tingling sensation. Ochiai says it feels like touching sandpaper.
Contact with flesh also causes the plasma to brighten, an effect Ochiai plans to exploit for interactive holograms, noting that the brightening can provide a visual cue for video tracking.