Using
femtosecond lasers (a femtosecond is a quadrillionth of a second, and the
lasers transmit bursts that last 30 to 270 femtoseconds), the team can make
holograms that are safe to touch. The images are three-dimensional, with
resolutions up to 200,000 dots per second. The voxels are light emitted by
plasma that's created when the laser's focused energy ionizes the air. When
touched, the laser feels like sandpaper, although some participants thought the
plasma felt a little like a static shock. This isn't the first attempt at using
femtosecond lasers to form air plasma researchers state at the University of
Rochester, but the study should help in designing future femtosecond laser
displays. Although previous studies have used nanosecond and femtosecond lasers
to create images, the DNG researchers say preceding studies haven't achieved
resolution this high, and would burn human skin.
Since the lasers
fire at such a high speeds, they're able to react in realtime, and researchers
have demonstrated its ability to make usable holographic checkboxes and hearts
that break when touched. To create their hologram, researchers fired their
femtosecond laser through a spatial light modulator, which positions a mirror
to precisely direct the laser beams. A camera underneath the hologram captures
user interaction, allowing the dots to respond to being touched. Researchers
say the most surprising thing he realized was that plasma was actually safe to
touch in this application, making the hologram exponentially safer than
previously thought. The key to making these holograms safe is the shorter
duration of the laser’s bursts. In tests, if the lasers fired in more than two
second bursts, they burnt the leather researchers used to simulate skin.
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