SAN FRANCISCO, California (Reuters) --In a museum in Tampere, Finland, Ismo Rakkolainen's fog machine conjures up the Mona Lisa on an invisible sheet of water particles.

Thousands of miles away in Hermosa Beach, California, a graduate student passes his hand through an image of a DNA strand produced -- apparently out of thin air -- by a modified video projector.

The two inventions represent the latest front in advanced computer displays -- eliminating the screen altogether.

While unlikely to replace the desktop computer monitor, so-called walk-through displays could eventually be put to use in product showrooms, museums, and military training facilities.

"This is something that people have been dreaming about for a long time," said Chad Dyner, 29, a graduate student at the Massachusetts Institute of Technology and inventor of Heliodisplay, one of the prototype display systems. "Ever since the movie 'Star Wars' came out and there was a distress call from Princess Leia," -- generated in thin air by the robot R2D2 -- "people all over the world have been wanting one of these."[...]