Fairy Lights: A safe-to-touch 3D midair display that uses femtosecond lasers to create holograms

Fairy Lights, A safe to Touch 3D Midair Display-1

From Star Wars to Iron Man, holograms have, until now, remained firmly confined within the world of pop-cultural science fiction. For those who are not aware, hologram is a sort of three-dimensional projection of an image, be it a person or an object, formed as a result of the interference of coherent beams of radiation from a laser or some other light source. Of the few, currently-available holographic technologies, majority rely on optical tricks and illusions of some form or the other. Interestingly, while 3D laser-induced midair displays do exist at present, the combination of lasers and plasma make these contraptions somewhat dangerous to use. Recently, a group of Japanese researchers has come up with an ingenious solution, which involves increasing the speed of the lasers to create an innovative, safe-to-touch laser plasma display. 

Central to the research is the fact that plasma produced by a femtosecond laser is far safer than than kind generated by a nanosecond laser. As one can see in the following video, of a 3D midair display developed by Japan-based company Aerial Burton, existing technologies create bright three-dimensional pixels, known as volumetric pixels or voxels. The particles are in fact air molecules, ionized with the help of an infrared laser. Subsequently, the volume pixels release their extra energy in the form of glimmering, bluish-white photons.

However, the plasma is extremely short-lived, which means that for such a display to be actually visible and tangible, one needs to use a laser that can swiftly scan through a given volume of air, emitting several hundred thousand optical pulses per second. This in turn creates a series of bright, yet brief, voxels that together form the effect of a moving, three-dimensional image. Unfortunately, nanosecond laser-induced plasma usually contains a large amount of energy, enough to actually burn human skin.

Luckily, scientists, from Japan’s University of Tsukuba, Nagoya Institute of Technology, University of Tokyo and the Utsunomiya University, have devised a solution, in the form of the advanced “Fairy Lights” system. Based on ultrafast femtosecond lasers, the technology is believed to be completely safe to touch. By effectively increasing the speed of the laser to the scale of femtoseconds – one quadrillionth of a second – the team has successfully developed a three-dimensional midair display that is surprisingly tangible. Speaking about the project, the researchers said:

Our system has the unique characteristic that the plasma is touchable. It was found that the contact between plasma and a finger causes a brighter light. This effect can be used as a cue of the contact. One possible control is touch interaction in which floating images change when touched by a user. The other is damage reduction. For safety, the plasma voxels are shut off within a single frame (17 ms = 1/60 s) when users touch the voxels. This is sufficiently less than the harmful exposure time (2,000 ms).

Fairy Lights, A Safe to Touch 3D Midair Display-2

According to the team, pulse duration, of a femtosecond laser, is too small to cause any significant skin damage, unless of course it is fired at the same spot for over 2,000 milliseconds. This makes the plasma, and in turn the display, completely safe to touch. The scientists elaborated:

Shock waves are generated by plasma when a user touches the plasma voxels. The user feels an impulse on the finger as if the light has physical substance. The detailed investigation of the characteristics of this plasma-generated haptic sensation with sophisticated spatiotemporal control is beyond the scope of this paper.

Currently, the technology is available only for extremely tiny displays, measuring only about eight cubic millimeters in area. By contrast, the spatiotemporal resolution of the display is high, at around 200,000 voxels every second. However for it to be commercialized, the “Fairy Lights” display system needs to be scaled up, which the researchers believe, is possible with the help of a variety of different optical devices.

Fairy Lights, A safe to Touch 3D Midair Display-1

Via: IEEE Spectrum

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