Tuesday, July 28, 2015

Touchable Holograms


Touchable Holograms
Multiple Responses:
It seems that there are touchable holograms in every science fiction story, but now they have become reality in a lab in Japan. While our own force-field operated Star Trek-style holodeck might be far away, what we have is not any less impressive.

At Digital Nature Group they used a type of laser, called the femtosecond laser, to accomplish the feeling that you’re touching something while touching a hologram.

While this kind of laser has been used before in aerial plasma 3D graphics demonstrations, now it is safe for the human touch for the first time. This has been accomplished by reducing the duration of laser bursts, which are now higher resolution femtoseconds, and previously they have been in lower resolution femtoseconds and nanoseconds.

The team has filmed a demonstration video, and in it you can see a finger touching the holograms with no harm whatsoever. The holograms are made of voxels, which are little points of light that plasma emits when the laser focus ionizes the air. Some of the holograms we have seen include a little heart, a star, and a fairy as well – they are mere 3D representations of 2D images, but this technology could also be used for more complicated things as well.

The research team stated they would look forward to seeing their invention used for aerial holographic interfaces (sadly, no holodeck for now!), and the public will have the opportunity to view their femtosecond laser-based volumetric displays in August on the Siggraph 2015 exhibition.

Researchers in Japan have created a floating 3D holographic plasma display... with haptic feedback. The system, which is being presented at SIGGRAPH 2015 next month, can render up to 200,000 voxels per second, but the physical size of the display is just 1 cubic centimetre.

The system works by way of using a femtosecond laser to turn small pockets of air (voxels) into plasma. A femtosecond laser is a laser that fires for an incredibly short period of time—on the order of one quadrillionth of a second (or one millionth of one billionth of a second, if you prefer). The laser hits an atom or molecule, causing an electron to become ionised (move to a higher energy level). Shortly after, the electron loses its extra energy in the form of a photon that is emitted as visible light.

To go from a single plasma dot to a 3D display, the researchers passed the laser through a spatial light modulator (SLM) connected to a PC to create the hologram, and then a galvano scanner and varifocal lens to "draw" each voxel with specific X, Y, and Z coordinates.

One of the more intriguing aspects of the 3D display is that it also incorporates haptic feedback. According to the research paper, when you touch one of the voxels, "shock waves are generated by plasma ... the user feels an impulse on the finger as if the light has physical substance." The researchers don't go into any further detail on the topic, however.

The paper (freely available on arXiv) also notes that using a femtosecond laser (as opposed to a picosecond or nanosecond laser) is one of the more novel aspects of the system. Because the laser bursts are so short, the plasma isn't that energetic, and so it's safe to touch. The researchers also tested a nanosecond laser, but found that it burned a piece of leather within 100 milliseconds. The femtosecond laser setup appears to be safe and doesn't cause any skin damage when a user touches the display, though you still shouldn't look into the laser source.

For now, the holographic plasma display is too small to be of much use—and perhaps more importantly, the equipment used to produce the display is too large and expensive for anything outside of the lab. The principles are all quite sound, though, and there's a lot of interest in free-space display technologies that don't require some kind of screen or other medium to project the image onto.

The 3D holograms you can TOUCH: High-speed lasers create images that respond to strokes without burning the skin
  • Researchers used femtosecond lasers to create the safe 3D holograms
  • A femtosecond is a quadrillionth of a second and these lasers pulse with bursts that last between 30 and 270 femtoseconds
  • These pulses ionise the air to create plasma which can be touched
  • Previous research using nanosecond lasers damaged the skin

From Princess Leia in Star Wars to a holographic Tupac at the 2013 Coachella festival, holograms have fascinated scientists for decades.

But because they use lasers to project the hologram, it makes interacting with the images potentially dangerous - until now.

Researchers have created 3D holograms using lasers that fire at a quadrillionth a second, and they respond to touch without burning the user's skin.

The breakthrough was made by Japanese researchers from the University of Tokyo, University of Tsukuba, Utsunomiya University Nagoya Institute of Technology.

Holography uses lasers to record the brightness, contrast and dimensions of an image and project this image, typically in 3D, which can be viewed without specialist glasses.

When pixels are beamed and visible in 3D space they're known as voxels and are created when the energy from the laser ionises the air and releases extra energy in the form of photons which glow purple and blue.

Researchers and companies have used this technology to create plasma displays in the past, but these involved lasers that pulse with bursts that last for nanoseconds, for example.

Although this is a relatively short period of time, it is long enough for the bursts to be able to damage the skin or the surface of a material if touched.

To solve this problem the Japanese researchers created plasma voxels using femtosecond lasers instead.

A femtosecond is a quadrillionth of a second and these lasers pulse with bursts that last between 30 and 270 femtoseconds at a time.

The researchers fired the femtosecond laser through what's known as a spatial light modulator and a series of lenses into a Galvano scanner.

This scanner positions the beam through two more lenses onto a mirror to finally show the final voxel shape, dubbed Fairy Lights.  

A camera under the hologram is then able to capture and record a user's interactions, allowing the voxels to be 'touched.'

In reality, when a person touches the voxels the finger generates a shockwave, which the user feels as an pulse.

And because of the high-speed nature of the femtoseconds, the voxels are able to respond in real-time to these touches.

In a video revealing the technology, the touches are shown being used to tick a virtual checkbox, to change the word 'hate' to 'love' and to switch between an image of a heart and a broken heart.

An illustration in the research paper, called Fairy Lights in Femtoseconds: Aerial and Volumetric Graphics Rendered by Focused Femtosecond Laser Combined with Computational Holographic Fields, additionally shows it being wrapped around objects and used to create a virtual plant.

'We present a method of rendering aerial and volumetric graphics using femtosecond lasers,' explained the team.  

'A high-intensity laser excites a physical matter to emit light at an arbitrary 3D position.

'Popular applications can then be explored especially since plasma induced by a femtosecond laser is safer than that generated by a nanosecond laser.'

The holograms and workspace of the system are up to 1cm3 in volume but the researchers said they could be scaled up depending on what the technology is needed for.

Science fiction has promised us three-dimensional midair displays since at least the first Star Wars movie. We’ve seen a few holographic technologies that have come close; they rely on optical tricks of one sort or another to make it seem like you’re seeing an image hovering in front of you.

There’s nothing wrong with such optical tricks (if you can get them to work), but the fantasy is to have true midair pixels that present no concerns about things like viewing angles. This technology does exist, and has for a while, in the form of laser-induced plasma displays that ionize air molecules to create glowing points of light. If lasers and plasma sound like a dangerous way to make a display, that's because it is. But Japanese researchers have upped the speed of their lasers to create a laser plasma display that’s touchably safe .

Those brightly glowing voxels (pixels in three dimensional space) are air molecules that have been ionized at the focal point of an infrared laser and are releasing extra energy in the form of bluish-white photons. The plasma doesn’t last long, so the way to make a display is to use a laser that scans through a volume of air very quickly, firing tens or hundreds of of thousands of times per second to create a sequence of short-lived (nanosecond-scale) voxels that create the effect of a moving image.

However, a nanosecond-scale plasma burst still contains a significant amount of energy; you don’t want to go walking through one of these displays, because it will burn you. Researchers from the University of Tsukuba, Utsunomiya University, Nagoya Institute of Technology, and the University of Tokyo have developed a “Fairy Lights” display system  that uses femtosecond lasers instead. The result is a plasma display that’s safe to touch.

Each one of those dots (voxels) is being generated by a laser that’s pulsing in just a few tens of femtoseconds. A femotosecond is one millionth of one billionth of one second.  The researchers found that a pulse duration that minuscule doesn't result in any appreciable skin damage unless the laser is firing at that same spot at one shot per millisecond for a duration of 2,000 milliseconds. The Fairy Lights display keeps the exposure time (shots per millisecond) well under that threshhold:

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).

Even cooler, you can apparently feel the plasma as you touch it:

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.

Well, that’s too bad, but maybe we’ll get more details in the next paper.
imgImages: Yoichi Ochiai/University of Tsukuba

As you can see from the pics and video, these displays are tiny: the workspace encompasses just eight cubic millimeters. The spatiotemporal resolution is relatively high, though, at up to 200,000 voxels per second, and the image framerate depends on how many voxels your image needs.

To become useful as the consumer product of our dreams, the display is going to need to scale up. The researchers suggest that it’s certainly possible to do this with different optical devices. We’re holding out for something that’s small enough to fit into a phone or wristwatch, and it’s not that crazy to look at this project and believe that such a gadget might not be so far away.

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