Holograms  

The interactive holograms featured in films like Iron Man and Big Hero 6 may be closer to reality thanks to work done by Japanese researchers with femtosecond lasers.

Researchers in Japan have created a mid-air 3D holographic plasma display that also features haptic feedback.

"This study is the first step to discuss and design laser-based aerial volumetric displays," write the researchers.

The system, demonstrated in the video below, works by way of using a femtosecond laser to turn small pockets of air (voxels) into plasma.

"This study is the first step to discuss and design laser-based aerial volumetric displays."

The holographic system, which will be presented at SIGGRAPH 2015 next month, can render up to 200,000 voxels per second, but the physical size of the display is limited to about a cubic centimeter.

The researchers commented on the details of the theoretical principles, system setup, and experimental evaluations, and also discusses the scalability of the system, along with limitations, and applications. "Although we focus on laser-induced plasma, the same considerations can be applied to
other emission techniques such as fluorescence and cavitation," they write.

A femtosecond laser is a laser that fires for a short burst—on the order of one quadrillionth of a second. The laser hits an atom or molecule, causing an electron to become ionized and then the electron loses its extra energy in the form of a photon that is emitted as visible light.

To transform the single plasma dot into a full 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.

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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 also notes that using a femtosecond laser (as opposed to a picosecond or nanosecond laser) is one of the novel aspects of the system. Because the laser bursts are so short, the plasma is not 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. When touched, the laser feels like sandpaper, says principal investigator Yoichi Ochiai, although some participants thought the plasma felt a little like a static shock.

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.



SOURCE  Popular Science

By 33rd Square

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 Mind Reading  

Using a mathematical model, researchers in The Netherlands have reconstructed thoughts from data collected from fMRI test subjects - essentially they read the minds of the participants.

By analysing MRI images of the brain with an elegant mathematical model, researchers from Radboud University Nijmegen have reconstruct thoughts more accurately than ever before. In this way, they have succeeded in determining which letter a test subject was looking at.

The researchers work has been published in the  journal Neuroimage.

Functional MRI scanners have been used in cognition research primarily to determine which brain areas are active while test subjects perform a specific task. The question is simple: is a particular brain region on or off? A research group at the Donders Institute for Brain, Cognition and Behaviour at Radboud University has gone a step further: they have used data from the scanner to determine what a test subject is looking at.

The researchers 'taught' a model how small volumes of 2x2x2 mm from the brain scans -- known as voxels -- respond to individual pixels. By combining all the information about the pixels from the voxels, it became possible to reconstruct the image viewed by the subject. The result was not a clear image, but a somewhat fuzzy speckle pattern. In this study, the researchers used hand-written letters.

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"After this we did something new", says lead researcher Marcel van Gerven. "We gave the model prior knowledge: we taught it what letters look like. This improved the recognition of the letters enormously. The model compares the letters to determine which one corresponds most exactly with the speckle image, and then pushes the results of the image towards that letter. The result was the actual letter, a true reconstruction."

"Our approach is similar to how we believe the brain itself combines prior knowledge with sensory information. For example, you can recognize the lines and curves in this article as letters only after you have learned to read. And this is exactly what we are looking for: models that show what is happening in the brain in a realistic fashion. We hope to improve the models to such an extent that we can also apply them to the working memory or to subjective experiences such as dreams or visualisations. Reconstructions indicate whether the model you have created approaches reality."

In other words, the researchers claim to be very close to the ability to read your mind with their technique.  Such an understanding may also open up the possibility of implanting thoughts, knowledge or, on a more sinister level, control the actions of individuals without their authority.

"In our further research we will be working with a more powerful MRI scanner," explains Sanne Schoenmakers, who is working on a thesis about decoding thoughts. "Due to the higher resolution of the scanner, we hope to be able to link the model to more detailed images. We are currently linking images of letters to 1200 voxels in the brain; with the more powerful scanner we will link images of faces to 15,000 voxels."


SOURCE  Radboud University Nijmegen

By 33rd Square

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