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There are many ways to store data – digitally, on a hard drive or using analog storage technologies such as holograms. In most cases, creating holograms is technically quite complex: high-precision laser technology is often used.
However, if the aim is simply to store data in a physical object, then holography can be done easily, as TU Vienna is now showing: 3D printers can be used to produce panels from ordinary plastic, with QR codes on them e.g. , can be stored. The information is read using terahertz rays (electromagnetic radiation invisible to the human eye).
Holograms as data storage devices
Holograms are completely different from ordinary images. In a normal image, each pixel has a well-defined location. If you tear off a picture, part of its content will be lost.
However, in a hologram, the image is formed by simultaneous contributions from all areas of the hologram. If you take away part of the hologram, the rest still creates the full image (albeit perhaps a blurrier version). For holograms, information is not stored pixel by pixel, but all information is distributed throughout the hologram.
“We have applied this principle to terahertz beams,” says Evan Constable of the Institute of Solid State Physics at the Technical University of Vienna. “These electromagnetic rays range from about a hundred to several thousand gigahertz, which is comparable to radiation from a cell phone or microwave oven, but at a much higher frequency.”
The terahertz radiation is delivered to a thin plastic sheet. The plate is nearly transparent to terahertz rays, but it has a higher refractive index than the surrounding air, so at every point on the plate it slightly changes the incoming wave. “Then every point of the plate emits waves, and all of those waves interfere with each other,” said Evan Constable. “If you adjust the thickness of the plate point by point in the right way, then the superposition of all those waves is will produce exactly the desired image.”
This is similar to throwing many small stones into a pond in a precisely calculated manner so that the water waves produced by all of those stones add up to create a very specific overall wave pattern.
A piece of cheap plastic serves as a high-tech storage unit for valuables
In this way, a Bitcoin wallet address (consisting of 256 bits) can be encoded in a piece of plastic. By shining the correct wavelength of terahertz radiation onto the plastic plate, a terahertz radiation image can be created to accurately generate the required code. “This way you can safely store items worth tens of thousands of euros in an item that only costs pennies,” says Evan Constable.
In order for the board to produce the correct code, the thickness of the board at each point must first be calculated so that it changes the terahertz waves in the correct way. The code to obtain this thickness profile is freely available on Github by Evan Constable and his collaborators. “Once you have the thickness profile, all you need is a regular 3D printer to print the sheet, and you can holographically store the required information,” explains Constable. The aim of this research work is not only to make terahertz wave holography possible, but also to demonstrate how far the technology for processing these waves has come and how precisely this still rather unusual range of electromagnetic radiation can already be used today .
Magazine
scientific report
Research methods
Experimental Study
Research Topics
not applicable
Article title
Encoding terahertz holograms using computer-generated 3D-printed phase plates
Article publication date
March 6, 2024
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