Data transmission from space to earth with laser filaments

Could light be used to transmit information between satellites and the Earth? Atmospheric water vapor disperses and absorbs light energy, but overcomes that obstacle and the light will carry much more information and move it faster than the radio waves we currently rely on. A new research project, supported by the National Geospatial-Intelligence Agency, proposes to use the properties of light itself to open a data path through clouds.

“My job is to understand the constituents of light and manipulate them to interact with matter. In recent years, we have seen more advances in the use of light for biomedical imaging and quantum computing, but the fundamental properties of light manipulation they are the same and light can be made to make this work, ”said Moussa N’Gom, assistant professor of physics at Rensselaer Polytechnic Institute.

The use of light to move data wirelessly, known as optical communication in free space, is common in applications that require only short trips, such as infrared remote controls. But the reliability, quality, and stability of light-transmitted data plummets when used over any substantial distance within the Earth’s atmosphere. Just as sunlight heats clouds and refracts in a diffuse glow, data that travels like light is scattered and lost among the gases of the atmosphere.

In his laboratory, N’Gom manipulates the three main components of light: polarization, which controls the direction of the light’s electric field; phase, which alters the way light interacts with its environment; and the amplitude of light waves, to create specialized light with unusual capabilities. It can use light to create images of living tissue, cut hard materials with precision, or improve optical communication.

To send data through the atmosphere, N’Gom uses a laser configured to generate a pulse of light so short, intense and uniform that it will create a tiny sphere of plasma, a superheated gas created by the interaction between the pulse and water vapor. of the clouds – in the air along the path of light.

The plasma ball continues to absorb energy from additional pulses, which in turn causes it to refocus and redirect the incoming pulses and generate an additional plasma ball along the path of light. Then the cycle repeats itself.

This cascading effect, resulting from the repetitive interaction between the pulse train and the plasma, can generate a laser filament up to 100 meters long. Along that filament, the plasma spheres produce an acoustic wave that disperses the water vapor around it. And in the transparent tunnel that forms around the laser filament and its plasma envelope, N’Gom can deliver a second donut-shaped data stream that travels from space to Earth without degrading.

Each pulse lasts only on the order of a femtosecond, 10X-15 seconds, an incredibly short time during which light travels about 6 microns, or the width of a human hair.

“In this very, very short period of time, I can deliver a lot of energy very quickly, all at once,” N’Gom said. “And that breaks the atmosphere. It’s very short, but it’s so strong and focused in one point, and you’ll have a whole line of it, creating a hole in the clouds that we can use to send information.”

Although each pulse is made up of light in the visible spectrum, with wavelengths between 400 and 800 nanometers, and packs an enormous amount of energy over its duration, they are so short that the system will not be visible, nor will it pose harm. to life or the environment.

The “Free Space Optical Communication Through Dynamic Media” project is supported with a three-year $ 600,000 grant.

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