Physicists bring light to a halt for a minute

Physicists in Darmstadt have been able to stop something that has the greatest possible speed and that never really stops: light. About a decade ago, physicists stopped it very for just a moment. In recent years, this extended towards stop times of a few seconds for simple light pulses in extremely cold gases and special crystals. But now the researchers at Darmstadt extended the possible duration and applications for freezing the motion of light considerably.

The physicists, headed by Thomas Halfmann at the Institute of Applied Physics of the Technische Universität Darmstadt, stopped light for about one minute. They were also able to save images that were transferred by the light pulse into the crystal for a minute — a million times longer than previously possible…

To stop the light, the physicists used a glass-like crystal that contains a low concentration of ions — electrically charged atoms — of the element praseodymium. The experimental setup also includes two laser beams. One is part of the deceleration unit, while the other is to be stopped. The first light beam, called the “control beam,” changes the optical properties of the crystal: the ions then change the speed of light to a high degree. The second beam, the one to be stopped, now comes into contact with this new medium of crystal and laser light and is slowed down within it. When the physicists switch off the control beam at the same moment that the other beam is within the crystal, the decelerated beam comes to a stop.

Based on this success, Halfmann’s team now intends to explore techniques that can store light significantly longer — perhaps for a week — and to achieve a higher bandwidth and data transfer rate for efficient information storage by stopped light.


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