Team of physicists over at Darmstadt headed by Thomas Halfmann have succeeded in freezing motion of light for about a minute and also managed to save the images being transferred by the light in the crystal.

Stopping light while in motion is nothing new as about a decade ago researchers were able to stop the motion for short moments following which researchers extended the times to a few seconds using extreme cold gases as well as special crystals.

To achieve the stoppage, Halfmann and his team used a glass-like crystal having low concentration of praseodymium ions, two laser beams – one beam that has to be stopped and the other being part of the deceleration unit also known as the control beam. In the setup, the control beam would change the optical properties of the crystal such that the ions would change the speed of light to a great degree.

The beam which is to be stop is then made to come in contact with the crystal. Because of the change in the optical properties of the crystal, the laser light is slowed within the crystal and as soon as the control beam is switched off while the other beam is inside the crystal, the decelerated beam comes to a stop – to be precise, the light turns into a wave trapped in the crystal lattice.

To reason behind the wave like structure is as follows: the ions inside the crystal have orbiting electrons. One electron when put into motion would propagate the movement in a chain like a wave – if mediated through magnetic forces. Magnetism of electrons is called a “spin”. Thus the “spin wave” is formed in a similar manner when the beam is frozen – a reflection of the beam’s light wave. Using the same mechanism, the physicists were able to store images and retrieve them back once the control beam was switched on.

Halfmann and his team believe that the research will have practical significance in next-gen data processing systems that operate using light.

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