Researchers currently have recognized that the velocity of light is undoubtedly slowed relatively as it is traveling in substances like liquid or glass.
Nevertheless, it is usually been recently presumed unachievable for particles of light, typically known photons, to be slowed as they cruise throughout free space, unimpeded by interpersonal interactions with any specific elements.

For The Very First Time In History Of Science, Researchers Slow Down The Speed Of Light Travelling Through The Space:

In a new journal submitted in Science Express, scientists from the Faculty of Glasgow and Heriot-Watt University clarifies just how they have got managed to slow down photons in free space for the very first time. They have shown that putting a cover to an optical ray to provide photons a spatial structure may reduce their velocity.

The staff associates a ray of light, that contain a number of photons, to a group of cyclists who relate the effort by taking it in turns to cycle at the front. Even though team then moves along the path as a unit, the velocity of specific cyclists will differ because they change positions.

The team formation makes it tricky to describe a particular velocity for all those cyclists, therefore the same is applicable to light. A single pulse of light has loads of photons, and researchers realize that light pulses are recognized by a number of different velocities.

The team’s research was set up like a time trial race, with couple of photons emitted at the same time across similar distances in the direction of a specified end line. The scientists observed that certain photon hit the finish line as expected, however, the prepared photon which had been reshaped by the cover got there afterwards, this means it had been moving more gradually in free space. After a gap of one meter, the staff calculated a decrease of about 20 wavelengths, many times higher than the measurement accuracy.

The effort illustrates that, after transmitting the light ray throughout a cover, photons flow way more gradually through space. Essentially, this is certainly completely different to the slowing down effect of passing light through a medium like glass or liquid, in which the light is only slowed at that time it is passed via the substance — it approaches to the velocity of light after it emerges the other half. The consequence of transmitting the light via the cover is to restrict the peak velocity at which the photons can travel.

The effort was executed by a group of the Faculty of Glasgow’s Optics Group, headed by Professor Miles Padgett, working together with theoretical physicists led by Stephen Barnett, as well as in cooperation with Daniele Faccio from Heriot-Watt University.

 Daniel Giovannini, one of the leading authors of the journal, said: “The delay we’ve introduced to the structured beam is small, measured at several micrometres over a propagation distance of one metre, but it is significant. We’ve measured similar effects in two different types of beams known as Bessel beams and Gaussian beams.”
Co-lead author Jacquiline Romero said: “We’ve achieved this slowing effect with some subtle but widely-known optical principles. This finding shows unambiguously that the propagation of light can be slowed below the commonly accepted figure of 299,792,458 metres per second, even when travelling in air or vacuum.

“Although we measure the effect for a single photon, it applies to bright light beams too. The effect is biggest when the lenses used to create the beam are large and when the distance over which the light is focused is small, meaning the effect only applies at short range.”

Professor Padgett expressed: “It might seem surprising that light can be made to travel more slowly like this, but the effect has a solid theoretical foundation and we’re confident that our observations are correct.
“The results give us a new way to think about the properties of light and we’re keen to continue exploring the potential of this discovery in future applications. We expect that the effect will be applicable to any wave theory, so a similar slowing could well be created in sound waves, for example.”

The team’s journal, named as ‘Spatially Structured Photons that Travel in Free Space Slower than the Speed of Light’, is published in Science Express, which provides electronic publication of selected papers in advance of print in the journal Science.

Source: University Of Glasgow & Hariot-Watt University.

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