<a href=”https://today.ucf.edu/ucf-researchers-develop-way-control-speed-light-send-backward/”>University of Central Florida researchers Abouraddy and study co-author Esat Kondakci demonstrated</a> they could speed a pulse of light up to 30 times the speed of light, slow it down to half the speed of light, and also make the pulse travel backward.
They used a special device known as a spatial light modulator to mix the space and time properties of light, thereby allowing them to control the velocity of the pulse of light. The mixing of the two properties was key to the technique’s success.
“We’re able to control the speed of the pulse by going into the pulse itself and reorganizing its energy such that its space and time degrees of freedom are mixed in with each other,” Abouraddy said.
Nature Communications – Optical space-time wave packets having arbitrary group velocities in free space
Abstract-Controlling Light Pulses
Controlling the group velocity of an optical pulse typically requires traversing a material or structure whose dispersion is judiciously crafted. Alternatively, the group velocity can be modified in free space by spatially structuring the beam profile, but the realizable deviation from the speed of light in vacuum is small. Here we demonstrate precise and versatile control over the group velocity of a propagation-invariant optical wave packet in free space through sculpting its spatio-temporal spectrum. By jointly modulating the spatial and temporal degrees of freedom, arbitrary group velocities are unambiguously observed in free space above or below the speed of light in vacuum, whether in the forward direction propagating away from the source or even traveling backwards towards it.
They synthesize space-time (ST) wave packets using a phase-only spatial light modulator (SLM) that efficiently sculpts the field spatio-temporal spectrum and modifies the group velocity.
The ST wave packets are synthesized for simplicity in the form of a light sheet that extends uniformly in one transverse dimension over ~25 mm, such that control over vg is exercised in a macroscopic volume of space. They measure vg in an interferometric arrangement utilizing a reference pulsed plane wave and confirm precise control over vg from 30c in the forward direction to −4c in the backward direction. They observe group delays of ~±30 picoseconds (three orders-of-magnitude larger than those in references.), which is an order-of-magnitude longer than the pulse width, and is observed over a distance of only ~10 mm. Adding to the uniqueness of their approach, the achievable group velocity is independent of the beam size and of the pulse width. All that is needed to change the group velocity is a reorganization of the spectral correlations underlying the wave packet spatio-temporal structure. The novelty of our approach is its reliance on a linear system that utilizes a phase-only spatio-temporal Fourier synthesis strategy, which is energy efficient and precisely controllable. Their approach allows for endowing the field with arbitrary, programmable spatio-temporal spectral correlations that can be tuned to produce—smoothly and continuously—any desired wave packet group velocity. The versatility and precision of this technique with respect to previous approaches is attested by the unprecedented range of control over the measured group velocity values over the subluminal, superluminal, and negative regimes in a single optical configuration. Crucially, while distinct theoretical proposals have been made previously for each range of the group velocity (e.g., subluminal, superluminal, and negative spans), our strategy is—to the best of their knowledge—the only experimental arrangement capable of controlling the group velocity continuously across all these regimes (with no moving parts) simply through the electronic implementation of a phase pattern imparted to a spectrally spread wave front impinging on a SLM.
SOURCES- University of Central Florida, Nature Communications
Written By Brian Wang, Nextbigfuture.com
Wang is a prolific business-oriented writer of emerging and disruptive technologies. He is known for insightful articles that combine business and technical analysis that catches the attention of the general public and is also useful for those in the industries. He is the sole author and writer of nextbigfuture.com
, the top online science blog. He is also involved in angel investing and raising funds for breakthrough technology startup companies.
He gave the recent keynote presentation at Monte Jade event with a talk entitled the Future for You. He gave an annual update on molecular nanotechnology at Singularity University on nanotechnology, gave a TEDX talk on energy, and advises USC ASTE 527 (advanced space projects program). He has been interviewed for radio, professional organizations. podcasts and corporate events. He was recently interviewed by the radio program Steel on Steel on satellites and high altitude balloons that will track all movement in many parts of the USA.
He fundraises for various high impact technology companies and has worked in computer technology, insurance, healthcare and with corporate finance.
He has substantial familiarity with a broad range of breakthrough technologies like age reversal and antiaging, quantum computers, artificial intelligence, ocean tech, agtech, nuclear fission, advanced nuclear fission, space propulsion, satellites, imaging, molecular nanotechnology, biotechnology, medicine, blockchain, crypto and many other areas.