Ultra-fast Light Pulses can Now be Sculptured

What will it feel like if we are able to mold the light pulses in whatever way we want? Scientists have figured out a novel way to do so.

Researchers from the University of Maryland and the National Institute of Standards and Technology (NIST) joined forces with each other to come up with a compact method of sculpting light pulses. They started their experiment by depositing a layer of ultrathin silicon on extremely thin (few hundred nanometers) sheets of glass. Once the silicon was applied, the researchers covered these tiny squares with protective material and used a strong acid to remove the silicon surrounding each of them. This resulted in millions of tiny pillars, which proved instrumental in developing this latest light-sculpting method.

Properties of Light Pulses

The product of this experiment is a nanopillar that acts as a clear example of a metasurface. Such a material alters the properties of a light pulse while the wave is passing through it. Custom designing of these nanopillars enabled the researching team to control multiple properties of the passing light pulses. Some of these properties are phase, amplitude, and polarization of the light wave. Given the importance of its applications, this ultrathin device is being regarded as a massive achievement in the scientific community.

Adjusting the properties of light pulses is critical for transferring data through the high-speed optical circuits. Similarly, it is a useful tool for analyzing atoms and molecules that oscillate trillions of times within a second. Currently, spatial light modulators are being used for pulse shaping but they are costly and lack the control that scientists are looking for. Another problem with this device is that it uses liquid crystals which can be tampered by the high-intensity light pulses they were designed to shape. All these factors make this discovery even more significant. Amit Agarwal, a Researcher at NIST, talked about the simultaneous manipulation of multiple properties of light pulses in the following words:

“We figured out how to independently and simultaneously manipulate the phase and amplitude of each frequency component of an ultrafast laser pulse. To achieve this, we used carefully designed sets of silicon nanopillars, one for each constituent color in the pulse, and an integrated polarizer fabricated on the back of the device.”

The Behavior of Silicon Nanopillars

The phase of a light pulse is delayed when it travels through a set of silicon nanopillars because the speed of the wave is reduced (in comparison to air) inside these devices. The extent of this variation is determined by the size of these nanopillars. On the other hand, their orientation is responsible for the change in the polarization of the light wave. Similarly, the change in amplitude can be translated by attaching a Polarizer to the device.

A specific, controlled change in these any of these characteristics can be used to encode information. Likewise, rapid changes can be used to either change or study the outcome of different chemical and biological processes. This attribute of these nanopillars opens up a lot of new possibilities in the field of high-speed communication. Henri Lezec, another Researcher from NIST, acknowledged to the potential of this technology by saying,

“We wanted to extend the impact of metasurfaces beyond their typical application — changing the shape of an optical wavefront spatially — and use them instead to change how the light pulse varies in time.”

Individual Frequency Components

The researching team used Diffraction Grating, an optical device, to separate the individual colors of the light pulse as a typical light wave is simply too fast to shape at one particular instant. Each of these colors has a different amplitude and struck different sets of nanopillars when directed onto the silicon surface. All the nanopillars were tailored to alter the polarization and phase of the striking color in a different way. Lastly, another diffraction grating was used to get the newly formed pulse by recombining all the components.

The design of this nanopillar system enabled the scientists to work with a broad range of frequency components, having their wavelengths in the range of 700-900 nanometers. The results of the research showed that this method can split, compress, and distort light pulses, quite efficiently. The researching team is hopeful that further improvement in the technology will give them additional control over light pulses that could lead to some amazing discoveries, in the coming years.   

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