Researchers Develop Source For THz Radiation

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Researchers have recently developed a nano-antenna by taking advantage of surface states.

Nano antennas are different from conventional antennas because they are not used to carry our embedded sound waves or data from one place to another. These antennas are used to gain understanding about what is happening on an atomic scale.

Researchers from the University of California, Los Angeles have developed a nano-antenna by taking advantage of surface states. The surface states created by the left-over bonds that are inevitable on the outside of a crystal lattice can create high gradient electric fields as they interact with the semiconductor. The incident photons can interact with this field.

“Incoming light can hit the electrons in the semiconductor lattice and move them to a higher energy state, at which point they are free to jump around within the lattice,” according to UCLA. “The electric field created across the surface of the semiconductor further accelerates these photo-excited high-energy electrons, which then unload the extra energy they gained by radiating it at different optical wavelengths, thus converting the wavelengths.”

To enhance this process of interaction, the researchers built a nano-antenna array on the surface of the InAs.

“The nano-antennas have two major functions: one is the efficient excitation of surface plasmon waves and the other is the efficient and broadband radiation of terahertz waves,” UCLA engineering professor Mona Jarrahi said.

The coupled surface states can down-convert 1550nm optical wavelengths to terahertz frequencies four-orders of magnitude more efficiently than non-linear optical methods, according to UCLA.

“Whenever two monochromatic optical waves [two different wavelength components of the 1550nm pulse in this case] have a spatial overlap along their propagation path, the superposition of their fields provides an effective electric field envelope with a beat frequency equal to their frequency difference,” explained Jarrahi.

“Through this new framework, wavelength conversion happens easily and without any extra added source of energy as the incoming light crosses the field,” said research engineer Deniz Turan.


 

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