A multi-institutional team of researchers that included scientists with the Lawrence Berkeley National Laboratory (Berkeley Lab) has created the first artificial molecules whose chirality can be rapidly switched from a right-handed to a left-handed orientation with a beam of light. This holds potentially huge possibilities for the application of terahertz technologies across a wide range of fields, including biomedical research, homeland security and ultrahigh-speed communications.
Working with terahertz (THz) metamaterials engineered from nanometer-sized gold strips with air as the dielectric – Zhang and his colleagues fashioned a delicate artificial chiral molecule which they then incorporated with a photoactive silicon medium. Through photoexcitation of their metamolecules with an external beam of light, the researchers observed handedness flipping in the form of circularly polarized emitted THz light. Furthermore, the photoexcitation enabled this chirality flipping and the circular polarization of THz light to be dynamically controlled.
“In contrast to previous demonstrations where chirality was merely switched on or off in metamaterials using photoelectric stimulation, we used an optical switch to actually reverse the chirality of our THz metamolecules,” Zhang says.
The optically switchable chiral THz metamolecules consisted of a brace of 3D meta-atoms of adverse chirality fabricated from absolutely structured gold strips. Anniversary meta-atom serves as a resonator with a coupling amid electric and alluring responses that produces able chirality and ample annular dichroism at the resonance frequency.
“When two chiral meta-atoms of the aforementioned appearance but adverse chirality are accumulated to anatomy a metamolecule, the mirror agreement is preserved, consistent in the vanishing of optical activity,” Zhang says. “From a altered point of view, the optical action arising from these two meta-atoms of adverse chirality cancels out anniversary other.”
Silicon pads were alien to anniversary chiral meta-atom in the metamolecule but at altered locations. In one meta-atom, the silicon pad bridged two gold strips, and in the added meta-atom, the silicon pad replaced allotment of a gold strip. The silicon pads bankrupt the mirror agreement and induced chirality for the accumulated metamolecule. The pads additionally functioned as the optoelectronic switches that addled the chirality of the metamolecule beneath photoexcitation.
Says agnate columnist Shuang Zhang, “Our arrangement relies on the aggregate of two meta-atoms with adverse properties, in which one is anatomic while the added is abeyant aural the abundance ambit of interest. With acceptable design, the two meta-atoms acknowledge abnormally to an alien stimulus, that is, the abeyant one becomes anatomic and carnality versa.”