This device converts laser-beam frequencies at nanoscales without the need for expensive nonlinear optical crystals. Shining laser light beams through certain crystals creates a phenomenon called "second harmonic generation" (SHG), doubling the frequency while halving the wavelength of the light entering the system. The ultimate goal of nanophotonics (a field dedicated to the study of light's behavior at the nanometer scale) is to develop all-optical data processing, a versatile technology with applications in ultrahigh-speed optical sensing, computing, image processing and telecommunications. This goal can only be achieved by manipulating the properties of an optical signal using another optical signal, which requires controlling nonlinear optical phenomena at nanoscale. Researchers at the University of Florida have developed a device, a group of arrays, that achieves second harmonic generation at nanoscale by leveraging key technological principles in this area to their maximum advantage. Extremely efficient, the device converts up to 42 percent of a laser beam's output into a beam of doubled frequency at a scale that approximates the wavelength of the laser's radiation, streamlining development of miniature devices that will double the laser radiation frequency in a controllable way.
A device that facilitates laser-beam frequency conversion at nanoscale
Photons, small units of light that have no mass, move through space-like waves, oscillating up and down in a rhythmic fashion. Visible light makes up only a small portion of the oscillating electric and magnetic fields that travel through space. The color of this electromagnetic radiation is controlled by the number of light waves that pass any given point in space during a set period of time (its "frequency"). University of Florida researchers have developed a system that can alter the laser frequency without the need for optically nonlinear crystals while reducing the effective length at which the conversion occurs to that of the nanoscale. A double array of sub-wavelength dielectric cylinders made of a material with nonlinear susceptibility. The first array is comprised of periodically spaced parallel cylinders. The second array is identical to the first one and positioned parallel at a distance. A source is situated such that it will illuminate the first array with a beam of monochromatic electromagnetic radiation. The geometry of the system (cylinder radius, the period of each array, and the distance between arrays) is set to create a resonator. The incident wave excites a standing wave in the resonator with the property that the electromagnetic field is greatly amplified on the cylinders, which leads to a significant enhancement of optically nonlinear effects and, as a consequence, to second harmonic generation. The field amplification (and, hence, the conversion rate) can be optimized by adjusting the distance between the arrays.
