A new fiber laser technology for the production of second-order nonlinear effects in materials that usually do not 
support them may result in new options for forming these effects for optical computers, high-speed data processors, and bioimaging. Thus, a team of researchers from Georgia demonstrates a technique, based on red fiber laser to produce the nonlinear effects.
To be more precise, for the laser system they develop an array of small plasmonic gold triangles on the surface of a centrosymmetric titanium dioxide or TiO2 slab in the laboratory. Then the gold structure is illuminated with a pulse of laser beam light. It should be noted that the laser beam operates like an optical switch, it breaks the crystal symmetry of the material.
For instance, the laser beam pulse causes the electron excitation, when it is fired at the array of gold triangles on the TiO2 slab, herewith, such an excitation doubles the frequency of the laser beam from a second laser system as it reflects from the amorphous TiO2 slab. The fiber laser system has been already tested and demonstrated the blue laser beam that “shows the frequency-doubled light and the green beam that controls the hot-electron migration”.
The operating principle of the laser system is based on the optical switch that causes the excitation of high-energy electrons inside the gold triangles, therefore, some electrons go to the titanium dioxide from the triangles’ tips. “Since the migration of electrons to the TiO2 slab primarily happens at the tips of [the] triangles, the electron migration is spatially an asymmetric process, fleetingly breaking the titanium dioxide crystal symmetry optically.”
The red laser beam pulse leads to an instant induced symmetry-breaking effect. Nowadays it is possible to break optically the crystalline symmetry of conventionally linear materials, for example, amorphous titanium dioxide, thus, the fiber laser system allows making a range of optical materials wider. These materials can be then employed in numerous micro- and nanotechnology applications such as high-speed optical data processors.
A stable, continuous-wave laser system enables to produce the nonlinear effect last for as long as the fiber laser is turned on. Moreover, it is possible to control the number of migrated electrons through the intensity of the red laser beam light. To be more precise, more electrons appear inside the gold triangles when the intensity of the optical switch rises, and more electrons are put into the TiO2 slab. Nonetheless, the fiber laser system still requires future improvements but now it already offers numerous opportunities in the field of nonlinear nanophotonics as well as plays a crucial role in the field of quantum electron tunneling.
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