Researchers at the University of Tsukuba demonstrated second-order nonlinear optical effects in diamonds by taking advantage of internal color center defects that break inversion symmetry of diamond crystal.
Previously, scientists thought that the inversion-symmetric nature of diamond crystal lattice could only support weaker, odd-order nonlinear optical effects, which depend on the electric field amplitude raised to the power of three, five, and so on. But the team showed diamonds can support second-order nonlinear optical effects when color centers—so-called Nitrogen-Vacancy (NV) centers—are introduced. In these cases, two adjacent carbon atoms in the diamond’s rigid lattice are replaced with a nitrogen atom and a vacancy. This breaks the inversion symmetry and permits even-order nonlinear processes to occur, which include more useful outcomes that scale as the electric field squared.
The team used chemical vapor-deposited single-crystal diamonds (from Element Six), with extra nitrogen ions implanted to encourage the formation of NV centers. The emission spectrum they observed when the diamonds were excited with 1350-nm light showed clear second- and third-order harmonic peaks.
These observations represent the merging of two or three photons, respectively, into a single photon of higher energy.
This research may lead to faster internet communications, all-optical computers, and even open a route to next generation quantum sensing technologies. (Phys.org)
The paper has been published in ACS Photonics.