September 30, 2022

Diamond color centers for nonlinear photonics

Diamond color centers for nonlinear photonics The nonlinear emission spectrum from diamond crystal with NV centers (NV diamond) excited with IR laser (1350 nm). Both SHG and THG are simultaneously generated at 675 nm and 450 nm, respectively. An inset photograph was taken during the nonlinear emission (SHG and THG) from the NV diamond. Credit: University of Tsukuba

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. (

The paper has been published in ACS Photonics.

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