Abstract
Nitrogen-vacancy (NV) center in diamond crystals offers high spatial-resolution quantum sensing based
on controllable photo-luminescence under microwave irradiation. In order to explore possible development
of NV centers toward nonlinear quantum sensing, we investigate the effect of NV centers in single
crystal diamond on nonlinear optical effects using 40 fs femtosecond laser pulses. The near-infrared
femtosecond pulses allow us to study purely nonlinear optical effects, such as optical Kerr effect (OKE)
and two-photon absorption (TPA). We found that both nonlinear optical effects are significantly enhanced
by the introduction of NV centers. In particular, our data demonstrate that the OKE signal is
strongly enhanced for the heavily implanted type-IIa diamond, being possibly originated from cascading
OKE, where the high-density NV centers break the spatial inversion symmetry near the surface region of
diamond.
