Ultrafast nonlinear optical effects induced by nitrogen-vacancy centers in type-IIa diamond
M. Motojima1,*, T. Nakayama1, H. Shigekawa1, Y. Kainuma2, T. An2, and M. Hase1
1

Department of Applied Physics, Faculty of Pure and Applied Sciences, University of Tsukuba
2School of Materials Science, Japan Advanced Institute of Science and Technology*momari.diamond@gmail.com

Introduction
The optical and magneto properties of the negatively charged nitrogen-vacancy (NV) center in diamond has been extensivelyinvestigated because of its application to quantum sensing, such as magnetic and electric fields and to quantum information
technologies. In most cases, near-infrared luminescence upon the excitation by green laser can be controlled by the irradiation by
microwave, which tunes the optical transition path between the excited and ground states. To extend the optical property of diamondover the current generation of linear optical regime, one requires ultrashort laser pulses, which enables one to induce nonlinear
optical effect, such as the nonlinear refraction and nonlinear absorption. Almeida et al. recently reported on nonlinear optical spectrain high-purity diamond using femtosecond laser pulses [1]. Because of the absence of defect-related bands below the band-gap (Eg =5.5 eV), the two nonlinear optical effects were enhanced for E = Eg/2. Although there are several investigations on nonlinear opticaleffects in diamond and nano-diamonds [2], the effects of the NV center on the nonlinear optical phenomena have not yet been
examined. Here we explore the NV center induced nonlinear optical effects in pure diamond, specifically optical Kerr effect (OKE)and two-photon absorption (TPA) in transparent region using 800 nm light, at which NV related bands will be sensitive.
MethodWe carried out Z-scan measurement to examine nonlinear optical effects, such as OKE and TPA [3]. The Z-scan measurements
were performed using a closed aperture mode. To investigate the time-domain response from the OKE and TPA due to the NV
centers near the sample surface, reflection-type pump-probe measurements for the diamond samples were also carried out at room
temperature. The light source used was a femtosecond amplifier system, which produces 40 fs pulses at a central wavelength of 800
nm at 100 kHz repetition rate. The samples used were type-IIa diamond crystal fabricated by CVD method. To introduce NV centers
30 keV nitrogen ions (N+) were implanted into the diamond samples at the N+ dose levels of 2.0x1011 and 1.0x1012 ions/cm2 (Fig. 1).
The implanted depth deduced from the Monte Carlo calculation (TRIM) was about 30–40 nm. After that, the samples were annealed
at 900–1000 ºC in an argon atmosphere for 1 hour to produce NV centers.
Results and discussion

FIG. 1 Schematic for the production of NV centers.

FIG. 2 The Z-scan results at the laser fluence of 20 mJ/cm2.

Figure 2 shows the results of the Z-scan measurements obtained for different N+ dose levels. Anti-symmetric line shape, whose
peak and valley have not the same amplitude, was observed for all the samples. The anti-symmetric lineshape, with a valley greaterthan the peak, indicates an existence of two-photon absorption [1]. The intensity of the transmittance change becomes larger when
the NV centers were introduced at 2.0x1011 and 1.0x1012 N+ /cm2. In particular, the valley at z = -0.2 mm exhibits ≈1.3 times larger
transmission change compared to the pure diamond (non-implanted), indicating that absorption by NV centers plays a central role in
the enhancement of the signals in Figs. 2(b) and 2(c). In addition, pump-probe reflectivity data demonstrate that the OKE signal isstrongly enhanced for 1.0x1012 N+ /cm2. We suggest that the strong enhancement of the OKE is possibly originated from cascading
OKE, where the high-density NV centers effectively break the inversion symmetry near the surface region of diamond [4].

References
1J. M. P. Almeida et al., Sci. Rep. 7, 14320 (2017). 2F. Trojanek et al., Opt. Exp. 18, 1349 (2010). 3M. Sheik-Bahae et al., IEEE J.
Quantum Electron, 26, 760-769 (1990). 4M. Motojima et al., Optics Express, 27, 32217 (2019).