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内容記述 |
The nitrogen-vacancy (NV) center in diamond has demonstrated a potential of biomagnetic sensing.1 Realization of magnetoencepharlography (MEG) using NV centers requires further improvement of magnetic sensitivity at a target frequency ranges of 0 to 200 Hz. Based on the Ramsey magnetometry, which can in principle reach the standard quantum limit. So far, a sensitivity of 460 fT/VHZ has been reported above 2 kHz.2 However, a sensitivity better than 1 pT/vHz in the DC region below 200 Hz has not yet been realized. To enhance the sensitivity for MEG, it is necessary to increase the signal response to magnetic field variations (Slope) while suppressing the noise in such a low-frequency range. The slope is increased with the Ramsey contrast, the free precession time, and the number of detected fluorescence photons. On the other hand, "intensity" noises caused by the laser and acousto-optic modulator may be suppressed by lock-in (LI) detection. However, the conventional LI detection extracts only the principal component at its demodulation frequency, so a part of the transient fluorescence signal is also filtered out. In this study, we focus on enhancing the contrast. Our core idea is to acquire higher-order harmonic signals by introducing boxcar averaging. |
