Formation of two-dimensional multichannel vertical optical waveguides in a nitrogen-vacancy center diamond using a femtosecond Bessel beam laser for local quantum sensing

Nitrogen vacancy (NV) centers in diamonds can function as quantum sensors for measuring magnetic fields, temperature, and stress with high sensitivity. They are useful in various biological applications, such as for measuring the local magnetic and electrical fields and signal propagation in tissues as well as their local interaction dynamics. However, to enable measurements suitable for medical applications, an observation system that can noninvasively map neural activity from the magnetic fields generated by brain nerve cells with high spatial resolution and sensitivity is required. We fabricated a vertical waveguide array in a diamond containing nitrogen vacancy (NV) centers with cell size dimension using a green femtosecond Bessel beam laser. The red emission from NV centers within the waveguide is confined inside the waveguide (typically with a cell size of 15 μm) by the total internal reflection at its walls. This enables efficient optical confinement and improves the light collection performance of the NV center emission. We have also developed a sensor—called the diamond micro-NV center array device (MAED)—that allows the observation of local magnetic field distributions and have measured spatial distribution of magnetic field with cell-size accuracy. This approach makes it possible to perform localized measurements of electrical and magnetic properties, as well as dynamic mapping of biological systems. This technological innovation holds a significant potential for the noninvasive observation of functional networks in cortical neurons.