Development and Evaluation of an Optical-Based Spin-Lattice Relaxometry System for Nitrogen-Vacancy Centers in Nanodiamonds

Trinadia Kurniasari, Dr. Gea Oswah Fatah Parikesit, S.T., M.Sc.; Grace Gita Redhyka, S.T., M.Eng.

2026 | Skripsi | FISIKA TEKNIK

Pusat vakansi-nitrogen atau nitrogen-vacancy (NV) pada nanodiamond memungkinkan penginderaan skala nano dengan kondisi eksperimen yang relatif mudah diakses. Pada sistem relaksometri berbasis optik, waktu relaksasi spin-kisi, T1, diperoleh melalui inisialisasi optik dan pembacaan fluoresensi tanpa eksitasi gelombang mikro. Namun, ekstraksi T1 yang andal masih menjadi tantangan karena sinyal fluoresensi eksperimen dapat dipengaruhi oleh derau, urutan akuisisi, dan variasi sampel. Penelitian ini mengembangkan sistem relaksometri spin-kisi berbasis pusat NV pada nanodiamond, dan mengevaluasi konsistensi dan goodness-of-fit nilai T1 pada variasi konsentrasi Mn2+. Sistem yang dikembangkan terdiri atas komponen optik, elektrik, dan mekanik, dengan sumber eksitasi laser hijau 532 nm berdaya 7 mW dan lebar pulsa 10 µs. Sampel disiapkan pada substrat kaca menggunakan nanodiamond berukuran rata-rata 70 nm dan diberi air atau larutan Mn2+. Metode sampling sekuensial dan sampling acak dengan 10 serta 20 kombinasi dibandingkan. Data peluruhan dianalisis menggunakan model single- dan bi-exponential. Sistem ini berhasil mengamati karakteristik relaksasi pusat NV dan membedakan perlakuan sampel, meskipun perilaku anomali ditemukan pada sampel Mn2+ 1 µM. Nilai T1 yang diperoleh berkisar 4,80–24,48 µs untuk model single-exponential dan 5,34–302,81 µs pada komponen panjang untuk model bi-exponential. Model bi-exponential secara umum merepresentasikan data dengan lebih baik, sedangkan sampling acak mengurangi pengaruh urutan pengukuran.

Nitrogen-vacancy (NV) centers in nanodiamonds enable nanoscale sensing under relatively accessible experimental conditions. In optical-based relaxometry, the spin-lattice relaxation time, T1, is obtained using optical initialization and fluorescence readout without microwave excitation. However, reliable T1 extraction remains challenging because experimental fluorescence signals can be affected by noise, acquisition order, and sample-dependent variations. This study developed a spin-lattice relaxometry system based on NV centers in nanodiamond, and evaluated the consistency and goodness-of-fit of the extracted T1 values across different Mn2+ concentrations. The system consisted of optical, electrical, and mechanical components, including a 532-nm pulsed green laser operated at 7 mW with a 10 µs pulse width. Samples were prepared on glass substrates using 70-nm nanodiamonds and treated with water or Mn2+ solutions. Regular sequential sampling and random sampling with 10 and 20 combinations were compared. The decay data were fitted using single- and bi-exponential models. The system successfully observed NV-center relaxation behavior and distinguished different sample treatments, although anomalous behavior was observed for the 1 µM Mn2+ sample. The average extracted T1 values were 4.80–24.48 µs for single-exponential fitting and 5.34–302.81 µs for the long component of bi-exponential fitting. The bi-exponential model generally described the data better, while random sampling reduced time-dependent effects.

Kata Kunci : relaxometry, quantum sensing, nanodiamond, optical system, NV center