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Title: Techniques in the optical detection of magnetic resonance using nitrogen-vacancy centre ensembles in diamond
Author: Macrae, Calum Donald
ISNI:       0000 0004 7967 2626
Awarding Body: University of Strathclyde
Current Institution: University of Strathclyde
Date of Award: 2018
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Studies were performed to progress the application of nitrogen-vacancy (NV) centres to the sensing of magnetic fields. A magnetometer using an NV centre ensemble contained within a 150 μm diameter diamond was built. Using an adapted epi-fluorescence microscopy setup and 2 mW of optical excitation, a sensitivity of 70 ± 26 nT/Hz1/2 was achieved with a bandwidth of 3.1 kHz. This was 110 times above the shot-noise limit of 639 pT/Hz1/2 and 1129 times above the spin projection noise limit of 62 pT/Hz1/2. This was likely due to noise in the laser, microwaves and detectors. The experimental method requires large improvements in spin dephasing time (T2*) to enable the intended detection of marine worm action potentials via bio-magnetism. Secondly, two-photon excited optical detection of magnetic resonance (2PODMR) of NV centre ensembles was successfully demonstrated. This proves two-photon excited magnetometry with NV centres possible. The 2PODMR linewidth and contrast were found to be reduced by 39.6 % and 73.7 % respectively, when compared with measurements of single-photon excited ODMR. The reduction in ODMR contrast can only partially be explained by the increased temperature and lower NV-/NV0 ratio under two-photon excitation. Two-photon excited fluorescence was also found to saturate at low fluorescence rates compared with single-photon excited fluorescence. This is likely to be related to previously measured effects where 1064 nm excitation has quenched 532 nm excited fluorescence. Finally, a first step towards building a magneto-sensitive laser using NV centres for ultra-sensitive magnetometry was made. Direct measurements of stimulated emission from NV centre ensembles contained within a mm scale diamond were attempted but were inconclusive. Despite measuring a change in probe power using a pump-probe setup, the wavelength, power and temporal dependencies were not fully consistent with a measurement of stimulated emission. However, ODMR was successfully measured using the probe beam.
Supervisor: McConnell, Gail ; Riis, Erling Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral