Application of the Raman heterodyne technique for the detection of EPR and ENDOR

Abstract

Raman heterodyne detectionis a coherent optical-RF double resonance technique where the optical and RF fields induce coherence within a three level system and a resultant Raman field is measured using heterodyne detection. This approach has been used previously to detect NMR and more recently EPR. In this paper the parameters that affect the amplitude and signal to noise ratio of the Raman heterodyne signals are considered. The power levels in relation to the osciUator strength and dephasing times, the amplitude and spectrum of the laser frequency jitter in relation to the optical homogeneous linewidths and holeburning rates, and the sample properties such as absorption strength and optical quality, are all factors that affect the Raman signal. The presentation is focused on the Raman heterodyne detected EPR of the nitrogen-vacancy pair centre in diamond making comparisons with Raman heterodyne detected NMR signals obtained for rare earth ion systems. RF-RF double resonance studies, RF holeburning and ENDOR, which give information about the hyperfine levels are also reported for the nitrogen-vacancy centre. The resonance frequencies are in agreement with those predicted from the spin Hamiltonian. The factors affecting the lineshapes and relative intensities of the double resonance signals are discussed.

Nitrogen-vacancy center in diamond: Model of the electronic structure and associated dynamics

“…Loubser and van Wyk proposed that the spin polarization arises from a singlet electronic system with inter-system crossing to a spin level of a meta-stable triplet. However, it was established from hole burning [16], optically detected magnetic resonance [17], ESR [18] and Raman heterodyne measurements [19] that the triplet is the ground state rather than a meta-stable state. Therefore, their model has to be modified to give a 3 A ground state and a 3 A − 3 E optical transition.…”

Issues concerning the nitrogen-vacancy center in diamond

“…The N-V center is recognized to have a S ¼ 1 ground and excited state [10][11][12][13][14] and many of the interesting properties of the N-V center are associated with changes in the spin projection [15,6,16]. The electronic states are associated with six electrons occupying dangling bonds in the neighborhood of the vacancy.…”

Electronic structure of the N-Vcenter in diamond: Theory

“…Analysis of hyperfine splittings and EPR intensities 3,12 indicates that coupling of active electrons to nitrogen is weaker in the N-V center than coupling to carbons adjacent to the vacancy. This suggests that active electrons concentrate near these carbons, but does not reveal their number.…”