We report on experimental measurements of transition strengths for spectral components associated with a driven two-level atom. The measurements involve time- and frequency-domain techniques and are performed in nuclear magnetic transitions of a nitrogen-vacancy colour centre in diamond using the optical Raman heterodyne method. The transition strengths are shown to depend on the characteristics of the driving field in a way readily accounted for by the dressed state formalism and the data provide an experimental confirmation of some elementary expressions frequently used for dressed states.
We report on experimental measurements of transition strengths for spectral components associated with a driven two-level atom. The measurements involve time- and frequency-domain techniques and are performed in nuclear magnetic transitions of a nitrogen-vacancy colour centre in diamond using the optical Raman heterodyne method. The transition strengths are shown to depend on the characteristics of the driving field in a way readily accounted for by the dressed state formalism and the data provide an experimental confirmation of some elementary expressions frequently used for dressed states.
The paper reports on experimental investigations of absorption and dispersion profiles of a strongly driven hyperfine transition at various pump field intensities and detunings when probed by a weak field. The transition lies at 5.4 MHz and corresponds to the Iz=0\ensuremath{\leftrightarrows}-1 nuclear magnetic transition within the electron spin singlet of the 3A ground state of the nitrogen-vacancy (NV) center in diamond. The inhomogeneous linewidth of the transition is 8 kHz whereas the homogeneous linewidth is 2.7 kHz, which is a factor of 3 larger than that limited by the population relaxations. The absorption and dispersion are obtained using Raman heterodyne detection, a coherent optically detected magnetic-resonance technique. Measurements are performed in a situation where there is an anticrossing of the ground-state electron-spin levels, as this leads to an enhancement of the hyperfine transition strengths and the optical sensitivity. Weak probe fields with Rabi frequency 0.6 kHz could then be used. The absorption and dispersion profiles were recorded for on-resonance pump fields of various strengths with Rabi frequencies of 0, 2.1, 3.7, 6.6, 11.8, and 21 kHz. In addition, the responses were recorded for an off-resonance field with a Rabi frequency of 55 kHz and detunings between -40 and +40 kHz. The corresponding response of an idealized driven two-level system has been calculated using an established density-matrix equation of motion formalism.When normalized to the profiles with no driving field, the calculated and experimental profiles are in excellent agreement. The nitrogen-vacancy system provides a very clear experimental illustration of a driven two-level system and some aspects are highlighted. For on-resonance pumping, the dispersion profile consists of a positive and a negative absorptionlike peak separated by twice the pump Rabi frequency. The peaks correspond to a significant signal strength (index of refraction) whereas at the frequency of the peaks in dispersion, the absorption is zero. The corresponding absorption profile consists of two dispersionlike features separated by twice the pump Rabi frequency, and between the two features there is negative absorption or gain. For off-resonance pumping, there are again two features. For example, in absorption response, there is an absorption peak and an amplification peak symmetrically displaced from the pump frequency by the generalized Rabi frequency. In this off-resonance pumping situation, it is pointed out that gain occurs where there is inversion in the dressed state whereas gain for the on-resonance pumping situation is achieved without population inversion in either the bare or dressed state.
Using Raman heterodyne detected nuclear magnetic transition in diamond we have observed dressed state nutation for two situations: (i) pulsed probe + cw pump and (ii) cw probe + pulsed pump. The dressed state Rabi frequencies are measured for the first time and found to have a $sin\ensuremath{\theta}$ and $cos\ensuremath{\theta}$ dependence ($\ensuremath{\theta}$ is a function of pump intensity and detuning). A simple consideration based on the dressed state model gives a satisfactory account of the observed dependence. When a 90\ifmmode^\circ\else\textdegree\fi{} phase shift is introduced, spin locking and strong oscillations are observed.
This thesis describes the Raman heterodyne detection of magnetic resonance in the ³A ground state of the nitrogen-vacancy C'-1· V) centre in diamond. The recently developed theory of Raman heterodyne spectroscopy was tested and compared with the spectra measured on the N-V centre. Among those results, the electron-nuclear double resonance (ENDOR), nuclear-nuclear double resonance (double NMR), Autler-Townes effect, coherence transfer and Zeeman quantum beat were observed for the first time using such techniques. Raman heterodyne techniques were also used to investigate the level anticrossing, hyperfine and nuclear quadrupole interactions, and spin relaxations of the N-V centre with high sensitivity and precision. This thesis is comprised of three parts. Part one includes Chapters 1 to 3, providing introductory accounts. Chapter l is an introduction to the N-V colour centre, which describes the defect configuration, the spin Hamiltonian and the calculations of energy levels and wave functions of the ³A ground state. Chapter 2 briefly describes the theory of Raman heterodyne spectroscopy - a coherent optical radio-frequency (RF) double resonance technique, in particular the Raman heterodyne signals at weak and intense RF fields. Chapter 3 deals with experimental details and techniques utilized in the studies. Part two consists of Chapters 4 and 5, where the Raman heterodyne theory is compared with experimental results. Chapter 4 presents the Raman heterodyne detected nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) lineshapes compared with theoretical results at various RF power levels, laser intensities and laser frequencies within the 6380A zero-phonon line. The double resonance spectra obtained by Raman heterodyne techniques are discussed in Chapter 5, where attention is paid to the analysis of their spectral profiles depending on the detection scheme. The application of Raman heterodyne techniques to the studies of magnetic resonance of the N-V centre is described in part three, consisting of Chapters 6 to 9. The EPR measurements are described in Chapter 6, which were used to study various interactions near the level anticrossing, in particular the spin alignment. The hyperfine and nuclear quadrupole interactions probed by the NMR, ENDOR and hole burning measurements are described in Chapter 7. From these measurements, the hyperfine and quadrupole parameters in the spin Hamiltonian were fully determined. Chapter 8 deals with the Autler-Townes effect in the NMR and EPR transitions. By measuring the Autler-Townes spittings, the magnitudes of matrix elements of the NMR transitions were examined and compared. Chapter 9 presents the coherent spin transient properties, including nutations, echoes, Zeeman beating and coherence transfer. The dephasing time and homogeneous linewidths of the NMR and EPR transitions were then determined from the echo measurements. Finally, the thesis is summarized in Chapter 10.
This thesis studies the interaction between two-and three-level systems and strong, coherent radio-frequency (rf) electrom agnetic fields.The investigations were carried out in both the frequency domain, where steady state properties are examined, and the time domain, where transient behaviours are studied.The two-and three-level systems studied arise from the nuclear spin I = 1 triplet within the 3 A ground state of the nitrogen-vacancy (N-V) centre in diamond.The nuclear magnetic resonance (NMR) is detected optically using a coherent optical-rf double resonance Raman heterodyne technique.Owing to the unique features of both the nuclear spin triplet and the detection technique, many interesting experimental results have been obtained.The thesis is comprised of four parts.Part 1 includes Chapters 1 to 3, which provides introductory accounts.The two-level system concept and associated theoretical treatments in the density matrix formalism are introduced in Chapter 1.The theory is given in a very general form and is developed later in relevant chapters for specific situations.Chapter 2 gives an introduction to the N-V centre and its electronic and hyperfine energy levels.The Raman heterodyne technique and the experimental details are described in Chapter 3.In Part 2, consisting of Chapters 4 and 5, the nuclear magnetic transition of interest is characterized.Chapter 4 describes various coherent transient observations including nutation, free-induction-decay (FID), spin echo, spin locking, delayed FID, and rotary echo, from which important parameters such as the transition strength, population decay time T 1? and dephasing time T2 can be deduced.The dependence of these parameters upon the wave function mixing due to the level anti-crossing is discussed in Chapter 5.Part 3 is the most significant part of the thesis and consists of Chapters 6 to 9. In these chapters the interaction of a two-and three-level system with electromagnetic fields are studied in the frequency domain using pump-probe spectroscopy.This technique involves driving the systems with a strong (pump) field and monitoring it with a separate (probe) field.The absorption and dispersion profiles of a driven two-level system probed by a weak field are discussed in Chapter 6. Topics include the dynamic "Stark" effect and amplification without inversion.When the probe intensity is increased from weak to strong, multiphoton transitions and multiphoton gain without inversion are observed.These effects are described in Chapter 7. When the pump and probe fields interact separately with two transitions which share one common level the two-level system is extended to a three-level one.The power broadening of the Autler-Townes spectrum in such a three-level system is the topic presented in Chapter 8. Chapter 9 considers the case where there are two strong fields and a weak probe field.The discussion is in terms of the dressed state picture and it is shown that the dressed state can be also dressed.Experimental results of the transient nutation in dressed states are presented in part 4 which consists of Chapter 10.The dressed states transition strength is determined for the first time experimentally.Finally, Chapter 11 presents a summary of this thesis.
Raman-heterodyne-detected complex nonlinear susceptibility has been measured and analyzed in detail with a radio-frequency field strength varying from weak to strong. The experiments were carried out on the nitrogen–vacancy color center in diamond involving both nuclear magnetic resonance and electron paramagnetic resonance transitions. The dispersive and the absorptive components of the nonlinear susceptibility are shown to have different saturation behaviors, and an anomalous-amplitude line shape arises where the dispersion component dominates in the response spectrum at high RF powers. The experimental results are found to be in good agreement with theoretical profiles, where no adjustable parameter is included in the calculation.
The Autler–Townes effect in nuclear magnetic resonance (NMR) and electron paramagnetic resonance has been observed using recently developed Raman heterodyne techniques. The measurements were carried out on the nitrogen-vacancy color center in diamond, where the 3A↔3E optical transition was driven by a single mode dye laser at 638 nm while the magnetic transitions in the 3A ground state were driven by two rf fields. The measured splittings in the NMR lines were found to be in good agreement with theoretical predictions. Using the Autler–Townes effect, the magnitude of the dipole moments of the mI=0↔±1 (mS=0) transitions in the ground state was determined, and found to be the same. Comparison of this latter result with the NMR spectra shows that Raman heterodyne signal intensities are determined by population factors.