This is the first reported observation of a second-order Raman spectrum by means of coherent Raman spectroscopy. Optically heterodyned Raman-induced Kerr-effect spectroscopy was used to study the two-phonon Raman peaks of a highly fluorescent sample of diamond with sensitivity exceeding that obtained in spontaneous scattering or other forms of coherent Raman techniques. The frequency of the one-phonon peak was measured to be 1333.1 +/- 0.5 cm(-1). The frequency of the sharp two-phonon peak was measured to be 2668.6 +/- 0.5 cm(-1), in agreement with lower-resolution spontaneous-scattering measurements.
This is the first reported observation of a second-order Raman spectrum by means of coherent Raman spectroscopy. Optically heterodyned Raman-induced Kerr-effect spectroscopy was used to study the two-phonon Raman peaks of a highly fluorescent sample of diamond with sensitivity exceeding that obtained in spontaneous scattering or other forms of coherent Raman techniques. The frequency of the one-phonon peak was measured to be 1333.1 +/- 0.5 cm(-1). The frequency of the sharp two-phonon peak was measured to be 2668.6 +/- 0.5 cm(-1), in agreement with lower-resolution spontaneous-scattering measurements.
Tunable single-frequency lasers are essential for high-resolution spectroscopy and quantum technologies, yet achieving narrow-linewidth performance in compact, scalable systems across the UV-visible spectrum remains a key challenge. Recent work has revealed that Raman scattering in diamond can act as a natural spectral squeezer, where phonon dynamics help suppress frequency noise and concentrates optical power into a single, narrow spectral mode. Experiments at CERN and elsewhere have demonstrated linewidth compression by orders of magnitude, frequency-noise suppression exceeding 10³-10⁴, and pathways toward Schawlow–Townes-limited performance in CW regimes. These results establish Raman phonon damping as a universal mechanism for generating ultra-coherent, widely tunable lasers, opening new opportunities in quantum metrology, optical clocks, and high-resolution spectroscopy.
Tunable single-frequency lasers are essential for high-resolution spectroscopy and quantum technologies, yet achieving narrow-linewidth performance in compact, scalable systems across the UV-visible spectrum remains a key challenge. Recent work has revealed that Raman scattering in diamond can act as a natural spectral squeezer, where phonon dynamics help suppress frequency noise and concentrates optical power into a single, narrow spectral mode. Experiments at CERN and elsewhere have demonstrated linewidth compression by orders of magnitude, frequency-noise suppression exceeding 10³-10⁴, and pathways toward Schawlow–Townes-limited performance in CW regimes. These results establish Raman phonon damping as a universal mechanism for generating ultra-coherent, widely tunable lasers, opening new opportunities in quantum metrology, optical clocks, and high-resolution spectroscopy.
An experimental study of normal and stimulated Raman emission in diamond is presented, including measurements of linewidth, intensity, and angular distribution of radiation having a frequency shift of 1332.0 ${\mathrm{cm}}^{\ensuremath{-}1}$. The diamond crystal formed a Raman resonator; excitation was by a giant-pulse ruby laser. The dependence of normal Stokes emission on laser intensity and the threshold for oscillation were investigated. A value for the Raman gain ($g=6.9\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ ${\mathrm{cm}}^{\ensuremath{-}1}$ per MW/cm2) was calculated from the measured linewidth ($\ensuremath{\Delta}\ensuremath{\nu}=2.04$ ${\mathrm{cm}}^{\ensuremath{-}1}$) and cross section for scattering, and found to be in good agreement with a value determined from the threshold for oscillation. The angular distributions of anti-Stokes and Stokes emission and absorption for parallel and convergent laser light are also in good agreement with theory: The emission cone angles are strongly dependent on the angle of convergence of the incident light, and it is established that the preferred directions for emission are those making use of the most intense first-order Stokes radiation which is peaked in the forward direction within the Raman resonator.
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.
With the development of quantum optics, photon correlations acquired a prominent role as a tool to test our understanding of physics, and played a key role in verifying the validity of quantum mechanics. The spatial and temporal correlations in a light field also reveal information about its origin, and allow us to probe the nature of the physical systems interacting with it. Additionally, with the advent of quantum technologies, they have acquired technological relevance, as they are expected to play an important role in quantum communication and quantum information processing. This thesis develops techniques that combine spontaneous Raman scattering with Time Correlated Single Photon Counting, and uses them to study the quantum mechanical nature of high frequency vibrations in crystals and molecules. We demonstrate photon bunching in the Stokes and anti-Stokes fields scattered from two ultrafast laser pulses, and use their cross-correlation to measure the 3.9 ps decay time of the optical phonon in diamond. We then employ this method to measure molecular vibrations in CS2, where we are able to excite the respective vibrational modes of the two isotopic species present in the sample in a coherent superposition, and observe quantum beating between the two signals. Stokes scattering, when combined with a projective measurement, leads to a well defined quantum state. We demonstrate this by measuring the second order correlation function of the anti-Stokes field conditional on detecting one or more photons in the Stokes field, which allows us to observe a phonon modeâ s transition form a thermal state into the first excited Fock state, and measure its decay over the characteristic phonon lifetime. Finally, we use this technique to prepare a highly entangled photon-phonon state, which violates a Bell-type inequality. We measure S = 2.360 ± 0.025, violating the CHSH inequality, compatible with the non-locality of the state. The techniques we developed open the door to the study of a broad range of physical systems, where spectroscopic information is obtained with the preparation of specific quantum states. They also hold potential for future technological use, and promote vibrational Raman scattering to a resource in nonlinear quantum optics -- where it used to be considered as a source of noise instead.
In this work, we study the correlated Stokes-anti-Stokes (SaS) Raman scattering in a diamond sample and the influence that the excitation pulse width has in the intensity of generation of the correlated pairs in the process. For this investigation, we used two excitation systems with different temporal pulse width, one with femtosecond temporal width and one with picosecond temporal width. We did two distinct experiments with this excitation systems with difference in the way of filtering the signal: In the first experiment, the signal filtering is made with band-pass filters, this configuration has a greater efficiency that allow us compare better the correlated pair formation efficiency between the different excitation systems. In the second experiment, we used a monochromator to filtering the signal, this configuration allow us to change the wavelength of the detection so we can measure the formation spectrum of the correlated pairs. The results obtained from these experiments show us that the correlated pairs generation efficiency is larger with the use of the system with femtosecond temporal width, what is expected for a non-linear process. In the resonant Raman frequency region, we observed a intensity 1.5 times larger with the use of femtosecond system, and in the out-of-ressonance Raman region, we observed a intensity 5 times larger in the region with lowest Raman shift and 9 times larger in the region with largest Raman shift. We also measure the formation pairs spectrum around the first order Raman peak of the diamond, confirming the existence of a asymmetry in the formation of this pairs with respect to the positive versus negative detuning from phonon resonance. This asymmetry still remains without a satisfactory theoretical explanation.