A high-resolution resonant Raman spectroscopy system has been developed by using optical fibers and applied to the spin-flip Raman scattering experiment in CdZnTe/ CdZnMnTe quantum wells at 3 He temperature in a high magnetic field up to 14 T. Excitation light from an external cavity laser diode or Ti:sapphire laser was introduced into the liquid 3 He chamber by using polarization maintain fiber, and was incident on the sample at the angle of 45 degree through a GRIN collimation lens and a prism to deflect the reflected light from the luminescence/scattering detection pass. Luminescence and scattered light were collected efficiently into the bundled multi-mode fibers through a high NA objective lens and introduced into the slit of a 1.26 m single grating spectrometer equipped with a multi-channel CCD detector and a photon counter. The fiber system provides a convenient way to investigate the spin dynamics in an ideal environments; ultra-low temperature and radiation-free condition. Furthermore, the system is more sensitive than the conventional system utilizing a cryostat with the optical windows where multiple Fresnel loss and the small numerical aperture degrade the sensitivity.
A high-resolution resonant Raman spectroscopy system has been developed by using optical fibers and applied to the spin-flip Raman scattering experiment in CdZnTe/ CdZnMnTe quantum wells at 3 He temperature in a high magnetic field up to 14 T. Excitation light from an external cavity laser diode or Ti:sapphire laser was introduced into the liquid 3 He chamber by using polarization maintain fiber, and was incident on the sample at the angle of 45 degree through a GRIN collimation lens and a prism to deflect the reflected light from the luminescence/scattering detection pass. Luminescence and scattered light were collected efficiently into the bundled multi-mode fibers through a high NA objective lens and introduced into the slit of a 1.26 m single grating spectrometer equipped with a multi-channel CCD detector and a photon counter. The fiber system provides a convenient way to investigate the spin dynamics in an ideal environments; ultra-low temperature and radiation-free condition. Furthermore, the system is more sensitive than the conventional system utilizing a cryostat with the optical windows where multiple Fresnel loss and the small numerical aperture degrade the sensitivity.
T. Blasberg: Coherent Raman scattering for optical detecti¬ on of NMR in Pr3+:YA103. Nuclear magnetic resonance (NMR) is a powerful and versatile spec¬ troscopic technique. However, conventional NMR requires samples, which has to consist of at least 1017 nuclear spins. One of the most promising approaches to increase the sensitivity of this method relies on the resonant interaction of laser fields with atoms. The main goal of this thesis was the investigation and the improvement of coherent Raman scattering techniques for an optical heterodyne detection of NMR. All ex¬ periments were performed at cryogenic temperatures on Pr3+-ions, which were added to the host lattice YAIO3 (YAP). The coherent Raman scattering experiments consist of two distinct stages: firstly, the transient or continuous excitation of a coherent superposition between two nuclear spin states and secondly, its optical detection through coherent Raman scattering of a resonant, frequency-tunable test laser field from this sublevel coherence. For the theoretical description of the experiments, coherent Raman scattering in multilevel atoms is discussed in detail and a common solution for the Raman heterodyne beat signal in pump-and-probe experiments is derived. The dynamics of a three-level atom that interacts with two resonant electromagnetic fields is treated making use of the density-matrix formalism. The method of Raman heterodyne detection of NMR uses a resonant radio frequency field to drive the magnetic-dipole transition between two nuclear spin states. This technique was used to determine the orientation of the nuclear quadrupole tensors of Pr3+ at its two non-equivalent lattice sites in YAP by measuring the dependence of the transition frequencies on the orientation of an external magnetic field. In the electronic ground state 3H4, the quantization axes of the nuclear spin eigenfunctions are ro¬ tated by po=±56.4° relative to the crystal b-axis. The corresponding rota¬ tion angle in the electronically excited state !D2 is Po=±105.2°. With this new value for the relative orientation of the quantization axes in both electronic states, the relative strengths of all 3H4 1D2 transitions could be calculated. The different orientation of the quantization axes in the two electronic states gives rise to a strong state mixing of the nuclear spin eigenfunctions and is the reason, why most of the optical transitions be¬ tween nuclear spin substates of different electronic states have similar oscillator strengths. Pr:YAP is therefore an ideal model system for the investigation of coherent Raman scattering. A new rf-optical triple-resonance experiment was developed that is a combination of Raman heterodyne detection of NMR and spectral holeburning. This technique allows the unambiguous determination of the ab¬ solute sign of nuclear quadrupole coupling constants. In the electronic ground state of PnYAP, the quadrupole coupling constant was found to be negative (D=-3.5289 MHz) being the result of dominant pseudoquadrupole contributions. The pump-and-probe technique, which uses a frequency-tunable test laser beam, was used to investigate the influence of an inhomogeneous broadening of the optical resonance line on Raman heterodyne detection of NMR. A hitherto unknown interference effect could be predicted and verified by the experiments. A prerequisite for this interference effect is that coherent Raman scattering in different opti¬ cal transitions can contribute to the total Raman heterodyne beat signal. These optical transitions represent different 'scattering pathways', whose contributions to the total beat signal can interfere destructively with each other, since the heterodyne beat signal depends linearly on the relevant transition matrix elements. The rf-optical triple resonance technique al¬ lows to circumvent this interference effect, since the frequency-tunable test laser field can be used to select only one of the various scattering pathways. A new and efficient excitation scheme was developed, which allows the observation of coherent Raman beats in systems with arbitrary wide sublevel spectra and small oscillator strengths. The method utilizes a bichromatic laser field for the purely optical excitation of a coherent superposition between two nuclear spin substates. For the preparation of the sublevel coherence, the two frequency components couple two different nuclear spin substates of the same electronic state to a different electronic state. With the help of the density-matrix formalism, the dyna¬ mics of a three-level atom during the bichromatic excitation were calcu¬ lated. Those experimental parameters could be identified that determine the excitation efficiency. While in the purely optical method of coherent Raman beats almost 10_1 of the incident test laser photons were coherent¬ ly Raman scattered, the corresponding figure of merit of Raman hetero¬ dyne detection of NMR was less man 10-3. From the decay of hole-burning spectra in the presence of a saturating rf-field the temperature-dependence of the nuclear spin relaxation rates of Pr:YAP was determined in the temperature range 3-9 K. At low tem¬ peratures, the relaxation is dominated by mutual spin flips whereas at higher temperatures Orbach and Raman relaxation become of importan¬ ce. A simple rate-equation model allowed to calculate the entire hole-bur¬ ning spectrum of the crystal.
We report the development and performance of an atomic magnetometer (AM) utilizing the Raman-driven spin noise spectroscopy (RDSNS) technique, which measures the intrinsic spin fluctuations of an atomic medium subjected to a coherent two-photon optical drive. The RDSNS signal is noninvasively detected using a far-off resonant weak probe light utilizing a polarimetric detection scheme. This overcomes the limitations of the small dynamic range and low bandwidth of traditional optically pumped magnetometers (OPMs) or AMs operating in the spin exchange relaxation-free (SERF) regime. We experimentally demonstrate, using both paraffin-coated and buffer-gas-filled vapor cell containing neutral rubidium atoms, that the dynamic range of such magnetometers can reach beyond 150 G while maintaining a dc magnetometer resolution of around 30 pT and a magnetic noise sensitivity of around30pT/Hzat a bandwidth of 100 Hz and a magnetic field of about 0.6 mT. Being an all-optical setup, this instrument is largely immune to interference with stray radio frequency fields and has the potential to be miniaturized and field deployable. One of the practical applications would be to measure variations in geomagnetic fields precisely without having to shield the magnetometer.
A high imaging resolution or a tight focus of a laser beam imposes a certain minimal numerical aperture (NA) of the optical system. Macroscopic high NA lenses constraint strongly the spatial organization of experiments, in particular when imaging or trapping cold atoms inside a vacuum chamber. Multimode fibers, in conjunction with spatial light modulators, offer an interesting alternative to high NA lenses. Indeed, they are flexible optical waveguides with very small transverse dimensions (∼ 100 μm), and reasonably high NA (up to 0.5). For those reasons, the use of multimode fibers for imaging or laser manipulation purposes has been widely studied in the past years. Here, we transfer these techniques to the field of cold atoms with a multimode fiber forming a compact optical bridge between the inside and the outside of an ultra-high vacuum chamber. We manipulate atoms with laser beams produced through the fiber by digital optical phase conjugation with a spatial light modulator. We are able to transport a small cloud of cold rubidium atoms with a moving optical lattice at about 200 μm from the fiber tip. We can then load them in small optical tweezers with a waist of 1.2 μm. By characterizing the propagation of light modes inside the fiber, we numerically invert its transformation and we reconstruct absorption images of the trapped atoms with a resolution of approximately 1 μm. These results pave the way towards the efficient use of multimode fibers in spatially constrained quantum technology platforms relying on cold atoms.
Optical spectroscopy of single impurity molecules in low-temperature solids provides an exquisitely sensitive probe of the structure and dynamics of the specific local environment around the single molecule, unobscured by ensemble averaging. Effects such as spectral diffusion, perturbations by external fields, changes in molecular photophysics, optical switching, dynamics due to amorphous system physics, magnetic resonance of a single molecular spin, and perturbations due to nearby charge transport have all been observed. Because properly chosen single molecules act as two- and three-level quantum systems, a variety of quantum optical effects may be observed, such as photon antibunching, optical Stark effect, and single-photon emission on command. When they carry spin in their ground and excited states, single molecules and other nano-objects open many more experiments in quantum optics and nanophysics, because they are sensitive to magnetic interactions and can serve as readouts for spin systems with long coherence times. As a new class of nanoscale experiments, the ability to optically pump and probe single 2–3-nm-sized molecules in complex systems provides a new window into the local dynamics and heterogeneity of solids.
Spin-exchange relaxation free alkali-metal magnetometers typically operate in the regime of high optical density, presenting challenges for simple and efficient optical pumping and detection. We describe a high-sensitivity Rb magnetometer using a single elliptically polarized off-resonant laser beam. Circular component of the light creates relatively uniform spin polarization while the linear component is used to measure optical rotation generated by the atoms. Modulation of the atomic spin direction with an oscillating magnetic field shifts the detected signal to high frequencies. Using a fiber-coupled distributed feedback laser, we achieve magnetic field sensitivity of 7fT/Hz with a miniature $5\ifmmode\times\else\texttimes\fi{}5\ifmmode\times\else\texttimes\fi{}5\text{ }\text{mm}\text{ }\text{Rb}$ vapor cell.
Diamond containing the nitrogen-vacancy (NV) center is emerging as a significant sensing platform. However, most NV sensors require microscopes to collect the fluorescence signals and therefore are limited to laboratory settings. By embedding micron-scale diamond particles at an annular interface within the cross section of a silicate glass fiber, we demonstrate a robust fiber material capable of sensing magnetic fields. Luminescence spectroscopy and electron spin resonance characterization reveal that the optical properties of NV centers in the diamond microcrystals are well preserved throughout the fiber drawing process. The hybrid fiber presents a low propagation loss of ∼4.0 dB/m in the NV emission spectral window, permitting remote monitoring of the optically detected magnetic resonance signals. We demonstrate NV-spin magnetic resonance readout through 50 cm of fiber. This study paves a way for the scalable fabrication of fiber-based diamond sensors for field-deployable quantum metrology applications.