606 research outputs found
A simple setup for in situ alkali metal electronic spin polarimetry
Faraday rotation is considered a gold standard measurement of the electronic spin polarization of an alkali metal vapor produced under optical pumping. However, during the production of large volumes of hyperpolarized xenon gas, transmission monitoring measurements, otherwise known as field cycling measurements, are generally employed to measure the spin polarization of alkali metal atoms in situ as this method is easier to implement than Faraday rotation on standard polarizer setups. Here, we present a simple, low-cost experimental setup to perform Faraday rotation measurements of the electronic spin polarization of alkali metal atoms that can be easily implemented on standard polarizer setups. We then compare Rb polarization measurements obtained with the Faraday rotation method to those obtained with the transmission monitoring method. To our knowledge, a direct comparison of these methods has never been made. Overall, we found good agreement between the two methods, but at low Rb density and high laser power, we found evidence of nonlinear magneto-optical effects that may prevent Faraday rotation from being used under these conditions
Spintronic Sources of Ultrashort Terahertz Electromagnetic Pulses
Spintronic terahertz emitters are novel, broadband and efficient sources of
terahertz radiation, which emerged at the intersection of ultrafast spintronics
and terahertz photonics. They are based on efficient spin-current generation,
spin-to-charge-current and current-to-field conversion at terahertz rates. In
this review, we address the recent developments and applications, the current
understanding of the physical processes as well as the future challenges and
perspectives of broadband spintronic terahertz emitters
Chip-scale atomic magnetometer based on free-induction-decay
This thesis describes the implementation of an optically pumped caesium magnetometer containing a 1:5mm thick microfabricated vapour cell with nitrogen buffer gas, operating in a free-induction-decay configuration. This allows us to monitor the free Larmor precession of the spin coherent Cs atoms by separating the pump and probe phases in the time domain. A single light pulse can sufficiently polarise the atomic sample;however, synchronous modulation of the light field actively drives the precession and maximises the induced spin coherence. Both amplitude- and frequency-modulation have been adopted producing noise floors of 3.4 pT / √Hz and 15.6 pT/√Hz, respectively,within a Nyquist limited bandwidth of 500 Hz in a bias field comparable to the Earth's (~50 μT). We investigate the magnetometers capability in reproducing time-varying magnetic signals under these conditions, including the reconstruction of a 100 pT perturbation using signal averaging.Additionally, we discuss a novel detection mode based on free-induction-decay that observes the spin precession dynamics in-the-dark using Ramsey-like pulses. This aids in suppressing the systematic effects originating from the light-atom interaction during readout, thus vastly improving the accuracy of the magnetometer whilst maintaining a sensitivity that is competitive with previous implementations. This detection technique was implemented further to measure the spin relaxation properties intrinsic to the sensor head, useful in determining the optimal buffer pressure that extends the spin lifetime and improves the sensor's sensitivity performance.This thesis describes the implementation of an optically pumped caesium magnetometer containing a 1:5mm thick microfabricated vapour cell with nitrogen buffer gas, operating in a free-induction-decay configuration. This allows us to monitor the free Larmor precession of the spin coherent Cs atoms by separating the pump and probe phases in the time domain. A single light pulse can sufficiently polarise the atomic sample;however, synchronous modulation of the light field actively drives the precession and maximises the induced spin coherence. Both amplitude- and frequency-modulation have been adopted producing noise floors of 3.4 pT / √Hz and 15.6 pT/√Hz, respectively,within a Nyquist limited bandwidth of 500 Hz in a bias field comparable to the Earth's (~50 μT). We investigate the magnetometers capability in reproducing time-varying magnetic signals under these conditions, including the reconstruction of a 100 pT perturbation using signal averaging.Additionally, we discuss a novel detection mode based on free-induction-decay that observes the spin precession dynamics in-the-dark using Ramsey-like pulses. This aids in suppressing the systematic effects originating from the light-atom interaction during readout, thus vastly improving the accuracy of the magnetometer whilst maintaining a sensitivity that is competitive with previous implementations. This detection technique was implemented further to measure the spin relaxation properties intrinsic to the sensor head, useful in determining the optimal buffer pressure that extends the spin lifetime and improves the sensor's sensitivity performance
Doctor of Philosophy
dissertationI will describe a low-pressure flow-through 129Xe polarizer and report its performance by examining both the output 129Xe and in situ Rb polarization. The 129Xe polarization was made using standard NMR techniques, and the Rb polarization measurement was made using optically detected electron paramagnetic resonance. I compared the results of these measurements to a one-dimensional numerical model of the system. While we qualitatively understand the behavior of the system, the comparison between measurement and model reveals several inadequacies in our understanding of many important physical mechanisms. I will discuss the relevant physics necessary to qualitatively understand the system's behavior and suggest what mechanisms may cause the discrepancies in the modeled and measured behavior. I will demonstrate the utility of this Xe polarizer by measuring xenon's chemical shift dependence on the concentration of Bovine Pancreatic Trypsin Inhibitor (BPTI) and some of its mutants. Mutants Y23A and F45G have measured dependence of 0.56±0.05 ppm/mM and 0.47±0.07 ppm/mM, respectively, which is consistent with relatively strong, manufactured binding sites in the structure. Wild type BPTI has a measured dependence of only 0.15±0.02 ppm/mM, suggesting that there exists no specific binding site to which Xe can bind. Finally, the mutant Y35G has a dependence of 0.10±0.07 ppm/mM. This, with previous data, suggests that a large fraction of solution-phase Y35G does not exist in a conformation that allows Xe access to its binding cavity
Metastability exchange optical pumping of 3He gas up to hundreds of millibars at 4.7 Tesla
Neutron Polarimetry with Polarized 3He for the NPDGamma Experiment
Cold neutrons enable the study of the fundamental interactions of matter in low-energy, low-background experiments that complement the efforts of high-energy particle accelerators. Neutrons possess an intrinsic spin, and the polarization of a beam of neutrons defines the degree to which their spins are oriented in a given direction. The NPDGamma experiment uses a polarized beam of cold neutrons to make a high precision measurement, on the order of one part in 100 million, of the parity-violating asymmetry in the angular distribution of emitted gamma-rays from the capture of polarized neutrons on protons. This asymmetry is a result of the hadronic weak interaction (HWI) and is directly proportional to the long-range, weak interaction modeled by the exchange of a pion between two nucleons. The results of the NPDGamma experiment are dependent on the polarization of the neutron beam used in the capture reaction. The neutron polarization is measured using the large spin-dependent neutron capture cross section of polarized 3He to a precision of less than 2%, which does not significantly increase the total error of the measured gamma-ray asymmetry. Reported here is a description of the NPDGamma experiment, the work done to polarize 3He, and the results of the neutron beam polarimetry measurements
Applications of the Faraday Effect in Hot Atomic Vapours
This thesis presents both a computational and experimental investigation into light propagation in hot alkali-metal vapours, with a particular focus on utilizing the Faraday effect for practical applications. A model to calculate various spectra for a weak-probe laser beam in an atomic medium with an applied axial magnetic field is presented. A computer program (ElecSus) was developed which implements this model efficiently. Using ElecSus we design optical devices such as Faraday filters and laser frequency stabilizing references. The design of Faraday filters utilizing compact vapour cells is shown, along with excellent agreement with experiment. The importance of including the effect of self broadening in the model is shown for these short path length vapour cells. Also, a Faraday filter is presented that can potentially be used for quantum optics experiments on the caesium D line (894~nm). The filter displays the highest ratio of transmission to equivalent noise bandwidth to date for a linear Faraday filter, demonstrating the power of computerized optimization for this application. Furthermore, a Faraday filter is presented for use as an intra-cavity element in an external-cavity diode laser. A proof-of-principle experiment is demonstrated which shows that using a short external cavity with the Faraday filter eliminates mode-hops.
Experimentally and theoretically the Faraday effect is investigated in large magnetic fields where alkali-metal atoms enter the hyperfine Paschen-Back regime. This hyperfine Paschen-Back Faraday effect is shown to allow a direct measure of the refractive indices for left and right circular polarized light. Furthermore, fitting the weak-probe spectra using ElecSus is found to give measures of the magnetic field with a fractional precision of the order of . In addition we study slow-light pulse propagation in a high density rubidium vapour, showing that our theoretical model for the electric susceptibility is valid for short pulses as well as continuous-wave light. This shows that the model is accurate for predicting weak-probe pulse propagation
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