Spin Noise Spectroscopy In Metestable Helium

This Ph.D.thesis mainly addresses the spin noise spectroscopy(SNS)of metastable helium.We report for the first time the measurement of spontaneous spin noise of metastable helium atom ensemble using non-invasive spin noise spectroscopy.We utilize an offresonant laser to investigate the random fluctuations of the Zeeman states of the ground level of metastable helium with a mild magnetic field of approximately 1 Gauss.Moreover,we examine the changes in the spectral pattern when the probe approaches the resonance.We investigate the two main types of polarization noise of the probe,namely Faraday rotation noise and ellipticity noise.To replicate the experimental spin noise signal qualitatively and quantitatively,we construct a simulation model that performs well even near resonance.After the investigation of the simpler level structure of the metastable helium transition line,we extend spin noise spectroscopy to the transition lines with more complicated structures.Our simulation results are consistent with the experimental findings,which are distinct from those obtained using the simpler level structure.To explain the SNS pattern’s characteristics near different transition lines,we have developed a comprehensive theoretical model based on the superposition states theory.We then investigate the correlation between Faraday rotation noise and ellipticity noise.Using the eight noise modes of spin-1,we are able to explain the correlation under different conditions.Additionally,we study the effect of magnetic field noise on the SNS pattern.The magnetic field noise is found to alter the noise spectra pattern,and the eight noise modes theory is able to well explain this phenomenon well.This Ph.D.work mainly serves as proof of principle.The simple level structure of metastable helium provides an ideal model to study the phenomenon of spin noise spectroscopy in spin-1 systems.These findings offer a fresh perspective on SNS and the characterization of spin-1 systems.This new understanding can assist in further research in this area.