Browsing by Author "She, C. Y., advisor"

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Open Access
Detection and transit time measurements of individual sodium atoms diffusing in a helium flow by the laser resonance fluorescence correlation technique
(Colorado State University. Libraries, 1979) Pan, Ci-Ling, author; She, C. Y., advisor
This thesis describes the laser resonance fluorescence correlation technique for single-atom velocity measurement. Using this technique, we have detected individual sodium atoms diffusing through a laser beam in a slow helium flow. From the width of the fluorescence bursts detected, the transit time for the diffusing atom is determined. This is the first measurement of the motion of a single atom in a buffer gas. A probability analysis was developed which allowed us to estimate the average burst size of emitted fluorescence photons by an atom traversing the laser beam. All these results were in general agreement with the theoretical predictions. With improvements, we will be able to measure the velocity of a single-atom either in a flow or in a vacuum. By averaging over many sodium atoms, the diffusion coefficients of sodium atoms in helium and argon buffer gases were investigated using this technique. The measured diffusion coefficients were found to be in reasonable agreement with theoretical predictions and previous experimental results. To our knowledge, this is the first application of resonance fluorescence correlation technique to the measurement of diffusion coefficient of fast moving atoms in gases.
Open Access
Raman studies in NH₄H₂PO₄ and KH₂PO₄
(Colorado State University. Libraries, 1972-01) Broberg, Theodore Waldo, author; She, C. Y., advisor; Edwards, David F., advisor; Krueger, David A., committee member; Raich, J. C., committee member
Laser Raman spectra for NH4H2PO4 (ADP) and KH2PO4 (KDP) are presented as a function of temperature in the region above the phase transitions. Evidence is presented confirming the existance of strong coupling between the proton B2 tunneling mode and the B2 optical phonon mode in both crystals. The spectra were fit to a coupled oscillator function and the relevant fitting parameters are presented. The Debye relaxation time and soft mode frequency for the overdamped mode as well as the static dielectric susceptibility are plotted as a function of temperature. Soft mode behavior in both crystals displays the ω2 α(T-Tc') dependence. For KDP Tc' was determined to be 30°K. Room temperature spectra are presented for KDP and ADP, and five of the six optical phonon modes are identified. The (PO4)3- ion modes are observed to split under the local crystalline field of S4 symmetry and a librational mode of the (NH4)+ ion is resolved.