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Studies of Coherence Narrowing and Resonance Broadening and Effects of Rare Gas on these Phenomena by Zero-Field Level Crossing Spectroscopy in the 7S-STATE of Thallium.

Ching-Chiang . Hsieh

Published Jan 1, 1970• 0 citations
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Level-Crossing Spectroscopy in 7S2 Thallium. I. Studies of Coherence-Narrowing, Collision-Broadening, and Buffer-Gas Effects

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The lifetime, coherence narrowing, and collision broadening of the $7^{2}S_{\frac{1}{2}}$ excited state of atomic thallium has been studied by the technique of zero-field level-crossing spectroscopy. The lifetime of the $7^{2}S_{\frac{1}{2}}$ state is determined to be 7.55 (0.08) nsec. The full coherence-narrowing effect gave a branching ratio, from $F=0$ of $7^{2}S_{\frac{1}{2}}$ to the ground state, of 43%. The cross section for thallium-thallium resonance-broadening collisions is ${\ensuremath{\sigma}}_{\mathrm{T}\mathrm{l}\ensuremath{-}\mathrm{T}\mathrm{l}}=\frac{5.38(0.49)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}}{\overline{v}}$ ${\mathrm{cm}}^{2}$. The effect of 426-torr helium on the thallium lifetime, coherence narrowing, and resonance broadening was also investigated. From the low-thallium-density region the cross section for helium depolarization of the thallium $7^{2}S$ state is ${\ensuremath{\sigma}}_{\mathrm{T}\mathrm{l}\ensuremath{-}\mathrm{H}\mathrm{e}}\ensuremath{\cong}\frac{7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}13}}{\overline{v}}$ ${\mathrm{cm}}^{2}$. There is also indication of a buildup of population in the metastable $6^{2}P_{\frac{3}{2}}$ thallium state. From the data, the cross section for the process $\mathrm{Tl}(6^{2}P_{\frac{3}{2}})\ensuremath{\rightarrow}\mathrm{Tl}(6^{2}P_{\frac{1}{2}})$ by helium collisions is $\ensuremath{\sigma}\ensuremath{\simeq}1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}21}$ ${\mathrm{cm}}^{2}$. The Tl branching ratio in the presence of helium is 39%. It was also found that the thallium-thallium resonance-broadening cross section is ${\ensuremath{\sigma}}_{\mathrm{T}\mathrm{l}\ensuremath{-}\mathrm{T}\mathrm{l}}=\frac{4.04(0.32)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}}{\overline{v}}$ ${\mathrm{cm}}^{2}$ in the presence of 426 torr of helium. In the presence of 113 torr of He, the resonance-broadening cross section was found to be ${\ensuremath{\sigma}}_{\mathrm{T}\mathrm{l}\ensuremath{-}\mathrm{T}\mathrm{l}}=\frac{5.22(0.13)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}}{\overline{v}}$ ${\mathrm{cm}}^{2}$. In the case of Ar as the buffer gas, ${\ensuremath{\sigma}}_{\mathrm{T}\mathrm{l}\ensuremath{-}\mathrm{A}\mathrm{r}}=\frac{8\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}13}}{\overline{v}}$ ${\mathrm{cm}}^{2}$.

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I. INTRODUCTION A. Level-Crossing Phenomena and the Effect of Coherent Forward Scattering Coherent forward.scattering (CFS—used for the physical effect as well as for the approach of coherent forward scattering spectroscopy) has been investigated first in connection with atomic resonance radiation phenomena like double resonance and level-crossing effects.1 The very early level crossing has been measured in lateral fluorescence in a weak magnetic field.2 This “zero-field level crossing” in lateral detected resonance fluorescence is called “Hanle effect”3 and can be classically described by the model of an atomic oscillator, emitting during its Larmor precession with respect to the applied magnetic field (Figure 1).

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Rare-gas-induced broadening and shift of two-photon transitions to intermediate (n=9−14)\mathsf{(n=9{-}14)}(n=9−14) Rydberg states of atomic thallium *
The lifetime, coherence narrowing, and collision broadening of the 72S127^{2}S_{\frac{1}{2}}72S21​​ excited state of atomic thallium has been studied by the technique of zero-field level-crossing spectroscopy. The lifetime of the 72S127^{2}S_{\frac{1}{2}}72S21​​ state is determined to be 7.55 (0.08) nsec. The full coherence-narrowing effect gave a branching ratio, from F=0F=0F=0 of 72S127^{2}S_{\frac{1}{2}}72S21​​ to the ground state, of 43%. The cross section for thallium-thallium resonance-broadening collisions is ${\ensuremath{\sigma}}_{\mathrm{T}\mathrm{l}\ensuremath{-}\mathrm{T}\mathrm{l}}=\frac{5.38(0.49)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}}{\overline{v}}$ cm2{\mathrm{cm}}^{2}cm2. The effect of 426-torr helium on the thallium lifetime, coherence narrowing, and resonance broadening was also investigated. From the low-thallium-density region the cross section for helium depolarization of the thallium 72S7^{2}S72S state is ${\ensuremath{\sigma}}_{\mathrm{T}\mathrm{l}\ensuremath{-}\mathrm{H}\mathrm{e}}\ensuremath{\cong}\frac{7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}13}}{\overline{v}}$ cm2{\mathrm{cm}}^{2}cm2. There is also indication of a buildup of population in the metastable 62P326^{2}P_{\frac{3}{2}}62P23​​ thallium state. From the data, the cross section for the process $\mathrm{Tl}(6^{2}P_{\frac{3}{2}})\ensuremath{\rightarrow}\mathrm{Tl}(6^{2}P_{\frac{1}{2}})$ by helium collisions is $\ensuremath{\sigma}\ensuremath{\simeq}1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}21}$ cm2{\mathrm{cm}}^{2}cm2. The Tl branching ratio in the presence of helium is 39%. It was also found that the thallium-thallium resonance-broadening cross section is ${\ensuremath{\sigma}}_{\mathrm{T}\mathrm{l}\ensuremath{-}\mathrm{T}\mathrm{l}}=\frac{4.04(0.32)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}}{\overline{v}}$ cm2{\mathrm{cm}}^{2}cm2 in the presence of 426 torr of helium. In the presence of 113 torr of He, the resonance-broadening cross section was found to be ${\ensuremath{\sigma}}_{\mathrm{T}\mathrm{l}\ensuremath{-}\mathrm{T}\mathrm{l}}=\frac{5.22(0.13)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}}{\overline{v}}$ cm2{\mathrm{cm}}^{2}cm2. In the case of Ar as the buffer gas, ${\ensuremath{\sigma}}_{\mathrm{T}\mathrm{l}\ensuremath{-}\mathrm{A}\mathrm{r}}=\frac{8\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}13}}{\overline{v}}$ cm2{\mathrm{cm}}^{2}cm2.
I. INTRODUCTION A. Level-Crossing Phenomena and the Effect of Coherent Forward Scattering Coherent forward.scattering (CFS—used for the physical effect as well as for the approach of coherent forward scattering spectroscopy) has been investigated first in connection with atomic resonance radiation phenomena like double resonance and level-crossing effects.1 The very early level crossing has been measured in lateral fluorescence in a weak magnetic field.2 This “zero-field level crossing” in lateral detected resonance fluorescence is called “Hanle effect”3 and can be classically described by the model of an atomic oscillator, emitting during its Larmor precession with respect to the applied magnetic field (Figure 1).