Study of CPO resonances on the intercombination line in $^{173}$Yb

TL;DR

This study investigates coherent population oscillations in the $^{173}$Yb isotope, demonstrating linewidth narrowing from over 190 kHz to about 100 kHz through magnetic field application and sublevel coherence effects.

Contribution

It provides new insights into CPO behavior in $^{173}$Yb, highlighting how magnetic fields and hyperfine structure influence linewidth and coherence.

Findings

Linewidth reduced from 190 kHz to 100 kHz with magnetic field.

Formation of two M-type systems under magnetic field.

Spin coherence limits fluorescence in the presence of a magnetic field.

Abstract

We study coherent population oscillations (CPO) in an odd isotope of the two-electron atom Yb. The experiments are done using magnetic sublevels of the $ F_g = 5/2 \rightarrow F_e = 3/2 $ hyperfine transition in $^{173}$Yb of the $ {\rm {^1S_0} \rightarrow {^3P_1}} $ intercombination line. The experiments are done both with and without an appied magnetic field. In the absence of an applied field, the complicated sublevel structure along with the saturated fluorescence effect causes the linewidth to be larger than the 190 kHz natural linewidth of the transition. In the presence of a field (of magnitude 330 mG), a well-defined quantization axis is present which results in the formation of two M-type systems. The total fluorescence is then limited by spin coherence among the ground sublevels. In addition, the pump beam gets detuned from resonance which results in a reduced scattering rate from the $ {\rm ^3P_1} $ state. Both of these effects result in a reduction of the linewidth to a subnatural value of about 100 kHz.