Studying Double Resonance Optical Pumping Effects in Thallium 6P1/2→6P3/2 Forbidden Transitions with Amplitude- and Phase-Modulated Absorption Spectroscopy
Wei-Ling, Chen1*, Tzu-Ling, Chen1, Yi-Wei, Liu1
1Department of Physics, National Tsing Hua University, Hsinchu, Taiwan
* presenting author:WEI-LING CHEN,
Forbidden transitions in heavy atoms are used to study atomic parity non-conservation (PNC) effect by observing optical rotation, which is due to the mixing of PNC induced E1 transition and original M1 transition. The 6P1/2→6P3/2 of thallium (Tl) at 1.283 μm is such an important transition. Tl, with its three valence electrons, is the second simplest atom (after Cs) for which the PNC has been observed experimentally.
Here we proposed to measure the transition involved with possible PNC effect by simultaneously stimulating the M1 or E2 transitions within Tl hyperfine structure. With a tunable external cavity diode laser centered at 1.283 μm and a EOM modulated at the frequency of half of low-lying hyperfine splitting (HFS, ~21 GHz), a Λ-type system can be driven by the laser field formed by the two sidebands generated by the EOM.
In this report, we present the absorption spectroscopy of the resonances from two hyperfine forbidden transitions of Tl 6P1/2→6P3/2 in a 10 cm long vapor cell. By tuning the laser frequency, the interactions between the two transitions are observed at varied value of frequency modulation. By implanting amplitude modulation in frequency modulated light to reduce noises, the signal can be detected at a relative low temperature, where the resonances undergo less pressure broadening and Doppler broadening. The spectroscopic results can be used for systematical study of the atomic structure. Furthermore, we hope some kind of quantum interference features, such as electromagnetically induced transparency (EIT), can be observed when the modulation frequency matches to half of HFS. Then the intrinsic PNC effect could be possibly resolved based on the further results.

Keywords: thallium, absorption spectroscopy, forbidden transitions