High-resolution two-photon spectroscopy of a $5p^{5}6p\leftarrow 5p^6$ transition of xenon

We report high-resolution Doppler-free two-photon excitation spectroscopy of Xe from the ground state to the $5p^5\left({}^{2}P_{3/2}\right)6p{}^2[3/2]_2$ electronic excited state. This is a first step to developing a comagnetometer using polarized ${}^{129}\mathrm{Xe}$ atoms for planned neutron electric dipole moment measurements at TRIUMF. Narrow linewidth radiation at 252.5 nm produced by a continuous wave laser was built up in an optical cavity to excite the two-photon transition, and the near-infrared emission from the $5p^{5}6p$ excited state to the $5p^{5}6s$ intermediate electronic state was used to detect the two-photon transition. Hyperfine constants and isotope shift parameters were evaluated and compared with previously reported values. In addition, the detected photon count rate was estimated from the observed intensities.

Figure 1

Experimental setup of the UV enhancement cavity in the vacuum chamber, backfilled with Xe and ${\mathrm{O}}_2$ gas. The cavity is made with two curved mirrors, an input coupler (IC) and high reflector (HR), each with radius of curvature = 150 mm and separated by 260 mm. L1 and L2 are lenses for mode matching the UV light into the enhancement cavity. A quarter wave plate ($\lambda$/4), a polarized beam splitter (PBS) and a piezoelectric transducer (PZT) are used to lock the UV cavity. We collect fluorescence perpendicular to the beam at the focus of the cavity using two 1 in diameter lenses, L3 and L4, with focal lengths 19 mm and 50 mm, respectively. The light is focused onto an APD placed outside the vacuum chamber. A power meter monitors the circulating UV power. Inset: relevant energy levels corresponding to the two-photon transition and LIF under investigation.

Figure 2

Excitation spectrum of natural abundance Xe. The total pressure was 1.6 Torr, with a 50:50 ratio of Xe and ${\mathrm{O}}_2$. The $x$ axis corresponds to the Xe transition frequency, eight times larger than the OPSL frequency. The $y$ axis is the observed LIF intensity of the combined 895 nm and 823 nm emission. The peaks are shown with the fitted Lorentzian line shape as described in the text. Each peak is labeled with its mass number; additionally, odd isotopes are labeled with their excited state hyperfine level $F$ in parentheses. The stick diagram shows the calculated peak positions and intensities obtained from the Lorentzian fit.

Figure 3

Calculated field shifts vs $\delta \langle r^2\rangle$ for three published data sets [13, 23, 24]. Inset: residuals from the linear fit are smallest for Borchers' data.