We report on the generation of narrow-bandwidth and frequency-modulated cascaded emission of two photons from a collimated Yb atomic beam. Efficient population transfer from the ground state (
6s2 1S0) to upper state (
6s7s 1S0), of which direct transition at 291.1 nm is dipole forbidden, is achieved through a resonant two-photon excitation enhanced by the electromagnetically induced transparency mediated by the intermediate state (
6s6p 1P1). Then cascaded emission of two photons with a bandwidth of 54 MHz at 611.3 nm (idler) and 555.8 nm (signal) occurs in sequence from the upper state via the spin triplet state (
6s2 3P1). Numerical calculations of the density matrix equations taking into account the residual Doppler effect and strong driving fields successfully explain the experimental results for the idler and signal beam intensities depending on the various parameters of the driving fields. Synchronized optical switching and frequency-modulation characteristics of the idler and signal beams are also reported.
We calculate and measure the magic wavelengths for the $6{s}^{2}^{1}S_{0}\ensuremath{-}6s6p\phantom{\rule{0.16em}{0ex}}^{3}P_{1}$ intercombination transition of the neutral ytterbium atom. The calculation is performed with the ab initio configuration interaction
+ all-order method. The measurement is done with laser spectroscopy on cold atoms in an optical dipole trap. The magic wavelengths are determined to be 1035.68(4) nm for the $\ensuremath{\pi}$ transition $(\mathrm{\ensuremath{\Delta}}m=0)$ and 1036.12(3) nm for the $\ensuremath{\sigma}$ transitions $(|\mathrm{\ensuremath{\Delta}}m|=1)$ in agreement with the calculated values. Laser cooling on the narrow intercombination transition could achieve better results for atoms in an optical dipole trap when the trap wavelength is tuned to near the magic wavelength.
We report the magneto-optical trapping of ytterbium atoms using the ${6s}^{2}{}^{1}{S}_{0}\ensuremath{-}6s6p{}^{3}{P}_{1}$ intercombination transition. The magneto-optical trap is continuously loaded from an atomic beam decelerated by a Zeeman-tuned atomic-beam slower operated at the ${6s}^{2}{}^{1}{S}_{0}\ensuremath{-}6s6p{}^{1}{P}_{1}$ transition. Among seven stable isotopes of ytterbium, six isotopes
of170Yb, 171Yb, 172Yb, 173Yb, 174Yb, and
176Yb are successfully trapped. The number and density of the trapped atoms are about
108 and ${10}^{11} {\mathrm{cm}}^{\ensuremath{-}3},$ respectively. The temperature of atoms is estimated to be about $20 \ensuremath{\mu}\mathrm{K}$ from the time-of-flight measurement. The decay time of the trapped atoms after stopping the loading of atoms is about 3 s.
We demonstrate launching of laser-cooled Yb atoms in a cold atomic fountain. Atoms in a collimated thermal beam are first cooled and captured in a magneto-optical trap (MOT) operating on the strongly allowed ${{}^{1}S}_{0}\ensuremath{\rightarrow}{{}^{1}P}_{1}$ transition at 399 nm (blue line). They are then transferred to a MOT on the weakly allowed ${{}^{1}S}_{0}\ensuremath{\rightarrow}{{}^{3}P}_{1}$ transition at 556 nm (green line). Cold atoms from the green MOT are launched against gravity at a velocity of around 2.5 m/s using a pair of green beams. We trap more than
107 atoms in the blue MOT and transfer up to
70 into the green MOT. The temperature for the odd isotope
171Yb is
1mK in the blue MOT, and reduces by a factor of 40 in the green MOT.
Here we report atomic structure calculations and experimental observations of the two-photon
6s21S0→6s23s1S0 transition in Yb. The unique level structure of Yb places the
6s6p1P1 state's energy at
≈49.7% of the ionization energy, which facilitates two-photon Doppler-free excitation of the
6s23s1S0 Rydberg state from the
6s21S0 ground state at a relatively low optical intensity. This
J=0→J=0 transition is immune to first-order Zeeman and electric quadrupole shifts, has reduced sensitivity to higher-order Zeeman shifts, and is further predicted to have relatively low sensitivity to density shifts. Using configuration interaction theory, we compute relevant properties of the
6s23s1S0 Rydberg state for sensing, including the
C6 coefficient, dc polarizability, blackbody radiation (BBR) shift, and BBR depopulation rate. As a first experimental step, we demonstrate two-photon Doppler-free spectroscopy of the
6s21S0→6s23s1S0 transition. From our experimental spectra, we estimate the natural linewidth (lifetime) of the
6s23s1S0 state to be 90 kHz (1.8
μs). We believe this transition, or other
6s21S0→6sns1S0 transitions in Yb with
n≈23, may find use in a variety of sensing applications, potentially including a two-photon clock, electrometer, or BBR thermometer.
We report the magneto-optical trapping of ytterbium atoms using the 6s2 1S0-6s6p 3P1 intercombination transition. The magneto-optical trap is continuously loaded from an atomic beam decelerated by a Zeeman-tuned atomic-beam slower operated at the 6s2 1S0-6s6p 1P1 transition. Among seven stable isotopes of ytterbium, six isotopes of 170Yb, 171Yb, 172Yb, 173Yb, 174Yb, and 176Yb are successfully trapped. The number and density of the trapped atoms are about 108 and 1011 cm-3, respectively. The temperature of atoms is estimated to be about 20 μK from the time-of-flight measurement. The decay time of the trapped atoms after stopping the loading of atoms is about 3 s.