Photoionization cross sections of ultracold 88Sr in 1P1 and 3S1 states at 390 nm and the resulting blue-detuned magic wavelength optical lattice clock constraints.

We present the measurements of the photoionization cross sections of the excited 1P1 and 3S1 states of ultracold 88Sr atoms at 389.889 nm wavelength, which is the magic wavelength of the 1S0-3P0 clock transition. The photoionization cross section of the 1P1 state is determined from the measured ionization rates of 88Sr in the magneto-optical trap in the 1P1 state to be 2.20(50)×10-20 m2, while the photoionization cross section of 88Sr in the 3S1 state is inferred from the photoionization-induced reduction in the number of atoms transferred through the 3S1 state in an operating optical lattice clock to be 1.38(66) ×10-18 m2. Furthermore, the resulting limitations of employing a blue-detuned magic wavelength optical lattice in strontium optical lattice clocks are evaluated. We estimated photoionization induced loss rates of atoms at 389.889 nm wavelength under typical experimental conditions and made several suggestions on how to mitigate these losses. In particular, the large photoionization induced losses for the 3S1 state would make the use of the 3S1 state in the optical cycle in a blue-detuned optical lattice unfeasible and would instead require the less commonly used 3D1,2 states during the detection part of the optical clock cycle.

Line mixing in the oxygen B band head.

We present the results of direct measurements of the line mixing parameters for two pairs of overlapping transitions at the band head of the oxygen B band. Measurements were performed with the frequency-stabilized cavity ring-down spectrometer assisted by an optical frequency comb. The recorded spectra were analyzed with line profiles comprising speed dependence, Dicke narrowing, and line mixing. Incorporation of the line mixing into the model eliminated previous discrepancies for pressure shift and their speed dependence coefficients. First-order line mixing was determined directly from the line shape fitting at relatively low pressure (0.04 atm) together with other line shape parameters and compared with that calculated by Sung et al. [J. Quant. Spectrosc. Radiat. Transfer 235, 232-243 (2019)].

Dual Hg-Rb magneto-optical trap.

We present a two-species laser cooling apparatus capable of simultaneously collecting Rb and Hg atomic gases into a magneto-optical trap (MOT). The atomic sources, laser system, and vacuum set-up are described. While there is a loss of Rb atoms in the MOT due to photoionization by the Hg cooling laser, we show that it does not prevent simultaneous trapping of Rb and Hg. We also demonstrate interspecies collision-induced losses in the 87Rb-202Hg system.

Pressure and temperature dependencies of air-perturbed O2 B-band line shapes.

The air-broadened lines from the oxygen B band were measured for the first time in controlled laboratory conditions with a high signal-to-noise ratio using frequency-stabilized cavity ring-down spectroscopy (FS-CRDS) referenced to the optical frequency comb. Spectra measured at various pressures and temperatures were analyzed with an advanced line-shape model, considering the speed-dependence of collisional broadening and shift, and the effect of velocity-changing collisions. The temperature dependence of collisional broadening and shift is determined, whereas no significant temperature dependence of speed-dependent parameters and Dicke narrowing was observed. In addition, we have demonstrated that reasonable estimation of temperature dependence for pressure broadening is possible even from measurements done in single temperature where the speed dependence of pressure broadening was determined. New spectroscopic data improve the accuracy of the air-broadened oxygen B-band spectra description by an order of magnitude.