Photoionization cross sections of ultracold Sr in P and S 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 P and S states of ultracold Sr atoms at 389.889 nm wavelength, which is the magic wavelength of the S-P clock transition. The photoionization cross section of the P state is determined from the measured ionization rates of Sr in the magneto-optical trap in the P state to be 2.

Dark resonance formation with magnetically induced transitions: extension of spectral range and giant circular dichroism.

Dark resonances were formed via electromagnetically induced transparency for the first time, to the best of our knowledge, involving magnetically induced ΔF=±2 atomic transitions of alkali metal atoms, which are forbidden at zero magnetic field. The probability of these transitions undergoes rapid growth when 300-3000 G magnetic field is applied, allowing formation of dark resonances, widely tunable in the GHz range. It is established that for ΔF=+2 (ΔF=-2) transition, the coupling laser tuned to ΔF=+1 (ΔF=-1) transition of the hyperfine Λ-system must be σ (σ) polarized, manifesting anomalous circular dichroism.