Magic wavelengths near 800 nm for precision spectroscopy of an inner-shell transition in thulium atoms

Differential dynamic polarisability of the inner-shell clock transition at a wavelength of 1.14 μm in the thulium atom is measured by the method of precision laser spectroscopy in the spectral range of 800–860 nm. Experimental data approximated by a theoretical model yield the probability of the transition at λ = 809.5 nm: A_809.5 = 460(70) s^-1. The values of two magic wavelengths are obtained experimentally, namely, λ_m1 = 807.727(18) nm and λ_m2 = 813.3(2) nm, the wavelength of λ_m1 being determined for the first time. Main parameters of an optical lattice at these wavelengths are compared and a conclusion is made that trapping thulium atoms in an optical lattice at λ_m2 is preferable for optical clock operation.