Potassium tune-out-wavelength measurement using atom interferometry and a multipass optical cavity

The longest tune-out wavelength for potassium atoms, lambda(zero) = 768.9701(4) nm, was measured using an atom interferometer with a large irradiance gradient supported in a multipass optical cavity. Systematic errors in lambda(zero) measurements that arise from laser light, Doppler shifts, and the Earth's rotation are described. The ratio of oscillator strengths for the potassium D2 and D1 lines inferred from this lambda(zero) measurement is rho = f(D2)/f(D1) = 2.0066(11), and the ratio of line strengths is R = S-D2/S-D1 = 1.9977(11).