where Ên are polarizations of the laser pulses (which are determined by the experimental setup) and μα are the transition dipole moments. The angles θ ab (with latin letters) are angles between the laser pulses, whereas θ αβ (with greek letters) are angles between transition dipole moments. The specific combination of transition dipole moments relevant for each of the six response functions is given by the subscripts of ⟨C α,β,γ,δ ⟩ in Eqs. (17) to (22), where single indices i, j, k refer to transitions from the ground state to the specified excited state, and double indices ik and jk refer to the transition from the singly-excited state i or j to the doubly excited state k.