  The effects of small relativistic corrections to the off-resonant
polarizability, hyperpolarizability, and second hyperpolarizability are
investigated. Corrections to linear and nonlinear optical coefficients are
demonstrated in the three-level ansatz, which includes corrections to the Kuzyk
limits when scaled to semi-relativistic energies. It is also shown that the
maximum value of the hyperpolarizability is more sensitive than the maximum
polarizability or second hyperpolarizability to lowest-order relativistic
corrections. These corrections illustrate how the intrinsic nonlinear-optical
response is affected at semi-relativistic energies.
