  We formulate the spin contribution to the inverse Faraday effect of
non-magnetic metals. We deal with the role of the inversion symmetry, which
forces all electronic bands to be at least twice degenerate at every point in
the Brillouin zone. We show both analytically and numerically that our
formulation of the inverse Faraday effect is invariant under unitary rotation
within the doubly degenerate set of bands. In addition, we show the importance
of resonance-like features in the band structure for the inverse Faraday
effect. Our first-principles computed spin component of the inverse Faraday
effect in a simple metal such as Au is reminiscent of its optical absorption,
with a characteristic d-s resonance in the optical spectrum.
