  We have demonstrated a new technique that provides massively parallel comb
spectroscopy sensitive specifically to ions through the combination of
cavity-enhanced direct frequency comb spectroscopy with velocity modulation
spectroscopy. Using this novel system, we have measured electronic transitions
of HfF+ and achieved a fractional absorption sensitivity of 3 x 10-7 recorded
over 1500 simultaneous channels spanning 150 cm-1 around 800 nm with an
absolute frequency accuracy of 30 MHz (0.001 cm-1). A fully sampled spectrum
consisting of interleaved measurements is acquired in 30 minutes.
