A mid-frequency asymmetric-bipolar pulsed magnetron sputtering system in the frequency range from 100 to 300 kHz has been investigated by a combined application of a Langmuir double probe and optical emission spectroscopy. Both methods have been applied on a time-resolved basis to obtain information about the temporal evolution of the discharge during the pulse. In earlier papers, we have shown by Langmuir probe measurement that a typical two-peak structure of the plasma density at the beginning of the "on" phase occurs which is dependent on the pulse parameters. In this paper, we report on the confirmation of this structure by optical emission spectroscopy which yields a similar structure but with a weaker leading maximum. The studies reveal that the argon emission at 750.4 nm is best suited to monitor temporal changes in the electron density.