Detecting presence or absence of plasma is accomplished from probe signals. In one embodiment, a low-power modulated signal is applied to an electrostatic chuck from a bias power generator. A corresponding system then monitors peak-to-peak voltage (Vpp) signal responses or radio frequency current responses. The probe signal can be generated to have insufficient power to either ignite or sustain plasma discharge (or cause component damage). Thus, low-duty and/or low current pulsing signals to be used. Presence or absence of the bulk plasma will then result in different Vpp or radio frequency current values.