  Production of electron-positron pairs from vacuum in strong bichromatic
electric fields, oscillating in time with a fundamental frequency and its
second harmonic, is studied. Strong-field processes occuring in such field
configurations are generally known to be sensitive to the relative phase
between the field modes. Phase-of-the-phase spectroscopy has recently been
introduced in the context of strong-field photoionization as a systematic means
to analyze these coherence effects. We apply this method to field-induced pair
production by calculating the phase dependence of the momentum-resolved
particle yields. We show that asymmetric checkerboard patterns arise in the
phase-of-the-phase spectra, similarly to those found in strong-field
photoionization. The physical origin of these characteristic structures, which
differ between the created electron and positron, are discussed.
