  Counter-propagating and suitably polarized light (laser) beams can provide
conditions for pair production. Here, we consider in more detail the following
two situations: (i) In the homogeneity regions of anti-nodes of linearly
polarized ultra-high intensity laser beams, the Schwinger process is
dynamically assisted by a second high-frequency field, e.g. by a XFEL beam.
(ii) A high-energy probe photon beam colliding with a superposition of
co-propagating intense laser and XFEL beams gives rise to the laser assisted
Breit-Wheeler process. Prospects of such bi-frequent field constellations with
respect to the feasibility of conversion of light into matter are discussed.
