Steering low-energy photoelectrons using orthogonal mid-infrared and VUV fields

Multiphoton ionization driven by combined mid-infrared (MIR) and vacuum-ultraviolet (VUV) fields can proceed efficiently even when the VUV photon energy lies below the ionization threshold, provided that additional MIR photons bridge the energy gap. When using a few-cycle MIR pulse, its large bandwidth enables a two-color regime in which two distinct ionization pathways, which differ by one absorbed MIR photon, reach the same final photoelectron energy and therefore interfere coherently. Using the hydrogen atom as a example and solving the time-dependent Schr\"{o}dinger equation in the combined fields, we show that the total ionization yield exhibits a pronounced phase-delay dependence, oscillating twice per MIR optical cycle as the relative MIR-VUV phase is varied. This sub-cycle modulation is a direct signature of interference between the competing multiphoton pathways. In an orthogonal-field geometry, the same pathway interference imprints a strong, phase-dependent modulation on the low-energy photoelectron momentum distribution, enabling substantial redistribution and redirection of emitted photoelectrons. These results establish a new coherent-control scheme for steering photoelectrons via interference of multiphoton pathways in two-color strong-field ionization, and provide a simple platform for extending phase-controlled electron shaping to more complex targets.