  We study theoretically quantum transport through laser-irradiated metallic
atomic-sized contacts. The radiation field is treated classically, assuming its
effect to be the generation of an ac voltage over the contact. We derive an
expression for the dc current and compute the linear conductance in one-atom
thick contacts as a function of the ac frequency, concentrating on the role
played by electronic structure. In particular, we present results for three
materials (Al, Pt, and Au) with very different electronic structures. It is
shown that, depending on the frequency and the metal, the radiation can either
enhance or diminish the conductance. This can be intuitively understood in
terms of the energy dependence of the transmission of the contacts in the
absence of radiation.
