[en] Current fluctuations in ballistic quantum point contacts attract now much attention, both in theory and experiment partly because of the assumed possibility to measure fractional charges in shot-noise and to probe other non Fermi liquid properties. We are interested in current fluctuations in a ballistic point contacts biased by applied voltage and irradiated by external field. Time averaged current in microstructures under such conditions (photon-assisted current) was investigated experimentally in point contacts and quantum dots. We consider a classical field which can be coherent (e.g. microwave radiation) or incoherent (e.g. representing the environment at high enough temperature or a heat phonon pulse). We assume that the field does not irradiate the leads between which the bias is applied. Which means e.g. modulated gate voltage, not modulated bias voltage. We model this situation considering a 1D channel with a time-dependent barrier potential U(x, t). The d.c. part of the potential U₀(x) is due to the squeezing of the point contacts while the a.c. part JδU(x, t) is due to the field. We suggest a new approach to calculate current and current correlations in such a system. The approach is based on the concept of scattering states for a time dependent Hamiltonian. Consider the 1D Schroedinger equation i(∂/∂_t)ψ = Hψ for one particle with a time dependent Hamiltonian H = -∇²/2m + U(x,t), where the barrier potential U(x,t) = 0 at x->→ ±∞ for all t. For any energy ε_k ≡ k²/2m > 0 (with k > 0) we define time dependent scattering states Χ^σ_k(x,t),σ = ±, as solutions of the Schroedinger equation with the following boundary conditions: the only incoming waves are e^-iε_kt+ikx for Χ⁺_k e^-iε_kt-ikx for Χ^-_k. The outgoing parts of Χ⁺_k contain waves with k' ≠ k, describing inelastic scattering in transmission and reflection by the a.c. barrier. The time-dependent electron field operator can be calculated in the following way: Ψ(x,t) Σ_kσσ^σ_kΧ^σ_k(x,t), where σσ^σ_k are Fermi operators of electrons in the left lead and the right lead at x = ±∞, respectively. Electrons in different leads do not correlate, while averages for operators belonging to the same lead can be calculated as for a free Fermi gas with chemical potentials μ^± introducing the bias voltage V = (μ₊ - μ_-)/e. Using this approach we calculated the spectra of the current noise in a biased contact irradiated by a weak random field. Considered examples demonstrate that the nonequilibrium noise excited by irradiation differs essentially from nonequilibrium noise excited by bias