  We show that dark solitons in 1D Bose liquids may be created by absorption of
a single quanta of an external ac field, in a close analogy with the Einstein's
photoelectric effect. Similarly to the von Lenard's experiment with
photoexcited electrons, the external field's photon energy $\hbar\omega$ should
exceed a certain threshold. In our case the latter is given by the soliton
energy $\varepsilon_s(\hbar q)$ with the momentum $\hbar q$, where $q$ is
photon's wavenumber. We find the probability of soliton creation to have a
power-law dependence on the frequency detuning $\omega-\varepsilon_s/\hbar$.
This dependence is a signature of the quantum nature of the absorption process
and the orthogonality catastrophe phenomenon associated with it.
