  Laser assisted photoemission by a chirped subfemtosecond extreme ultraviolet
(XUV) pulse is considered within an exactly solvable quantum-mechanical model.
Special emphasis is given to the energy dependence of photoexcitation
cross-section. The streaked spectra are analyzed within the classical picture
of initial time-momentum distribution r_ini(p,t) of photoelectrons mapped to
the final energy scale. The actual time-momentum distribution in the absence of
the probe laser field is shown to be a poor choice for r_ini, and a more
adequate ansatz is suggested. The semiclassical theory offers a simple
practically useful approximation for streaked spectra. Its limitations for
sufficiently long chirped XUV pulses are established.
