  An influence of pass-through optics on femtosecond laser pulse filamentation
in ambient air is analyzed for the first time both experimentally and
numerically. Propagation of high-power femtosecond laser pulse through solid
optical elements introduces spatiotemporal phase modulation due to the Kerr
effect. This modulation may have a strong ef-fect on the pulse filamentation in
air. We demonstrated that the phase modulation obtained in the thin
pass-through dielectric plate reduces the distance to the filament onset and
increases the plasma channel length
