Ultrafast creation and control of population density gratings via ultraslow polarization waves

In the regime of resonant coherent light-matter interaction, light pulses may interact with each other indirectly via a polarization wave created by the other pulse. We show that such interaction allows fast creation and erasing of highcontrast dynamic population density gratings, as well as control of their period in a few-cycle regime. Our scheme uses counter-propagating optical pulses, which do not cross each other in the medium. The mechanism is able to work with pulse durations up to the single-cycle limit. Somewhat surprisingly, ultrafast grating wave vector control requires the generation of polarization waves with the phase velocity much smaller than that of light. (C) 2016 Optical Society of America