Variation of Spectral Content of Subcycle Far-Infrared Pulses Due to Phase-Amplitude Modulation in Near-Field Diffraction

Spectral content of subcycle electromagnetic pulses is not conserved under phase shift of the carrier oscillations with respect to the pulse enevelope. We observe carrier phase dependent large variation of the low frequency content of subcycle far-infrared (terahertz) pulses in the near-field zone of a subwavelength aperture.