  Waveform-controlled Terahertz (THz) radiation is of great importance due to
its potential application in THz sensing and coherent control of quantum
systems. We demonstrated a novel scheme to generate waveform-controlled THz
radiation from air plasma produced when carrier-envelope-phase (CEP) stabilized
few-cycle laser pulses undergo filamentation in ambient air. We launched
CEP-stabilized 10 fs-long (~ 1.7 optical cycles) laser pulses at 1.8 {\mu}m
into air and found that the generated THz waveform can be controlled by varying
the filament length and the CEP of driving laser pulses. Calculations using the
photocurrent model and including the propagation effects well reproduce the
experimental results, and the origins of various phase shifts in the filament
are elucidated.
