A one‐dimensional ballistic constriction has been fabricated from a two‐dimensional electron gas formed at the interface of a GaAs/AlGaAs heterostructure. The constriction was induced via a pair of front gates which also served as a broadband far‐infrared (FIR) antenna. The photocurrent through the constriction was recorded as a function of source‐drain bias at various FIR frequencies, one‐dimensional subband spacings, and for orthogonal FIR polarizations. The photocurrent was compared to the derivative of dc conductance with respect to source‐drain bias. While dc rectification is shown to dominate the photocurrent, deviations from this model occur at frequencies above ∼1 THz, yielding an estimate of the upper limit of the electron scattering time in the constriction region. ©1995 American Institute of Physics.