  We measure spectrally and spatially resolved high-order harmonics generated
in argon using chirped multi-cycle laser pulses. Using a stable,
high-repetition rate laser we observe detailed interference structures in the
far-field. The structures are of two kinds; off-axis interference from the long
trajectory only and on-axis interference including the short and long
trajectories. The former is readily visible in the far-field spectrum,
modulating both the spectral and spatial profile. To access the latter, we vary
the chirp of the fundamental, imparting different phases on the different
trajectories, thereby changing their relative phase. Using this method together
with an analytical model, we are able to explain the on-axis behaviour and
access the dipole phase parameters for the short (\(\alpha_s\)) and long
(\(\alpha_l\)) trajectories. The extracted results compare very well with phase
parameters calculated by solving the time-dependent Schr\"odinger equation.
Going beyond the analytical model, we are also able to successfully reproduce
the off-axis interference structure.
