  We study the spatial mode content at the output of a wide-field SU(1,1)
interferometer, i.e. a nonlinear interferometer comprising two
coherently-pumped spatially-multimode optical parametric amplifiers placed in
sequence with a focusing element in between. This device is expected to provide
a phase sensitivity below the shot-noise limit for multiple modes over a broad
angular range. To reconstruct the spatial modes and their weights, we implement
a simple method based on the acquisition of only intensity distributions. The
eigenmode decomposition of the field is obtained through the measurement of the
covariance of intensities at different spatial points. We investigate both the
radial and azimuthal (orbital angular momentum) modes and show that their total
number is large enough to enable applications of the interferometer in
spatially-resolved phase measurements.
