  The twisted Gaussian Schell Model describes a family of partially coherent
beams that present several interesting characteristics, and as such have
attracted attention in classical and quantum optics. Recent techniques have
been demonstrated to synthesize these beams from a coherent source using a
discrete set of "pseudo-modes", where the phase of each mode is randomized so
that they are mutually incoherent. Here we investigate this technique and
evaluate the resulting beam parameters, such as divergence, coherence length
and twist phase. We show that for a finite set of modes there is also some
residual coherence, which can have an observable effect. A theoretical model is
developed for the output field that includes residual coherence and agrees very
well with experimental data. In addition, we demonstrate a simple method to
measure the twist phase using double slit interference.
