  We propose a realistic scheme to detect topological edge states in an optical
lattice subjected to a synthetic magnetic field, based on a generalization of
Bragg spectroscopy sensitive to angular momentum. We demonstrate that using a
well-designed laser probe, the Bragg spectra provide an unambiguous signature
of the topological edge states that establishes their chiral nature. This
signature is present for a variety of boundaries, from a hard wall to a smooth
harmonic potential added on top of the optical lattice. Experimentally, the
Bragg signal should be very weak. To make it detectable, we introduce a
"shelving method", based on Raman transitions, which transfers angular momentum
and changes the internal atomic state simultaneously. This scheme allows to
detect the weak signal from the selected edge states on a dark background, and
drastically improves the detectivity. It also leads to the possibility to
directly visualize the topological edge states, using in situ imaging, offering
a unique and instructive view on topological insulating phases.
