  The Raman response in the antiferromagnetic 2-leg S=1/2 Heisenberg ladder is
calculated for various couplings by continuous unitary transformations. For leg
couplings above 80% of the rung coupling a characteristic 2-peak structure
occurs with a point of zero intensity within the continuum. Experimental data
for CaV_2O_5 and La_yCa_(14-y)Cu_24O_41 are analyzed and the coupling constants
are determined. Evidence is found that the Heisenberg model is not sufficient
to describe cuprate ladders. We argue that a cyclic exchange term is the
appropriate extension.

Strongly Correlated Electrons;Superconductivity