  Inclusive double differential multiplicities of deuterons, ^3H, ^3He, and
^4He measured by E877 for 11.5 A GeV/c Au+Au collisions at the AGS are
presented. Light fragments at beam-rapidity are measured for the first time at
AGS energies. Beam rapidity deuteron and ^4He yields and transverse slope
parameters are found to be strongly dependent on impact parameter and the shape
of the deuteron spectra is not consistent with that expected for a simple
thermal distribution. The deuteron yields relative to proton yields are
analyzed in terms of a simple coalescence model. While results indicate an
increase in source size compared to collisions of lighter systems at the same
energy, they are inconsistent with a simple coalescence model reflected by a
rapidity dependence of the coalescence parameter B_d. A new approach utilizing
an expanding thermalized source combined with a coalescence code is developed
for studying deuteronformation in heavy-ion collisions. The strong dependence
of deuteron yields on collective motion implies that deuteron yields relative
to those of protons can be used for constraining source parameters.
