  We present mirror and beamsplitter pulse designs that improve the fidelity of
atom interferometry and increase its tolerance of systematic inhomogeneities.
These designs are demonstrated experimentally with a cold thermal sample of
$^{85}$Rb atoms. We first show a stimulated Raman inversion pulse design that
achieves a ground hyperfine state transfer efficiency of 99.8(3)%, compared
with a conventional $\pi$ pulse efficiency of 75(3)%. This inversion pulse is
robust to variations in laser intensity and detuning, maintaining a transfer
efficiency of 90% at detunings for which the $\pi$ pulse fidelity is below 20%,
and is thus suitable for large momentum transfer interferometers using thermal
atoms or operating in non-ideal environments. We then extend our optimization
to all components of a Mach-Zehnder atom interferometer sequence and show that
with a highly inhomogeneous atomic sample the fringe visibility is increased
threefold over that using conventional $\pi$ and $\pi/2$ pulses.
