Split-step wave-optical simulations are useful for studying optical
propagation through random media like atmospheric turbulence. The
standard method involves alternating steps of paraxial vacuum
propagation and turbulent phase accumulation. We present a
semi-analytic approach to evaluating the Fresnel diffraction integral
with one phase screen between the source and observation planes
and another screen in the observation plane. Specifically, we express
the first phase screen’s transmittance as a Fourier series,
which allows us to bring phase screen effects outside of the Fresnel
diffraction integral, thereby reducing the numerical computations.
This particular setup is useful for simulating astronomical imaging
geometries and two-screen laboratory experiments that emulate real
turbulence with phase wheels, spatial light modulators, etc. Further,
this is a key building block in more general semi-analytic split-step
simulations that have an arbitrary number of screens. Compared with
the standard angular-spectrum approach using the fast Fourier
transform, the semi-analytic method provides relaxed sampling
constraints and an arbitrary computational grid. Also, when a limited
number of observation-plane points is evaluated or when many time
steps or random draws are used, the semi-analytic method can compute
faster than the angular-spectrum method.