  A new reference design is introduced for holographic coherent diffraction
imaging. This consists in two references - "block" and "pinhole" shaped regions
- placed adjacent to the imaging specimen. An efficient recovery algorithm is
provided for the resulting holographic phase retrieval problem, which is based
on solving a structured, overdetermined linear system. Analysis of the expected
recovery error on noisy data, which is contaminated by Poisson shot noise,
shows that this simple modification synergizes the individual references and
hence leads to uniformly superior performance over single-reference schemes.
Numerical experiments on simulated data confirm the theoretical prediction, and
the proposed dual-reference scheme achieves a smaller recovery error than
leading single-reference schemes.
