We compare wave-front measurements using double-exposure digital holography and a Shack-Hartmann sensor. A voltage-driven liquid-crystal wedge modulates the optical wave front and provides a refractive-index gradient typical of interesting transparent materials. Measurement accuracy and reliability are similar for both methods. In our opinion, digital holographic interferometry has several advantages for both laboratory and field environments. When compared with Shack-Hartmann methods, these advantages include hardware simplicity and robustness, relative insensitivity to sample dynamic range, and less computational demanding and more straightforward data evaluation algorithms. We believe that digital holography provides the methodology of choice for field studies of transparent materials such as microgravity protein crystal growth experiments.
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