Comparison of Digital Holography and Transport of Intensity for Quantitative Phase Contrast Imaging

Extracting quantitative phase information has received increased interest in many fields where either phase imaging or structure retrieval is an issue, such as optical testing, bio-medical imaging and materials science. In the past couple of decades, digital holography (DH) has emerged as a front-runner for phase imaging by providing quantitative phase measurements of the wave field with high accuracy and in near real-time [1]. However, DH systems need a highly coherent light source, suffer phase aberration, ambiguity and unwrapping problems, and cannot offer the highest spatial resolution. Recently, however, direct phase retrieval from intensity measurements using the Transport-of-Intensity Equation (TIE) [2, 3] has gained increasing attention. A minimum of two measurements of the spatial intensity of the optical wave in closely spaced planes perpendicular to the direction of propagation are needed to reconstruct the spatial phase of the wave by solving a second-order differential equation, i.e., with a non-iterative deterministic algorithm. In this paper, these two quantitative phase imaging methods: DH and TIE are introduced and compared. Two samples: a regular array of micro-bumps fabricated on Si substrate based on laser induced non-ablative texturing and a refractive quartz microlens array from SUSS MicroOptics were tested by DH and TIE. The results were compared and the merits and limitations of each method are discussed.