Abstract
Quantitative phase imaging systems using white light illumination can exhibit lower noise figures than laser-based systems. However, they can also suffer from object-dependent artifacts, such as halos, which prevent accurate reconstruction of the surface topography. In this work, we show that white light diffraction phase microscopy using a standard halogen lamp can produce accurate height maps of even the most challenging structures provided that there is proper spatial filtering at: 1) the condenser to ensure adequate spatial coherence and 2) the output Fourier plane to produce a uniform reference beam. We explain that these object-dependent artifacts are a high-pass filtering phenomenon, establish design guidelines to reduce the artifacts, and then apply these guidelines to eliminate the halo effect. Since a spatially incoherent source requires significant spatial filtering, the irradiance is lower and proportionally longer exposure times are needed. To circumvent this tradeoff, we demonstrate that a supercontinuum laser, due to its high radiance, can provide accurate measurements with reduced exposure times, allowing for fast dynamic measurements.
Highlights
Diffraction phase microscopy (DPM) is a Quantitative phase imaging (QPI) method that was first demonstrated in 2006 using laser illumination [2]
In the Appendix, we present measurement data showing that the temporal coherence of the white light DPM (wDPM) light source is at least an order of magnitude larger than what is needed to measure the samples discussed in this paper
The measured heights are correct and the images are free of halo and shade-off artifacts. This is due to the fact that, while the supercontinuum laser (SCL) is temporally broadband, it has adequate spatial coherence without any additional filtering by the condenser aperture
Summary
QPI methods exploit the fact that the phase of the imaging field is typically much more informative than its amplitude [1]. DPM utilizes a compact Mach-Zehnder interferometer to combine many of the best attributes of current QPI methods [2,3,4] This common-path geometry inherently cancels out most mechanisms responsible for noise and the single-shot measurement allows acquisition rates limited only by the speed of the camera employed. White light imaging systems using standard halogen lamp illumination can exhibit lower spatial phase noise than their laser counterparts [3, 4, 14, 18] This is a result of the lower coherence, both spatially and temporally, which reduces some noise mechanisms such as speckle [19]. The spatial filtering used to obtain adequate spatial coherence reduces the illuminating power This in turn increases the necessary camera exposure time and prevents highthroughput real-time imaging [17]. We solve this tradeoff by showing that the much higher radiance of a supercontinuum laser results in accurate measurements with low exposure times
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