Improved imaging of phase gradients in scanning optical microscopy

Abstract

SUMMARY Previous work has used a circular large area split detector for phase gradient imaging; it is shown that substituting an annular split detector offers improvements in frequency response, particularly for weak phase gradients. Transfer functions are calculated and transmission and reflection micrographs demonstrate the different imaging properties. Other forms of detector are also considered, some of these possessing certain advantages.

Quantitative differential phase contrast imaging in an LED array microscope

“…We linearize the problem by adopting a weak object approximation, o(r) ≈ 1 − µ(r) + iφ (r) [13,21,22], and neglecting the cross terms from µ and φ , so that…”

“…The phase derivative model [6,7] is only accurate in 1D and within the numerical aperture (NA) of the microscope objective [13,22]. We derive here the full 2D model for all spatial frequencies out to the partially coherent bandlimit of the objective.…”

“…The difference between the two images is related to the sample's phase derivative along the axis of asymmetry. Conveniently, DPC only requires hardware changes on the illumination side [7,11,12] or on the detection side [6,13,14], thus it can be integrated into existing systems (e.g. endoscopy [11]).…”

“…This phase transfer function analysis and reconstruction technique may also find use in its application to alternative DPC architectures based on split-detectors [6,13,14,23]. …”

“…In this paper, we derive the weak object transfer function (WOTF) [13,21] to quantify how phase information is converted into intensity in our DPC measurements, then develop quantitative inversion methods. The phase derivative model [6,7] is only accurate in 1D and within the numerical aperture (NA) of the microscope objective [13,22].…”