Optical path difference microscopy with a Shack–Hartmann wavefront sensor

Abstract

In this Letter, we show that a Shack-Hartmann wavefront sensor can be used for the quantitative measurement of the specimen optical path difference (OPD) in an ordinary incoherent optical microscope, if the spatial coherence of the illumination light in the plane of the specimen is larger than the microscope resolution. To satisfy this condition, the illumination numerical aperture should be smaller than the numerical aperture of the imaging lens. This principle has been successfully applied to build a high-resolution reference-free instrument for the characterization of the OPD of micro-optical components and microscopic biological samples.

Single-shot phase contrast microscopy using polarisation-resolved differential phase contrast

“…An application of wide potential interest could be to provide label-free segmentation on existing fluorescence microscopes. There are many approaches to realize quantitative phase microscopy (QPM) including explicit interferometric techniques such as phase stepping interferometry, off-axis (digital) holography, shearing interferometry, techniques that reconstruct the phase of the electric field scattered by the sample from intensity measurements, such as transport of intensity 2,3 and (Fourier) ptychography 4 , and non-interferometric wavefront sensing approaches including the use of Shack Hartman sensors 5 or other phase gradient measurement techniques 6 , including differential phase contrast microscopy 7,8 . Most of the phase contrast techniques reported to date require specialist optical components (e.g.…”

Single-shot and lensless complex-amplitude imaging with incoherent light based on machine learning

“…Another approach for phase imaging with incoherent light is to use a Shack-Hartmann wavefront sensor [11]. Singleshot complex-amplitude/phase imaging methods based on the Shack-Hartmann wavefront sensor have utilized a lens array or a holographic optical element to observe a stereo or plenoptic image, and this results in a tradeoff between the spatial and angular resolutions [12][13][14][15][16][17]. Thus, these methods involve a compromise between the space-bandwidth product and the simplicity of the optical setup.…”

Wrapping-free numerical refocusing of scalar electromagnetic fields

“…[5][6][7][8][9][10][11][12]) -the most common technique being digital holography -and (ii) those which do not directly retreive the optical phase but rather a related quantity such as its transverse gradient map (see e.g. [13][14][15][16][17][18][19]) -the most common technique being wavefront sensing. In direct methods, phase is provided modulo 2π: phase is then said to be "wrapped".…”

“…The methods of the second phase-retrieval family are less prone to such artifacts because the measured quantity is not 2π-periodic. Wavefront sensor based methods [14][15][16][17] typically measure the wavefront derivatives rather than the phase map, so avoiding the wrapping problems.…”