Phase imaging of cells by simultaneous dual-wavelength reflection digital holography

Abstract

We present a phase-imaging technique to quantitatively study the three-dimensional structure of cells. The method, based on the simultaneous dual-wavelength digital holography, allows for higher axial range at which the unambiguous phase imaging can be performed. The technique is capable of nanometer axial resolution. The noise level, which increases as a result of using two wavelengths, is then reduced to the level of a single wavelength. The method compares favorably to software unwrapping, as the technique does not produce non-existent phase steps. Curvature mismatch between the reference and object beams is numerically compensated. The 3D images of SKOV-3 ovarian cancer cells are presented.

Optically monitoring and controlling nanoscale topography during semiconductor etching

“…In particular, we present dynamic imaging data of semiconductor structures while being etched; epi-DPM reveals quantitatively the etch rate at each point in the image and each moment in time. We found this rate to vary significantly versus position and time with typical values in the range of 0-8 nm s 21 . Finally, we show that photochemical etching can be used in combination with epi-DPM imaging to controllably vary the etch rate across the sample and thereby fabricate 'gray-scale' structures, e.g., microlenses.…”

“…To exploit this feature, we imaged the topography of an n1 GaAs wafer while being etched with a solution of H 3 PO 4 :H 2 O 2 :H 2 O (see Supplementary Information for details on the processing steps). 23 We acquired 400 frames at 8.93 frames s 21 , for a total of 44.8 s. Our epi-DPM movie (Supplementary Movie) revealed that it took approximately 10 s for the etchant to diffuse into the field of view and begin etching. The montage in Figure 3a indicates the spatial inhomogeneity and the time evolution of the etching process.…”

“…Note that at the image plane, we obtain a magnified replica of the field reflected by the sample. The diffraction grating had 300 grooves mm 21 , blazed at an angle to maximize the power in the first diffraction order. Lens L 3 is used to generate the Fourier transform of the image field at its back focal plane.…”

“…This method essentially averages out the effects of speckles. 21,22 It also dithers the image, which reduces the quantization error. The Monitoring nanoscale topography during etching C Edwards et al 2 resulting epi-DPM images revealed that the spatial noise floor dropped to 10.4 nm after adding the diffuser.…”

White-light diffraction tomography of unlabelled live cells

“…In recent years, as a result of new advances in light sources, detector arrays and computing power, quantitative phase imaging (QPI), in which optical path-length delays are measured at each point in the field of view, has become a very active field of study 9 . Whether involving holographic or non-holographic methods 10-16 , QPI presents new opportunities for studying cells and tissues non-invasively, quantitatively and without the need for staining or tagging [17][18][19][20][21][22][23] . Projection tomography using laser QPI has made use of ideas from X-ray imaging and enabled three-dimensional imaging of transparent structures [24][25][26] .…”