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Digital holographic reconstruction without window (a-c) and with window “d” (d-f). From left to right: amplitude, wrapped and unwrapped phase.
Source publication
We introduce depth-filtered digital holography (DFDH) as a method for quantitative tomographic phase imaging of buried layers in multilayer samples. The procedure is based on the acquisition of multiple holograms for different wavelengths. Analyzing the intensity over wavelength pixel wise and using an inverse Fourier transform leads to a depth-pro...
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Here we describe a new holographic recording method in which a separate reference wave is not required. Object wave is split into two beams and one of them is spatially filtered to create a plane reference wave. This method allows the use of low coherence light sources since pathlengths of the interfering waves are matched automatically which will...
Citations
... The precise quantitative phase imaging performance can be hardly achieved using other endoscopes illuminated by incoherent light sources due to the wide spectrum of the light source. Digital holography is a common method for quantitative phase imaging 49,50 , however, digital holographic imaging with long MCFs requires complex optical systems and tedious optical alignment 44,51 . Our proposed FAST reconstruction method does not require digital holography, the precise amplitude and phase images of the sample can be recovered from an intensity-only speckle. ...
Quantitative phase imaging (QPI) is a label-free technique providing both morphology and quantitative biophysical information in biomedicine. However, applying such a powerful technique to in vivo pathological diagnosis remains challenging. Multi-core fiber bundles (MCFs) enable ultra-thin probes for in vivo imaging, but current MCF imaging techniques are limited to amplitude imaging modalities. We demonstrate a computational lensless microendoscope that uses an ultra-thin bare MCF to perform quantitative phase imaging with microscale lateral resolution and nanoscale axial sensitivity of the optical path length. The incident complex light field at the measurement side is precisely reconstructed from the far-field speckle pattern at the detection side, enabling digital refocusing in a multi-layer sample without any mechanical movement. The accuracy of the quantitative phase reconstruction is validated by imaging the phase target and hydrogel beads through the MCF. With the proposed imaging modality, three-dimensional imaging of human cancer cells is achieved through the ultra-thin fiber endoscope, promising widespread clinical applications.
... The precise quantitative phase imaging performance can be hardly achieved using other endoscopes illuminated by incoherent light sources due to the wide spectrum of the light source. Digital holography is a common method for quantitative phase imaging (48,49), however, digital holographic imaging with long MCFs requires complex optical systems and tedious optical alignment (43,50). Our proposed FAST reconstruction method does not require digital holography, the precise amplitude and phase images of the sample can be recovered from an intensity-only speckle. ...
Quantitative phase imaging (QPI) is a label-free technique providing both morphology and quantitative biophysical information in biomedicine. However, applying such a powerful technique to in vivo pathological diagnosis remains challenging. Multi-core fiber bundles (MCFs) enable ultra-thin probes for in vivo imaging, but current MCF imaging techniques are limited to amplitude imaging modalities. We demonstrate a computational lensless microendoscope that uses an ultra-thin bare MCF to perform quantitative phase imaging of biomedical samples with up to 1 {\mu}m lateral resolution and nanoscale axial resolution. The incident complex light field at the measurement side is precisely reconstructed from a single-shot far-field speckle pattern at the detection side, enabling digital focusing and 3D volumetric reconstruction without any mechanical movement. The accuracy of the quantitative phase reconstruction is validated by imaging the phase target and hydrogel beads through the MCF. With the proposed imaging modality, 3D imaging of human cancer cells is achieved through the ultra-thin fiber endoscope, promising widespread clinical applications.
... Combining high sensitivity and flexibility, this method is attractive to be used for research. Moreover, the digital acquisition of data allows for data processing and numerical propagation of the wavefield to any plane of interest [4]. The direct phase retrieval and its differential nature, make digital holographic interferometry an attractive tool for the study of heat transfer phenomena [5]. ...
In this paper, we present a method of quantitatively measuring in real-time the dynamic temperature field change and visualization of volumetric temperature fields generated by a 2D axial-symmetric heated fluid from a pulsatile jet in a water tank through off-axis digital holographic interferometry. A Mach-Zehnder interferometer on portable platform was built for the experimental investigation. The pulsatile jet was submerged in a water tank and fed with water with higher temperature. Tomographic approach was used to reconstruct the temperature fields through the Abel Transform and the filtered back-projection. Averaged results, tomographic view, standard deviation and errors are presented. The presented results reveal digital holographic interferometry as a powerful technique to visualize temperature fields in flowing liquids and gases.
... For DHM systems, the investigation of buried structures is still very challenging and represents an emerging field of research. A number of different depth-filtering approaches have been presented recently in order to address this challenge [26][27][28][29][30]. However, they require complex pinhole alignment, multiple wavelength scanning, additional numerical reconstruction algorithms, and highly sophisticated equipment or are applied only in transmission geometry. ...
In this paper, we present a confocal laser scanning holographic microscope for the investigation of buried structures. The multimodal system combines high diffraction limited resolution and high signal-to-noise-ratio with the ability of phase acquisition. The amplitude and phase imaging capabilities of the system are shown on a test target. For the investigation of buried integrated semiconductor structures, we expand our system with an optical beam induced current modality that provides additional structure-sensitive contrast. We demonstrate the performance of the multimodal system by imaging the buried structures of a microcontroller through the silicon backside of its housing in reflection geometry.
... However it was shown that by a sophisticated combination of a spectroscopy and a QPI technique, structures could be analyzed through silicon substrates [13]. In addition, low coherence sources and multiple wavelengths are used to reduce these depth filtering problems [14,15]. Furthermore advanced techniques adopting speckle illumination help to reduce noise and increase the optical sectioning capability [16,17]. ...
We demonstrate a method to select different layers in a sample using a low coherent gating approach combined with a stable common-path quantitative phase imaging microscopy setup. The depth-filtering technique allows us to suppress the negative effects generated by multiple interference patterns of overlaying optical interfaces in the sample. It maintains the compact and stable common-path setup, while enabling images with a high phase sensitivity and acquisition speed. We use a holographic microscope in reflective geometry with a non-tunable low coherence light source. First results of this technique are shown by imaging the hardware layer of a standard micro-controller through its thinned substrate.
... For multilayered phase boundaries more sophisticated setups based on tomographic phase acquisition are required, as otherwise reflections at upper layers may disturb the phase measurement. This can be, for example, achieved using illumination with short coherence length or with a swept laser as described in [43][44][45][46]. The Fresnel reflex at the desired phase boundary can be selected by appropriately locating the coherence gate. ...
Imaging-based flow measurement techniques, like particle image velocimetry (PIV), are vulnerable to time-varying distortions like refractive index inhomogeneities or fluctuating phase boundaries. Such distortions strongly increase the velocity error, as the position assignment of the tracer particles and the decrease of image contrast exhibit significant uncertainties. We demonstrate that wavefront shaping based on spatially distributed guide stars has the potential to significantly reduce the measurement uncertainty. Proof of concept experiments show an improvement by more than one order of magnitude. Possible applications for the wavefront shaping PIV range from measurements in jets and film flows to biomedical applications.
... In this Letter, we demonstrate phase imaging of a sample that can be resolved neither with common intensity-based processing nor by regular phase resolved processing using a standard SD-OCT system. Instead, we combined multiple phase maps obtained by depth filtered digital holography (DFDH) [3] with a multiwavelength phase unwrapping algorithm [4]. We corrected the measurement for aberrations in a semi-automated procedure [5]. ...
... Previously we used DFDH in a full-field OCT setup in off-axis geometry and filtered out spurious reflections of a multilayer sample to obtain a height profile using one phase map [3]. In the original work, aberrations of the measurements were not taken into account. ...
... Due to the depth filtering, the proposed technique can also be used for measurements in multilayer semitransparent samples [3,11]. As a next step, we want to develop an automated algorithm that takes the noise of the measurement and the information provided by intensity into account. ...
In this Letter, we present a new approach to processing data from a standard spectral domain optical coherence tomography (OCT) system using depth filtered digital holography (DFDH). Intensity-based OCT processing has an axial resolution of the order of a few micrometers. When the phase information is used to obtain optical path length differences, subwavelength accuracy can be achieved, but this limits the resolvable step heights to half of the wavelength of the system. Thus there is a metrology gap between phase- and intensity-based methods. Our concept addresses this metrology gap by combining DFHD with multiwavelength phase unwrapping. Additionally, the measurements are corrected for aberrations. Here, we present proof of concept measurements of a structured semiconductor sample.
We demonstrate the potential of spatial light modulators for the spectral control of a broadband source in digital holographic microscopy. Used in a ‘pulse-shaping’ geometry, the spatial light modulator provides a versatile control over the bandwidth and wavelength of the light source. The control of these properties enables adaptation to various experimental conditions. As a first application, we show that the source bandwidth can be adapted to the off-axis geometry to provide quantitative phase imaging over the whole field of view. As a second application, we generate sequences of appropriate wavelengths for a hierarchical optical phase unwrapping algorithm, which enables the measurement of the topography of high-aspect ratio structures without phase ambiguity. Examples are given with step heights up to 50 µm.
