We demonstrate a novel method of two-dimensional differential interference contrast (DIC) microscopy. Our method is
cheaper, more compact, and more robust compared to conventional DIC microscopes; since it uses a simple variation of
Young's double-slit geometry, no expensive or complex optical components are needed. In addition, our method
quantitatively measures differential phase, unlike conventional DIC, which makes our device useful for optical
metrology and cell biology applications. The device consists of four circular holes arranged in a "plus" pattern, milled
into a metal layer 80 μm above a complimentary metal-oxide semiconductor (CMOS) image sensor. Light incident upon
the four-hole aperture is transmitted through the holes and creates an interference pattern on the CMOS sensor. This
pattern shifts as a function of the spatial phase gradient of the incident light. By capturing the amplitude and location of
the zero-order fringe of the interference pattern, the amplitude and differential phase of the incident light can be
measured simultaneously. In this article, we model the response of the device using both geometric optics and Huygens
principle. We then verify these models by experimentally measuring the responsivity of our device. A short analysis on
the algorithm used to calculate the fringe location follows. We then show a beam profiling application by measuring the
amplitude and spatial phase gradient of a Gaussian laser beam and an optical vortex. Finally, we show a DIC microscope
application; we image a phase mask of the letters "CIT".
This paper reports a complete on-chip high resolution lensless imaging device based on the optofluidic
microscopy method, which can form a vital optical microscopy component in a wide range of lab-on-a-chip
systems. This imaging device does not use any lens elements and yet is capable of resolution comparable to
that of a conventional microscope with a 20× objective. We demonstrate the use of the device for
Caenorhabditis elegans and microsphere imaging at a resolution of ~ 1 μm with an imaging time of ~2 sec.
The fabrication of this on-chip imaging device is fully compatible with existing semiconductor and
microfluidic technologies, so the device can be massively fabricated and integrated into microsystems to
form compact and low-cost total analysis systems for biological and colloidal studies.
Our group has reported the use of harmonically matched diffraction grating for full-field quantitative phase imaging. In
this paper, we show the improvement of this technique and the application in observing dynamics of transparent
samples. By using the grating as a beam splitter/combiner in an interferometer, we are able to obtain non-trivial phase
difference between the output ports of the grating. We have built a Mach-Zehnder interferometer using the holographic
grating with 600 and 1200 lines/mm spacing. Two CCD cameras at the output ports of the grating-based Mach-Zehnder
interferometer are used to record the full-field quadrature interferograms, which are subsequently processed to
reconstruct the phase image. Since the two quadrature interferograms are acquired at the same time, the imaging speed
of the system is limited only by the frame rate of the CCD cameras. We have demonstrated the capability of our system
by observing dynamics of transparent samples.
We report a new method for obtaining non-trivial phase difference between the output ports of an interferometer
through the use of shallow diffraction gratings. We show that as opposed to a single shallow diffraction grating-based
interferometer (which provides only trivial phase shifts, i.e., 0° or 180°), a pair of harmonically-related shallow
diffraction gratings can be used to design interferometers with non-trivial phase shifts between different output ports.
More importantly, the phase shifts can be adjusted by simply shearing one grating with respect to the other. This
approach does not change the path length relationships of the different interference beams within the interferometer,
which is an advantage for metrology and low coherence interferometry applications.
In this paper, we will report our recent development of a new type of
OptoFluidic Microscope (OFM) that is capable of delivering resolution beyond the
diffraction limit of light. Accurate control of the sample translation is accomplished
by adopting an optical tweezer scanner into the system. During the image acquisition,
a two-dimensional nanoaperture array defined on a thin aluminum film acts as an
array of ultra-fine illumination sources. The imaging system is tested and
demonstrated by using polystyrene beads and green algae (Chlamydomonas).
Properties of the system are reported and discussed.
In this article, we will present a novel differential interference contrast (DIC) phase imaging device based
on Young's interference. It is mainly based on either two or four nano apertures defined in an optically
opaque aluminum film on a CMOS imaging sensor chip. It provides linear and disentangled differential
phase and intensity images simultaneously. Furthermore, it's simple, free of bulky optical elements and
compatible to the planar micro fabrication process. All of these features make it a promising device for the
on-chip high resolution DIC phase imaging and beam profiling. The fabrication and operation of the device
is explained in details. The performance is evaluated theoretically and is verified experimentally by
examining the phase and intensity profile of a Gaussian beam and an optical vortex. The 2D quantitive
differential phase distribution of an optical vortex has been recorded directly by our device with 1μm
resolution.
In this paper, we report the use of holographic gratings, which act as the free-space equivalent of the 3x3 fiber-optic
coupler, to perform full field phase imaging. By recording two harmonically-related gratings in the same holographic
plate, we are able to obtain nontrivial phase shift between different output ports of the gratings-based Mach-Zehnder
interferometer. The phase difference can be adjusted by changing the relative phase of the recording beams when
recording the hologram. We have built a Mach-Zehnder interferometer using harmonically-related holographic gratings
with 600 and 1200 lines/mm spacing. Two CCD cameras at the output ports of the gratings-based Mach-Zehnder
interferometer are used to record the full-field quadrature interferograms, which are subsequently processed to
reconstruct the phase image. The imaging system has ~12X magnification with ~420μmx315μm field-of-view. To
demonstrate the capability of our system, we have successfully performed phase imaging of a pure phase object and a
paramecium caudatum.
We review the current state of research in endoscopic optical coherence tomography (OCT). We first survey the range of available endoscopic optical imaging techniques. We then discuss the various OCT-based endoscopic methods that have thus far been developed. We compare the different endoscopic OCT methods in terms of their scan performance. Next, we examine the application range of endoscopic OCT methods. In particular, we look at the reported utility of the methods in digestive, intravascular, respiratory, urinary and reproductive systems. We highlight two additional applications—biopsy procedures and neurosurgery—where sufficiently compact OCT-based endoscopes can have significant clinical impacts.
KEYWORDS: Microfluidics, Imaging systems, Microscopes, Charge-coupled devices, Signal to noise ratio, Near field scanning optical microscopy, Imaging devices, Animal model studies, Lab on a chip, Microscopy
We demonstrate a novel optical imaging device that can be directly integrated into a microfluidic network, and therefore enables on-chip imaging in a microfluidic system. This micro imaging device, termed optofluidic microscope (OFM) is free of bulk optics and is based on a nanohole array defined in a non-transmissive metallic layer that is patterned onto the floor of the microfluidic channel. The operation of the optofluidic microscope will be explained in details and its performance is examined by using a popular animal model, Caenorhabditis elegans (C. elegans). Images from a large population of nematode worms are efficiently acquired within a short time frame. The quality of the OFM images of C. elegans and the morphological characteristics revealed therein are evaluated. Two groups of early-stage C. elegans larvae, wild-type and dpy-24 are successfully separated even though their morphological difference at the larval stage is subtle. The experimental results support our claim that the methodology described therein can be effectively used to develop a powerful tool for fulfilling high-resolution, high-throughput imaging task in microfluidics-based systems.
The use of indocyanine green (ICG), a U.S. Food and Drug Administration approved dye, in a pump-probe scheme for molecular contrast optical coherence tomography (MCOCT) is proposed and demonstrated for the first time. In the proposed pump-probe scheme, an optical coherence tomography (OCT) scan of the sample containing ICG is first acquired. High fluence illumination (~190 kJ/cm2) is then used to permanently photobleach the ICG molecules—resulting in a permanent alteration of the overall absorption of the ICG. A second OCT scan is next acquired. The difference of the two OCT scans is used to determine the depth resolved distribution of ICG within a sample. To characterize the extent of photobleaching in different ICG solutions, we determine the cumulative probability of photobleaching, B,cum, defined as the ratio of the total photobleached ICG molecules to the total photons absorbed by the ground state molecules. An empirical study of ICG photobleaching dynamics shows that B,cum decreases with fluence as well as with increasing dye concentration. The quantity B,cum is useful for estimating the extent of photobleaching in an ICG sample (MCOCT contrast) for a given fluence of the pump illumination. The paper also demonstrates ICG-based MCOCT imaging in tissue phantoms as well as within stage 54 Xenopus laevis.
In this paper, we present a novel high resolution optical imaging device on chip. It is based on a line of nano holes defined in an optically opaque aluminum film on a CMOS imaging sensor chip. Because it's free of bulky optical elements and compatible to the planar micro fabrication process, it is very promising to become an important component for the on-chip high resolution imaging in the future. The fabrication and operation of this novel on-chip microscope is explained in details. The performance is evaluated
theoretically and is verified experimentally by examining the profile of a laser spot formed by a 10X objective lens.
KEYWORDS: Microfluidics, Microscopes, Imaging systems, Signal to noise ratio, Image resolution, Charge-coupled devices, Biology, Imaging devices, Animal model studies, Lab on a chip
In this article, we will demonstrate a novel optical imaging device that can be directly integrated into a microfluidic network, and therefore enables on-chip imaging in a microfluidic system. This micro imaging device, termed optofluidic microscope (OFM) is potentially free of bulk optics and is based on a nanohole array defined in a nontransmissive metallic layer that is patterned onto the floor of the microfluidic channel. The operation of the optofluidic microscope will be explained in details and its performance is examined by using a popular animal model, Caenorhabditis elegans (C. elegans). Images from a large population of nematode worms are efficiently acquired within a short time frame. The quality of the OFM images of C. elegans and the morphological characteristics revealed therein are evaluated. Two groups of early-stage C elegans larvae, wild-type and dpy-24 are successfully separated even though their morphological difference at the larval stage is subtle. The experimental results support our claim that the methodology described therein can be effectively used to develop a powerful tool for fulfilling high-resolution, highthroughput imaging task in microfluidics-based systems.
KEYWORDS: Microfluidics, Microscopes, Imaging systems, Charge-coupled devices, Signal to noise ratio, Microscopy, Imaging devices, Aluminum, Gold, Near field optics
In this work, we present a novel optical imaging device that can be directly integrated into a microfluidic network, and can therefore enable on-chip imaging in a microfluidic system. This micro imaging device, termed optofluidic microscope (OFM) is free of bulk optics and is based on a nanohole array defined in a non-transmissive metallic layer that is patterned onto the floor of the microfluidic channel. The operation of the optofluidic microscope is explained in details and its performance is examined with Caenorhabditis elegans (C. elegans) of various genotypes. Images from a large population of worms have been efficiently acquired within a short time frame. The quality of the OFM images of C elegans and the morphological characteristics revealed by the images are evaluated. The experimental results support our claim that the methodology described therein promises to create a powerful tool for fulfilling high- resolution, high-throughput imaging task of the microscopic biological samples.
"Optofluidics" is the marriage of optics, optoelectronics and nanophotonics with fluidics. Such integration represents a new approach for dynamic manipulation of optical properties at length scales both greater than and smaller than the wavelength of light with applications ranging from reconfigurable photonic circuits to fluidically adaptable optics to high sensitivity bio-detection currently under development. The capabilities in terms of fluidic control, mixing, miniaturization and optical property tuning afforded by micro-, nano- and electro-fluidics combined with soft lithography based fabrication provides an ideal platform upon which to build such devices. In this paper we provide a general overview of some of the important issues related to the fabrication, integration and operation of optofluidic devices and present three comprehensive application examples: nanofluidically tunable photonic crystals, optofluidic microscopy and DFB dye lasers.
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