Techniques for fast and sensitive measurements of two-dimensional birefringence distributions
TL;DR: In this article, the authors proposed image processing algorithms for measuring two-dimensional distributions of linear birefringence using a pair of variable retarders and obtained the lowest noise level of 0.036 nm.
Abstract: We propose image processing algorithms for measuring two-dimensional distributions of linear birefringence using a pair of variable retarders. Several algorithms that use between two and five recorded frames allow us to optimize measurements for speed, sensitivity, and accuracy. We show images of asters, which consist of radial arrays of microtubule polymers recorded with a polarized light microscope equipped with a universal compensator. Our experimental results confirm our theoretical expectations. The lowest noise level of 0.036 nm was obtained when we used the five-frame technique and four-frame algorithm without extinction setting. The two-frame technique allows us to increase the speed of measurement with acceptable image quality.
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Patent•
13 Dec 2007
TL;DR: In this paper, a method for increasing the sensitivity in the detection of optical coherence tomography and low coherence interferometry (LCI) signals by detecting a parallel set of spectral bands, each band being a unique combination of optical frequencies, is presented.
Abstract: Apparatus and method for increasing the sensitivity in the detection of optical coherence tomography and low coherence interferometry (“LCI”) signals by detecting a parallel set of spectral bands, each band being a unique combination of optical frequencies. The LCI broad bandwidth source is split into N spectral bands. The N spectral bands are individually detected and processed to provide an increase in the signal-to-noise ratio by a factor of N. Each spectral band is detected by a separate photo detector and amplified. For each spectral band the signal is band pass filtered around the signal band by analog electronics and digitized, or, alternatively, the signal may be digitized and band pass filtered in software. As a consequence, the shot noise contribution to the signal is reduced by a factor equal to the number of spectral bands. The signal remains the same. The reduction of the shot noise increases the dynamic range and sensitivity of the system.
446 citations
Patent•
08 Sep 2004
TL;DR: In this article, the first and/or second electro-magnetic radiations have a spectrum whose mean frequency changes substantially continuously over time at a tuning speed that is greater than 100 Tera Hertz per millisecond.
Abstract: An apparatus and method are provided. In particular, at least one first electro-magnetic radiation may be provided to a sample and at least one second electro-magnetic radiation can be provided to a non-reflective reference. A frequency of the first and/or second radiations varies over time. An interference is detected between at least one third radiation associated with the first radiation and at least one fourth radiation associated with the second radiation. Alternatively, the first electro-magnetic radiation and/or second electro-magnetic radiation have a spectrum which changes over time. The spectrum may contain multiple frequencies at a particular time. In addition, it is possible to detect the interference signal between the third radiation and the fourth radiation in a first polarization state. Further, it may be preferable to detect a further interference signal between the third and fourth radiations in a second polarization state which is different from the first polarization state. The first and/or second electro-magnetic radiations may have a spectrum whose mean frequency changes substantially continuously over time at a tuning speed that is greater than 100 Tera Hertz per millisecond.
394 citations
Patent•
29 Sep 2005
TL;DR: In this paper, a system and method for imaging of a sample, e.g., biological sample, are provided, where at least one source electro-magnetic radiation forwarded to the sample and a reference may be generated.
Abstract: A system and method for imaging of a sample, e.g., biological sample, are provided. In particular, at least one source electro-magnetic radiation forwarded to the sample and a reference may be generated. A plurality of detectors may be used, at least one of the detectors capable of detecting a signal associated with a combination of at least one first electro-magnetic radiation received from the sample and at least one second electro-magnetic radiation received from the reference. At least one particular detector may have a particular electrical integration time, and can receive at least a portion of the signal for a time duration which has a first portion with a first power level greater than a predetermined threshold and a second portion immediately preceding or following the first portion. The second portion may have a second power level that is less than the predetermined threshold, and extends for a time period which may be, e.g., approximately more than 10% of the particular electrical integration time.
393 citations
TL;DR: In this paper, a class of active matter called living liquid crystals (LLCs) is introduced, which combines living swimming bacteria with a lyotropic liquid crystal, and the physical properties of LLCs can be controlled by the amount of oxygen available to bacteria, by concentration of ingredients, or by temperature.
Abstract: Collective motion of self-propelled organisms or synthetic particles, often termed “active fluid,” has attracted enormous attention in the broad scientific community because of its fundamentally nonequilibrium nature. Energy input and interactions among the moving units and the medium lead to complex dynamics. Here, we introduce a class of active matter–living liquid crystals (LLCs)–that combines living swimming bacteria with a lyotropic liquid crystal. The physical properties of LLCs can be controlled by the amount of oxygen available to bacteria, by concentration of ingredients, or by temperature. Our studies reveal a wealth of intriguing dynamic phenomena, caused by the coupling between the activity-triggered flow and long-range orientational order of the medium. Among these are (i) nonlinear trajectories of bacterial motion guided by nonuniform director, (ii) local melting of the liquid crystal caused by the bacteria-produced shear flows, (iii) activity-triggered transition from a nonflowing uniform state into a flowing one-dimensional periodic pattern and its evolution into a turbulent array of topological defects, and (iv) birefringence-enabled visualization of microflow generated by the nanometers-thick bacterial flagella. Unlike their isotropic counterpart, the LLCs show collective dynamic effects at very low volume fraction of bacteria, on the order of 0.2%. Our work suggests an unorthodox design concept to control and manipulate the dynamic behavior of soft active matter and opens the door for potential biosensing and biomedical applications.
325 citations
TL;DR: In this paper, the angular compounding by path length encoding (ACPE) algorithm is proposed to reduce speckle in OCT images by averaging images obtained at different incident angles, with each image encoded by the path length.
Abstract: Speckle, a factor reducing image quality in optical coherence tomography ('OCT'), can limit the ability to identify cellular structures that are important for the diagnosis of a variety of diseases. The present invention allows for an implementation of an angular compounding, angular compounding by path length encoding ('ACPE') for reducing speckle in OCT images. By averaging images obtained at different incident angles, with each image encoded by path length, ACPE maintains high-speed image acquisition and implements minimal modifications to OCT probe optics. ACPE images obtained from tissue phantoms and human skin in vivo demonstrate a qualitative improvement over traditional OCT and an increased signal-to-noise ratio ('SNR'). Accordingly, apparatus probe catheter, and method are provided for irradiating a sample. In particular, an interferometer (5) may forward forwarding an electromagnetic radiation (10). In addition, a sample arm may receive the electromagnetic radiation, and can include an arrangement (20) which facilitates a production of at least two radiations (30, 40) from the electromagnetic radiation so as to irradiate the sample. Such arrangement can be configured to delay a first radiation of the at least two radiations with respect to a second radiation of the at least two radiations.
258 citations
References
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TL;DR: A new type of polarized light microscope for fast and orientation‐independent measurement of birefringent fine structure has been developed and incorporates a precision universal compensator made from two liquid crystal variable retarders.
Abstract: A new type of polarized light microscope ('new pol-scope') for fast and orientation-independent measurement of birefringent fine structure has been developed. The design of the new pol-scope incorporates a precision universal compensator made from two liquid crystal variable retarders. A video camera and digital image processing system provide fast measurements of specimen anisotropy (retardance magnitude and azimuth) at all points of the image forming the field of view. The images document fine structural and molecular organization within a thin optical section of the specimen. The sensitivity of the current instrument is 0.1 nm of specimen retardance, measured with data gathered in 0.43 s at all 640 x 480 image points. Examples of birefringence measurements in biological (microtubule arrays) and industrial (magneto-optical disc substrate) specimens are presented.
320 citations
IBM1
TL;DR: The present status of ellipsometric measurement capability is reviewed in this article, where significant advances since the last ellipsometry conference are highlighted, as well as the present state of the ellipsometrical measurement capability.
234 citations
TL;DR: The Mueller matrix imaging polarimeter (MMI polarimeter) as mentioned in this paper was designed to measure the polarization properties of a set of ray paths through a sample, which can be configured to make a wide variety of polarimetric measurements of optical systems and samples.
Abstract: The design and operation of a Mueller matrix imaging polarimeter is presented. The instrument is configurable to make a wide variety of polarimetric measurements of optical systems and samples. In one configuration, it measures the polarization properties of a set of ray paths through a sample. The sample may comprise a single element, such as a lens, polarizer, retarder, spatial light modulator, or beamsplitter, or an entire optical system containing many elements. In a second configuration, it measures an optical system's point spread matrix, a Mueller matrix relating the polarization state of a point object to the distribution of intensity and polarization across the image. The instrument is described and a number of example measurements are provided that demonstrate the Mueller matrix imaging polarimeter's unique measurement capability.
188 citations
TL;DR: In this paper, a new optical microscope imaging system is described, which is capable of producing coded colour images of an optically birefringent material, where the colour represents either $|$sin $\delta|$, a function of the optical retardation; or I${text{o}}$, the transmittance, at any place within the image.
Abstract: A new optical microscope imaging system is described. The instrument is capable of producing coded colour images of an optically birefringent material, where the colour represents either $|$sin $\delta|$, a function of the optical retardation; $\phi $, the orientation of a section of the optical indicatrix; or I$_{\text{o}}$, the transmittance, at any place within the image. Thus the contrast normally seen in a standard crossed-polars experiment is separated out into its components. The technique is both qualitative and quantitative. Examples of the application of this system to crystals, a rock section and a biological specimen are given.
185 citations
TL;DR: The birefringence of microtubules (MTs) and of MT-based macromolecular assemblies in vitro and in living cells is measured by using the new Pol-Scope and the theoretical concept is based on Wiener's theory of mixed dielectrics, which is well established for nonimaging applications.
149 citations