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Lynford L. Goddard

Bio: Lynford L. Goddard is an academic researcher from University of Illinois at Urbana–Champaign. The author has contributed to research in topics: Semiconductor laser theory & Laser. The author has an hindex of 30, co-authored 202 publications receiving 3174 citations. Previous affiliations of Lynford L. Goddard include Stanford University & Lawrence Livermore National Laboratory.


Papers
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Journal ArticleDOI
TL;DR: In this article, the authors present a diffraction phase microscopy (DPM) system, which is a common-path quantitative phase imaging (QPI) method that significantly alleviates the noise problem.
Abstract: The main obstacle in retrieving quantitative phase with high sensitivity is posed by the phase noise due to mechanical vibrations and air fluctuations that typically affect any interferometric system. In this paper, we review diffraction phase microscopy (DPM), which is a common-path quantitative phase imaging (QPI) method that significantly alleviates the noise problem. DPM utilizes a compact Mach–Zehnder interferometer to combine several attributes of current QPI methods. This compact configuration inherently cancels out most mechanisms responsible for noise and is single-shot, meaning that the acquisition speed is limited only by the speed of the camera employed. This technique is also nondestructive and does not require staining or coating of the specimen. This unique collection of features enables the DPM system to accurately monitor the dynamics of various nanoscale phenomena in a wide variety of environments. The DPM system can operate in both transmission and reflection modes in order to accommodate both transparent and opaque samples, respectively. Thus, current applications of DPM include measuring the dynamics of biological samples, semiconductor wet etching and photochemical etching processes, surface wetting and evaporation of water droplets, self-assembly of nanotubes, expansion and deformation of materials, and semiconductor wafer defect detection. Finally, DPM with white light averages out much of the speckle background and also offers potential for spectroscopic measurements.

322 citations

PatentDOI
TL;DR: In this article, the authors used a temporally incoherent source and light collected in transmission or scattering is used to generate a scattered phase image of the specimen in multiple axial planes, and a derived instrument function is deconvolved to obtain specimen susceptibility in wavevector space.
Abstract: Methods for obtaining a tomographic phase image of a specimen, either in transmission or in scatter. A specimen is illuminated by a temporally incoherent source and light collected in transmission or scattering is used to generate a scattered phase image of the specimen in multiple axial planes. The scattered field is solved for in wavevector space, and a derived instrument function is deconvolved to obtain specimen susceptibility in wavevector space. The specimen susceptibility is transformed to obtain a three-dimensional phase tomogram of the specimen.

301 citations

Journal ArticleDOI
TL;DR: A method for determining the core and cladding refractive indices of a microring resonator from its measured quasi-transverse electric and magnetic resonant modes and uses the singular value decomposition method to find the best fit parameters for the measured data.
Abstract: We present a method for determining the core and cladding refractive indices of a microring resonator from its measured quasi-transverse electric and magnetic resonant modes. We use single wavelength reflective microrings to resolve the azimuthal order ambiguity of the measured resonances. We perform accurate electromagnetic simulations to model the dependence of the resonances on geometrical and material parameters. We linearize the model and use the singular value decomposition method to find the best fit parameters for the measured data. At 1550 nm, we determine n(Si(3)N(4))=1.977±0.003 for stoichiometric silicon nitride deposited using low-pressure chemical vapor deposition (LPCVD) technique and n(SiO(x))=1.428±0.011 for plasma-enhanced chemical vapor deposition (PECVD) oxide. By measuring the temperature sensitivities of microring resonant modes with different polarizations, we find the thermo-optic coefficient of the stoichiometric silicon nitride to be dn(Si(3)N(4))/dT=(2.45±0.09)×10(-5) (RIU/°C) and the PECVD oxide to be dn(SiO(x))/dT=(0.95±0.10)×10(-5) (RIU/°C).

218 citations

Journal ArticleDOI
24 Jun 2014-ACS Nano
TL;DR: In vitro and in vivo investigations of Si NMs and other transient electronic materials demonstrate biocompatibility and bioresorption, thereby suggesting potential for envisioned applications in active, biodegradable electronic implants.
Abstract: Single-crystalline silicon nanomembranes (Si NMs) represent a critically important class of material for high-performance forms of electronics that are capable of complete, controlled dissolution when immersed in water and/or biofluids, sometimes referred to as a type of "transient" electronics. The results reported here include the kinetics of hydrolysis of Si NMs in biofluids and various aqueous solutions through a range of relevant pH values, ionic concentrations and temperatures, and dependence on dopant types and concentrations. In vitro and in vivo investigations of Si NMs and other transient electronic materials demonstrate biocompatibility and bioresorption, thereby suggesting potential for envisioned applications in active, biodegradable electronic implants.

164 citations

Journal ArticleDOI
TL;DR: In this article, a non-destructive optical imaging technique that combines a conventional microscope with a compact Mach-Zehnder interferometer is used to measure etch rates at each location across the sample with resolution of 0.085 nm s−1 per pixel.
Abstract: Semiconductor etching can now be monitored in real time at nanoscale resolution using a non-destructive optical imaging technique that combines a conventional microscope with a compact Mach–Zehnder interferometer. Developed by Chris Edwards, Amir Arbabi, Gabriel Popescu, and Lynford Goddard at the University of Illinois at Urbana-Champaign in the United States, epi-diffraction phase microscopy makes it possible to collect three-dimensional videos of semiconductor fabrication processes using a CCD camera. The approach is able to measure etch rates at each location across the sample with a resolution of 0.085 nm s−1 per pixel. Such an in situ monitoring capability could be useful for improving the manufacturing quality of a wide variety of semiconductor devices.

122 citations


Cited by
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Journal Article
TL;DR: In this article, a fast Fourier transform method of topography and interferometry is proposed to discriminate between elevation and depression of the object or wave-front form, which has not been possible by the fringe-contour generation techniques.
Abstract: A fast-Fourier-transform method of topography and interferometry is proposed. By computer processing of a noncontour type of fringe pattern, automatic discrimination is achieved between elevation and depression of the object or wave-front form, which has not been possible by the fringe-contour-generation techniques. The method has advantages over moire topography and conventional fringe-contour interferometry in both accuracy and sensitivity. Unlike fringe-scanning techniques, the method is easy to apply because it uses no moving components.

3,742 citations

Journal ArticleDOI
21 Nov 2014-Science
TL;DR: Results that take their cue from theoretical ideas of parity-time symmetry and implement them into the design of coupled laser components show that loss and gain can actually work together.
Abstract: Effective manipulation of cavity resonant modes is crucial for emission control in laser physics and applications. Using the concept of parity-time symmetry to exploit the interplay between gain and loss (i.e., light amplification and absorption), we demonstrate a parity-time symmetry-breaking laser with resonant modes that can be controlled at will. In contrast to conventional ring cavity lasers with multiple competing modes, our parity-time microring laser exhibits intrinsic single-mode lasing regardless of the gain spectral bandwidth. Thresholdless parity-time symmetry breaking due to the rotationally symmetric structure leads to stable single-mode operation with the selective whispering-gallery mode order. Exploration of parity-time symmetry in laser physics may open a door to next-generation optoelectronic devices for optical communications and computing.

1,336 citations

Journal ArticleDOI
16 Jul 2012-Sensors
TL;DR: This paper focuses on sensitivity and selectivity for performance indicators to compare different sensing technologies, analyzes the factors that influence these two indicators, and lists several corresponding improved approaches.
Abstract: Sensing technology has been widely investigated and utilized for gas detection. Due to the different applicability and inherent limitations of different gas sensing technologies, researchers have been working on different scenarios with enhanced gas sensor calibration. This paper reviews the descriptions, evaluation, comparison and recent developments in existing gas sensing technologies. A classification of sensing technologies is given, based on the variation of electrical and other properties. Detailed introduction to sensing methods based on electrical variation is discussed through further classification according to sensing materials, including metal oxide semiconductors, polymers, carbon nanotubes, and moisture absorbing materials. Methods based on other kinds of variations such as optical, calorimetric, acoustic and gas-chromatographic, are presented in a general way. Several suggestions related to future development are also discussed. Furthermore, this paper focuses on sensitivity and selectivity for performance indicators to compare different sensing technologies, analyzes the factors that influence these two indicators, and lists several corresponding improved approaches.

1,018 citations

Journal ArticleDOI
TL;DR: This Review presents the main principles of operation and representative basic and clinical science applications of quantitative phase imaging, and aims to provide a critical and objective overview of this dynamic research field.
Abstract: Quantitative phase imaging (QPI) has emerged as a valuable method for investigating cells and tissues. QPI operates on unlabelled specimens and, as such, is complementary to established fluorescence microscopy, exhibiting lower phototoxicity and no photobleaching. As the images represent quantitative maps of optical path length delays introduced by the specimen, QPI provides an objective measure of morphology and dynamics, free of variability due to contrast agents. Owing to the tremendous progress witnessed especially in the past 10–15 years, a number of technologies have become sufficiently reliable and translated to biomedical laboratories. Commercialization efforts are under way and, as a result, the QPI field is now transitioning from a technology-development-driven to an application-focused field. In this Review, we aim to provide a critical and objective overview of this dynamic research field by presenting the scientific context, main principles of operation and current biomedical applications. Over the past 10–15 years, quantitative phase imaging has moved from a research-driven to an application-focused field. This Review presents the main principles of operation and representative basic and clinical science applications.

847 citations

Journal ArticleDOI
04 Feb 2016-Nature
TL;DR: Material, device architectures, integration strategies, and in vivo demonstrations in rats of implantable, multifunctional silicon sensors for the brain, for which all of the constituent materials naturally resorb via hydrolysis and/or metabolic action, eliminating the need for extraction.
Abstract: Many procedures in modern clinical medicine rely on the use of electronic implants in treating conditions that range from acute coronary events to traumatic injury. However, standard permanent electronic hardware acts as a nidus for infection: bacteria form biofilms along percutaneous wires, or seed haematogenously, with the potential to migrate within the body and to provoke immune-mediated pathological tissue reactions. The associated surgical retrieval procedures, meanwhile, subject patients to the distress associated with re-operation and expose them to additional complications. Here, we report materials, device architectures, integration strategies, and in vivo demonstrations in rats of implantable, multifunctional silicon sensors for the brain, for which all of the constituent materials naturally resorb via hydrolysis and/or metabolic action, eliminating the need for extraction. Continuous monitoring of intracranial pressure and temperature illustrates functionality essential to the treatment of traumatic brain injury; the measurement performance of our resorbable devices compares favourably with that of non-resorbable clinical standards. In our experiments, insulated percutaneous wires connect to an externally mounted, miniaturized wireless potentiostat for data transmission. In a separate set-up, we connect a sensor to an implanted (but only partially resorbable) data-communication system, proving the principle that there is no need for any percutaneous wiring. The devices can be adapted to sense fluid flow, motion, pH or thermal characteristics, in formats that are compatible with the body's abdomen and extremities, as well as the deep brain, suggesting that the sensors might meet many needs in clinical medicine.

694 citations