467 results match your criteria Applied Physics Letters[Journal]

Constant amplitude driving of a radiofrequency excited plasmonic tunnel junction.

Appl Phys Lett 2021 May 11;118(19). Epub 2021 May 11.

Institute of Physics, Czech Academy of Sciences, Cukrovarnická 10/112, CZ16200 Praha 6, Czech Republic.

Constant-amplitude bias modulation over a broad range of microwave frequencies is a prerequisite for application in high-resolution spectroscopic techniques in a tunneling junction as e.g. electron spin resonance spectroscopy or optically detected paramagnetic resonance. Read More

View Article and Full-Text PDF

Ultrafast amplitude modulation for molecular and hemodynamic ultrasound imaging.

Appl Phys Lett 2021 Jun;118(24):244102

Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, USA.

Ultrasound is playing an emerging role in molecular and cellular imaging thanks to new micro- and nanoscale contrast agents and reporter genes. Acoustic methods for the selective detection of these imaging agents are needed to maximize their impact in biology and medicine. Existing ultrasound pulse sequences use the nonlinearity in contrast agents' response to acoustic pressure to distinguish them from mostly linear tissue scattering. Read More

View Article and Full-Text PDF

Measurements of acoustic radiation force of ultrahigh frequency ultrasonic transducers using model-based approach.

Appl Phys Lett 2021 May;118(18):184102

Department of Aerospace and Mechanical Engineering, University of Notre Dame, Notre Dame, Indiana 46556, USA.

Even though ultrahigh frequency ultrasonic transducers over 60 MHz have been used for single-cell-level manipulation such as intracellular delivery, acoustic tweezers, and stimulation to investigate cell phenotype and cell mechanics, no techniques have been available to measure the actual acoustic radiation force (ARF) applied to target cells. Therefore, we have developed an approach to measure the ARF of ultrahigh frequency ultrasonic transducers using a theoretical model of the dynamics of a solid sphere in a gelatin phantom. To estimate ARF at the focus of a 130 MHz transducer, we matched measured maximum displacements of a solid sphere with theoretical calculations. Read More

View Article and Full-Text PDF

Optical coherence viscometry.

Appl Phys Lett 2021 Apr 20;118(16):164102. Epub 2021 Apr 20.

Department of Radiology, Mayo Clinic, Rochester, Minnesota 55905, USA.

We report a technique, named optical coherence viscometry (OCV), to measure the viscosity of Newtonian fluids in a noncontact manner. According to linear wave theory with small amplitudes, capillary waves are associated with fluid mechanical properties. To perform this measurement and avoid the overdamped effects of capillary waves in viscous fluids, transient acoustic radiation force was applied to generate capillary waves. Read More

View Article and Full-Text PDF

Ultrasound differential phase contrast using backscattering and the memory effect.

Appl Phys Lett 2021 Mar 26;118(12):124103. Epub 2021 Mar 26.

Department of Biomedical Engineering, Boston University, Boston Massachusetts 02215, USA.

We describe a simple and fast technique to perform ultrasound differential phase contrast (DPC) imaging in arbitrarily thick scattering media. Although configured in a reflection geometry, DPC is based on transmission imaging and is a direct analog of optical differential interference contrast. DPC exploits the memory effect and works in combination with standard pulse-echo imaging, with no additional hardware or data requirements, enabling complementary phase contrast (in the transverse direction) without any need for intensive numerical computation. Read More

View Article and Full-Text PDF

High-speed label-free two-photon fluorescence microscopy of metabolic transients during neuronal activity.

Appl Phys Lett 2021 Feb 23;118(8):081104. Epub 2021 Feb 23.

Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA.

The brain is an especially active metabolic system, requiring a large supply of energy following neuronal activation. However, direct observation of cellular metabolic dynamics associated with neuronal activation is challenging with currently available imaging tools. In this study, an optical imaging approach combining imaging of calcium transients and the metabolic co-enzyme nicotinamide adenine dinucleotide (phosphate) (NAD(P)H) is utilized to track the metabolic dynamics in hippocampal neuron cultures. Read More

View Article and Full-Text PDF
February 2021

Ultra-compact visible light depolarizer based on dielectric metasurface.

Appl Phys Lett 2020 4;116(5):0511031-511035. Epub 2020 Feb 4.

National Laboratory of Solid State Microstructures, College of Engineering and Applied Sciences and Collaborative Innovation Center of Advanced Microstructures, Nanjing University 210093, China.

With rapid development towards shrinking the size of traditional photonic systems such as cameras, spectrometers, displays and illumination systems, there is an urgent need for high performance and ultra-compact functional optical elements. The large footprint of traditional bulky optical elements, their monofunctional response and the inability for direct integration into nanophotonic devices have severely limited progress in this area. Metasurfaces, consisting of an array of subwavelength nanoscatterers with spatially varying geometries, have shown remarkable performance as ultrathin multifunctional optical elements. Read More

View Article and Full-Text PDF
February 2020

The effect of surface roughness on laser-induced stress wave propagation.

Appl Phys Lett 2020 Sep 24;117(12):121601. Epub 2020 Sep 24.

Department of Mechanical Engineering, University of Kentucky, Lexington, Kentucky 40506, USA.

We investigate laser-induced acoustic wave propagation through smooth and roughened titanium-coated glass substrates. Acoustic waves are generated in a controlled manner via the laser spallation technique. Surface displacements are measured during stress wave loading by the alignment of a Michelson-type interferometer. Read More

View Article and Full-Text PDF
September 2020

Nonlinear losses in magnon transport due to four-magnon scattering.

Appl Phys Lett 2020 ;117(4)

Institut für Ionenstrahlphysik und Materialforschung, Helmholtz-Zentrum Dresden-Rossendorf, D-01328 Dresden, Germany.

We report on the impact of nonlinear four-magnon scattering on magnon transport in microstructured CoFe waveguides with low magnetic damping. We determine the magnon propagation length with microfocused Brillouin light scattering over a broad range of excitation powers and detect a decrease of the attenuation length at high powers. This is consistent with the onset of nonlinear four-magnon scattering. Read More

View Article and Full-Text PDF
January 2020

Ultraminiature AlN diaphragm acoustic transducer.

Appl Phys Lett 2020 Oct;117(14):143504

Singular Medical USA, Irvine, California 92614, USA.

Piezoelectric acoustic transducers consisting of a circular aluminum nitride and silicon nitride unimorph diaphragm and an encapsulated air-filled back cavity are reported. Analytical and finite element analysis models are used to design the transducer to achieve low minimum detectable pressure (MDP) within chosen size restrictions. A series of transducers with varying radii are fabricated using microelectromechanical systems (MEMS) techniques. Read More

View Article and Full-Text PDF
October 2020

Enhancing sensitivity of lateral flow assay with application to SARS-CoV-2.

Appl Phys Lett 2020 Sep;117(12):120601

Texas A&M University, College Station, Texas 77843, USA.

Lateral flow assay (LFA) has long been used as a biomarker detection technique. It has advantages such as low cost, rapid readout, portability, and ease of use. However, its qualitative readout process and lack of sensitivity are limiting factors. Read More

View Article and Full-Text PDF
September 2020

A predictive model of the temperature-dependent inactivation of coronaviruses.

Appl Phys Lett 2020 Aug;117(6):060601

Department of Mechanical Engineering, Rice University, 6100 Main Street, Houston, Texas 77005, USA.

The COVID-19 pandemic has stressed healthcare systems and supply lines, forcing medical doctors to risk infection by decontaminating and reusing single-use personal protective equipment. The uncertain future of the pandemic is compounded by limited data on the ability of the responsible virus, SARS-CoV-2, to survive across various climates, preventing epidemiologists from accurately modeling its spread. However, a detailed thermodynamic analysis of experimental data on the inactivation of SARS-CoV-2 and related coronaviruses can enable a fundamental understanding of their thermal degradation that will help model the COVID-19 pandemic and mitigate future outbreaks. Read More

View Article and Full-Text PDF

Transcranial focused ultrasound generates skull-conducted shear waves: Computational model and implications for neuromodulation.

Appl Phys Lett 2020 Jul 24;117(3):033702. Epub 2020 Jul 24.

Division of Engineering and Applied Science, California Institute of Technology, Pasadena, California 91125, USA.

Focused ultrasound (FUS) is an established technique for non-invasive surgery and has recently attracted considerable attention as a potential method for non-invasive neuromodulation. While the pressure waves in FUS procedures have been extensively studied in this context, the accompanying shear waves are often neglected due to the relatively high shear compliance of soft tissues. However, in bony structures such as the skull, acoustic pressure can also induce significant shear waves that could propagate outside the ultrasound focus. Read More

View Article and Full-Text PDF

Silicon carbide zipper photonic crystal optomechanical cavities.

Appl Phys Lett 2020 Jun 3;116(22):221104. Epub 2020 Jun 3.

Department of Electrical and Computer Engineering, University of Rochester, Rochester, New York 14627, USA.

We demonstrate a silicon carbide (SiC) zipper photonic crystal optomechanical cavity. The device is on a 3C-SiC-on-silicon platform and has a compact footprint of ∼30 × 1 m. The device shows an optical quality of 2800 at telecom and a mechanical quality of 9700 at 12 MHz with an effective mass of ∼3. Read More

View Article and Full-Text PDF

Upper limit for angular compounding speckle reduction.

Appl Phys Lett 2019 May 28;114(21):211101. Epub 2019 May 28.

Angular compounding is a technique for reducing speckle noise in optical coherence tomography that is claimed to significantly improve the signal-to-noise ratio (SNR) of images without impairing their spatial resolution. Here, we examine how focal point movements caused by optical aberrations in an angular compounding system may produce unintended spatial averaging and concomitant loss of spatial resolution. Experimentally, we accounted for such aberrations by aligning our system and measuring distortions in images and found that when the distortions were corrected, the speckle reduction by angular compounding was limited. Read More

View Article and Full-Text PDF

Perspectives on high resolution microvascular imaging with contrast ultrasound.

Appl Phys Lett 2020 May;116(21):210501

The Joint Department of Biomedical Engineering, The University of North Carolina at Chapel Hill and North Carolina State University, Campus Box 7575, Chapel Hill, North Carolina 27599, USA.

Recent developments in contrast enhanced ultrasound have demonstrated a potential to visualize small blood vessels , unlike anything possible with traditional grayscale ultrasound. This Perspective article introduces microvascular imaging strategies and their underlying technology. Read More

View Article and Full-Text PDF

Changes in microbubble dynamics upon adhesion to a solid surface.

Appl Phys Lett 2020 Mar 24;116(12):123703. Epub 2020 Mar 24.

Department of Chemical and Biological Engineering, University of Colorado, Boulder, Colorado 80309, USA.

The interaction between an acoustically driven microbubble and a surface is of interest for a variety of applications, such as ultrasound imaging and therapy. Prior investigations have mainly focused on acoustic effects of a rigid boundary, where it was generally observed that the wall increases inertia and reduces the microbubble resonance frequency. Here we investigate the response of a lipid-coated microbubble adherent to a rigid wall. Read More

View Article and Full-Text PDF

Super-shear evanescent waves for non-contact elastography of soft tissues.

Appl Phys Lett 2019 Aug 21;115(8):083701. Epub 2019 Aug 21.

Department of Bioengineering, University of Washington, Seattle, Washington 98195, USA.

We describe surface wave propagation in soft elastic media at speeds exceeding the bulk shear wave speed. By linking these waves to the elastodynamic Green's function, we derive a simple relationship to quantify the elasticity of a soft medium from the speed of this supershear evanescent wave (SEW). We experimentally probe SEW propagation in tissue-mimicking phantoms, human cornea , and skin using a high-speed optical coherence elastography system. Read More

View Article and Full-Text PDF

Engineering the gain-bandwidth product of phototransistor diodes.

Appl Phys Lett 2019 Jul 30;115(5):051104. Epub 2019 Jul 30.

Bio-Inspired Sensors and Optoelectronics Laboratory, Northwestern University, 2145 Sheridan Rd, Evanston, Illinois 60208, USA.

In recent years, phototransistors have considerably expanded their field of application, including for instance heterodyne detection and optical interconnects. Unlike in low-light imaging, some of these applications require fast photodetectors that can operate in relatively high light levels. Since the gain and bandwidth of phototransistors are not constant across different optical powers, the devices that have been optimized for operation in low light level cannot effectively be employed in different technological applications. Read More

View Article and Full-Text PDF

Viscoelastic second normal stress difference dominated multiple-stream particle focusing in microfluidic channels.

Appl Phys Lett 2019 Dec 24;115(26):263702. Epub 2019 Dec 24.

Center of Excellence for Biomedical Microfluidics, Department of Mechanical Engineering, University of Utah, Salt Lake City, Utah 84112, USA.

Particle focusing in viscoelastic fluid flow is a promising approach for inducing particle separations in microfluidic devices. The results from theoretical studies indicated that multiple stream particle focusing can be realized with a large magnitude of the elastic second normal stress difference (N). For dilute polymer solutions, theoretical and experimental studies show that the magnitude of N is never large, no matter how large the polymer molecular weight nor how high the shear rate. Read More

View Article and Full-Text PDF
December 2019

Accurate phase retrieval of complex 3D point spread functions with deep residual neural networks.

Appl Phys Lett 2019 Dec 18;115(25):251106. Epub 2019 Dec 18.

Department of Chemistry, Stanford University, Stanford, California 94305, USA.

Phase retrieval, i.e., the reconstruction of phase information from intensity information, is a central problem in many optical systems. Read More

View Article and Full-Text PDF
December 2019

Laser-driven semiconductor switch for generating nanosecond pulses from a megawatt gyrotron.

Appl Phys Lett 2019 Apr 24;114(16):164102. Epub 2019 Apr 24.

Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.

A laser-driven semiconductor switch (LDSS) employing silicon (Si) and gallium arsenide (GaAs) wafers has been used to produce nanosecond-scale pulses from a 3 s, 110 GHz gyrotron at the megawatt power level. Photoconductivity was induced in the wafers using a 532 nm laser, which produced 6 ns, 230 mJ pulses. Irradiation of a single Si wafer by the laser produced 110 GHz RF pulses with a 9 ns width and >70% reflectance. Read More

View Article and Full-Text PDF

Understanding Photovoltaic Energy Losses under Indoor Lighting Conditions.

Appl Phys Lett 2020 ;117(4)

Engineering Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA.

The external luminescence quantum yield as a function of the solar cell current density when exposed to low indoor light was estimated based on absolute electroluminescence measurements and a self-consistent use of the electro-optical reciprocity relationship. By determining the luminescence yield at current densities corresponding to the cell operation at the maximum power point, we can compute energy losses corresponding to radiative and nonradiative recombination. Combined with other major energy losses, we can obtain a clear picture of the fundamental balance of energy within the cell when exposed to room light with a typical total illuminance of 1000 lx or less. Read More

View Article and Full-Text PDF
January 2020

Low Gilbert damping and high thermal stability of Ru-seeded L1-phase FePd perpendicular magnetic thin films at elevated temperatures.

Appl Phys Lett 2020 ;117(8)

Department of Mechanical Engineering, University of Minnesota, Minneapolis, MN 55455 USA.

Bulk perpendicular magnetic anisotropy materials are proposed to be a promising candidate for next-generation ultrahigh density and ultralow energy-consumption spintronic devices. In this work, we experimentally investigate the structure, thermal stability, and magnetic properties of FePd thin films seeded by a Ru layer. An -phase Ru layer induces the highly-ordered L1-phase FePd thin films with perpendicular magnetic anisotropy ( ~ 10. Read More

View Article and Full-Text PDF
January 2020

Dual-polarization analog optical phase conjugation for focusing light through scattering media.

Appl Phys Lett 2019 Jun 13;114(23):231104. Epub 2019 Jun 13.

Caltech Optical Imaging Laboratory, Andrew and Peggy Cherng Department of Medical Engineering, Department of Electrical Engineering, California Institute of Technology, Pasadena, California 91125, USA.

Focusing light through or inside scattering media by the analog optical phase conjugation (AOPC) technique based on photorefractive crystals (PRCs) has been intensively investigated due to its high controlled degrees of freedom and short response time. However, the existing AOPC systems only phase-conjugate the scattered light in one polarization direction, while the polarization state of light scattered through a thick scattering medium is spatially random in general, which means that half of the scattering information is lost. Here, we propose dual-polarization AOPC for focusing light through scattering media to improve the efficiency and fidelity in the phase conjugation. Read More

View Article and Full-Text PDF

Numerical modeling of ultrasound heating for the correction of viscous heating artifacts in soft tissue temperature measurements.

Appl Phys Lett 2019 May 21;114(20):203702. Epub 2019 May 21.

Department of Biomedical Engineering, Columbia University, New York, New York 10032, USA.

Measuring temperature during focused ultrasound (FUS) procedures is critical for characterization, calibration, and monitoring to ultimately ensure safety and efficacy. Despite the low cost and the high spatial and temporal resolutions of temperature measurements using thermocouples, the viscous heating (VH) artifact at the thermocouple-tissue interface requires reading corrections for correct thermometric analysis. In this study, a simulation pipeline is proposed to correct the VH artifact arising from temperature measurements using thermocouples in FUS fields. Read More

View Article and Full-Text PDF

A directional fibre optic ultrasound transmitter based on a reduced graphene oxide and polydimethylsiloxane composite.

Appl Phys Lett 2019 Mar 21;114(11):113505. Epub 2019 Mar 21.

Strongly directional ultrasound sources are desirable for many minimally invasive applications, as they enable high-quality imaging in the presence of positioning uncertainty. All-optical ultrasound is an emerging paradigm that exhibits high frequencies, large bandwidths, and a strong miniaturisation potential. Here, we report the design, modelling, and fabrication of a highly directional fibre-optic ultrasound transmitter that uses a composite of reduced graphene oxide and polydimethylsiloxane as the optical ultrasound generator. Read More

View Article and Full-Text PDF

High spin-wave propagation length consistent with low damping in a metallic ferromagnet.

Appl Phys Lett 2019 ;115(12)

Walther-Meißner Institute, Bayerische Akademie der Wissenschaften, 85748 Garching, Germany.

We report ultralow intrinsic magnetic damping in CoFe heterostructures, reaching the low 10 regime at room temperature. By using a broadband ferromagnetic resonance technique in out-of-plane geometry, we extracted the dynamic magnetic properties of several CoFebased heterostructures with varying ferromagnetic layer thicknesses. By measuring radiative damping and spin pumping effects, we found the intrinsic damping of a 26 nm thick sample to be ≲ 3. Read More

View Article and Full-Text PDF
January 2019

Capturing magnetic bead-based arrays using perpendicular magnetic anisotropy.

Appl Phys Lett 2019 ;115(8)

Mechanical and Aerospace Engineering Department, University of California, Los Angeles, Los Angeles, California 90095, USA.

Designing and implementing means of locally trapping magnetic beads and understanding the factors underlying the bead capture force are important steps toward advancing the capture-release process of magnetic particles for biological applications. In particular, capturing magnetically labeled cells using magnetic microstructures with perpendicular magnetic anisotropy (PMA) will enable an approach to cell manipulation for emerging lab-on-a-chip devices. Here, a Co (0. Read More

View Article and Full-Text PDF
January 2019

The effect of luminescent coupling on modulated photocurrent measurements in multijunction solar cells.

Appl Phys Lett 2019 ;115(8)

Engineering Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA.

Luminescent coupling in multijunction solar cells has a major impact on device response, and its impact on current-voltage and quantum efficiency measurements is well established. However, the role of luminescent coupling in more advanced characterization techniques such as modulated photocurrent spectroscopy is virtually unknown. Here we present measurements of the frequency-dependent photocurrent of a triple junction solar cell with significant coupling between adjacent junctions. Read More

View Article and Full-Text PDF
January 2019