Dr. Ashwin Sampathkumar Profile

Dr. Ashwin Sampathkumar

Director of Optics and Photonics Research at Riverside Research

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Publications (14)

Proceedings Article | 1 May 2017 Presentation + Paper

Extraction and validation of algorithms based on analog side-channels

Ronald Riley, James Graham, Ryan Fuller, Rusty Baldwin, Ashwin Sampathkumar

Proceedings Volume 10185, 1018506 (2017) https://doi.org/10.1117/12.2262113

KEYWORDS: Internet, Analog electronics, Signal processing, Principal component analysis, Network security, Machine learning, Acoustics, Signal to noise ratio, Infrared signatures, Surface plasmons, Calibration, Clocks, Interference (communication)

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Proceedings Article | 1 May 2017 Presentation + Paper

Characterization of Riscure 1-GHz low sensitivity probe for side channel analysis (SCA)

James Graham, Rusty Baldwin, Ashwin Sampathkumar

Proceedings Volume 10185, 1018507 (2017) https://doi.org/10.1117/12.2262121

KEYWORDS: Amplifiers, Oscilloscopes, Analytical research, 3D scanning, Electronic components, Clocks, Receivers, Transmitters, Antennas, Analog electronics, Signal attenuation

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Proceedings Article | 21 May 2015 Paper

Remote characterization of biological specimens using all-optical frequency-domain photoacoustic microscopy

Ashwin Sampathkumar

Proceedings Volume 9487, 94870H (2015) https://doi.org/10.1117/12.2177426

KEYWORDS: Tissue optics, Modulation, Tissues, Optical amplifiers, Transducers, Signal detection, Geometrical optics, Photoacoustic spectroscopy, Acoustics, Biomedical optics

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Proceedings Article | 13 May 2015 Paper

3D noninvasive, high-resolution imaging using a photoacoustic tomography (PAT) system and rapid wavelength-cycling lasers

Ashwin Sampathkumar, Daniel Gross, Marc Klosner, Gary Chan, Chunbai Wu, Donald Heller

Proceedings Volume 9487, 94870I (2015) https://doi.org/10.1117/12.2177602

KEYWORDS: Breast, Acquisition tracking and pointing, Imaging systems, Tissue optics, Tumors, 3D modeling, Breast cancer, Transducers, Absorption, Tissues

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Proceedings Article | 20 March 2015 Paper

Optical characterization of vitreous structure in health and disease

Ashwin Sampathkumar, Matin Khoshnevis, Jeffrey Ketterling, Jerry Sebag

Proceedings Volume 9307, 930714 (2015) https://doi.org/10.1117/12.2080543

KEYWORDS: Vitreous, Scattering, Gold, Light scattering, Opacity, Nanoparticles, Optical spheres, Spherical lenses, Absorption, Spectroscopy

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Patients with myopic vitreopathy (MV) and posterior vitreous detachment (PVD) see floaters, which often can degrade contrast sensitivity to a significant extent. The floaters are associated with irregularly shaped vitreous opacities. In contrast, asteroid hyalosis (AH), which is characterized by microscopic, spherical, white asteroid bodies (ABs) that move with vitreous displacement during eye movements, does not interfere significantly with vision. We hypothesize that the irregular surface of vitreous opacities associated with MV distinguish MV from AH and its smooth-surfaced ABs. A finite-element model was developed to characterize the light-scattering field of vitreous opacities in MV and AH. Vitreous opacities were modeled as spherical bodies and illuminated by a plane wave of light in the optical wavelength of 400-1000 nm. The model has provisions to add random perturbations to the spherical surfaces to vary light-scattering properties and mimic disturbances in vision from simple diffraction rings to more-complex patterns. Samples of ex vivo porcine vitreous (0.4-0.5 ml) were placed in a custom spectrophotometer and the static, light-scattering field of the sample was measured in the spectral range of 400-1000 nm with a resolution of 0.3 nm. Model solutions mimicking healthy vitreous and AH were experimentally validated using a laboratory optical apparatus. Model-based estimates of scattering cross-sections of calibrated gold nanoparticles were found to be in good agreement with experimental measurements. Simulation results potentially can complement experimental data to quantitatively characterize vitreous opacities and distinguish between structures that significantly impact vision, such as those due to myopic vitreopathy and aging, from those that have little impact, like ABs. Such techniques to determine the structural significance of vitreous opacification would be very useful in selecting patients for surgery as well as evaluating the efficacy of experimental therapies for floaters.

Proceedings Article | 11 March 2015 Paper

Quantitative photoacoustic assessment of ex-vivo lymph nodes of colorectal cancer patients

Ashwin Sampathkumar, Jonathan Mamou, Emi Saegusa-Beercroft, Parag Chitnis, Junji Machi, Ernest Feleppa

Proceedings Volume 9323, 93231T (2015) https://doi.org/10.1117/12.2079961

KEYWORDS: Photoacoustic spectroscopy, Lymphatic system, Tissue optics, Tissues, Colorectal cancer, Ultrasonography, Statistical analysis, Transducers, Cancer, Image processing

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Staging of cancers and selection of appropriate treatment requires histological examination of multiple dissected lymph nodes (LNs) per patient, so that a staggering number of nodes require histopathological examination, and the finite resources of pathology facilities create a severe processing bottleneck. Histologically examining the entire 3D volume of every dissected node is not feasible, and therefore, only the central region of each node is examined histologically, which results in severe sampling limitations. In this work, we assess the feasibility of using quantitative photoacoustics (QPA) to overcome the limitations imposed by current procedures and eliminate the resulting under sampling in node assessments. QPA is emerging as a new hybrid modality that assesses tissue properties and classifies tissue type based on multiple estimates derived from spectrum analysis of photoacoustic (PA) radiofrequency (RF) data and from statistical analysis of envelope-signal data derived from the RF signals. Our study seeks to use QPA to distinguish cancerous from non-cancerous regions of dissected LNs and hence serve as a reliable means of imaging and detecting small but clinically significant cancerous foci that would be missed by current methods. Dissected lymph nodes were placed in a water bath and PA signals were generated using a wavelength-tunable (680-950 nm) laser. A 26-MHz, f-2 transducer was used to sense the PA signals. We present an overview of our experimental setup; provide a statistical analysis of multi-wavelength classification parameters (mid-band fit, slope, intercept) obtained from the PA signal spectrum generated in the LNs; and compare QPA performance with our established quantitative ultrasound (QUS) techniques in distinguishing metastatic from non-cancerous tissue in dissected LNs. QPA-QUS methods offer a novel general means of tissue typing and evaluation in a broad range of disease-assessment applications, e.g., cardiac, intravascular, musculoskeletal, endocrine-gland, etc.

Proceedings Article | 11 March 2015 Paper

Advanced laser systems for photoacoustic imaging

Marc Klosner, Ashwin Sampathkumar, Gary Chan, Chunbai Wu, Daniel Gross, Donald Heller

Proceedings Volume 9323, 932349 (2015) https://doi.org/10.1117/12.2077780

KEYWORDS: Acquisition tracking and pointing, Tissues, Ultrasonography, Imaging systems, Breast, Laser systems engineering, Mammography, Diagnostics, Alexandrite lasers, Magnetic resonance imaging

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Proceedings Article | 24 February 2015 Paper

All-optical photoacoustic imaging and detection of early-stage dental caries

Ashwin Sampathkumar, David Hughes, Chris Longbottom, Katherine Kirk

Proceedings Volume 9306, 93060E (2015) https://doi.org/10.1117/12.2079765

KEYWORDS: Teeth, Dental caries, Signal detection, Ultrasonography, Tissues, Reconstruction algorithms, Photoacoustic imaging, Pulsed laser operation, Absorption, Nd:YAG lasers

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Proceedings Article | 25 June 2014 Paper

Multiplexed optical operation of nanoelectromechanical systems (NEMS) arrays for sensing and signal-processing applications

Ashwin Sampathkumar

Proceedings Volume 9083, 90832Z (2014) https://doi.org/10.1117/12.2053397

KEYWORDS: Nanoelectromechanical systems, Resonators, Multiplexing, Sensors, Modulation, Photoresist materials, Charge-coupled devices, Electronics, Silicon, Beam shaping

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NEMS are rapidly being developed for a variety of sensing applications as well as for exploring interesting regimes in fundamental physics. In most of these endeavors, operation of a NEMS device involves actuating the device harmonically around its fundamental resonance and detecting subsequent motion while the device interacts with its environment. Even though a single NEMS resonator is exceptionally sensitive, a typical application, such as sensing or signal processing, requires the detection of signals from many resonators distributed over the surface of a chip. Therefore, one of the key technological challenges in the field of NEMS is development of multiplexed measurement techniques to detect the motion of a large number of NEMS resonators simultaneously. In this work, we address the important and difficult problem of interfacing with a large number of NEMS devices and facilitating the use of such arrays in, for example, sensing and signal processing applications. We report a versatile, all-optical technique to excite and read-out a distributed NEMS array. The NEMS array is driven by a distributed, intensity-modulated, optical pump through the photothermal effect. The ensuing vibrational response of the array is multiplexed onto a single, probe beam as a high-frequency phase modulation. The phase modulation is optically down converted to a low-frequency, intensity modulation using an adaptive full -field interferometer, and subsequently is detected using a charge-coupled device (CCD) array. Rapid and single-step mechanical characterization of approximately 60 nominally identical, high-frequency resonators is demonstrated. The technique may enable sensitivity improvements over single NEMS resonators by averaging signals coming from a multitude of devices in the array. In addition, the diffraction-limited spatial resolution may allow for position-dependent read-out of NEMS sensor chips for sensing multiple analytes or spatially inhomogeneous forces.

Proceedings Article | 28 May 2014 Paper

Ultra-broadband high-resolution photoacoustic / photothermal microscopy system for material characterization

Ashwin Sampathkumar

Proceedings Volume 9110, 91100L (2014) https://doi.org/10.1117/12.2053405

KEYWORDS: Modulation, Nanoelectromechanical systems, Aluminum, Microscopy, Material characterization, Tissue optics, Photoacoustic spectroscopy, Thin films, Acoustics

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Proceedings Article | 22 May 2014 Paper

High-resolution all-optical photoacoustic imaging system for remote interrogation of biological specimens

Ashwin Sampathkumar

Proceedings Volume 9107, 91071B (2014) https://doi.org/10.1117/12.2053412

KEYWORDS: Tissue optics, Teeth, Signal detection, Acoustics, Laser beam diagnostics, Lymphatic system, Photoacoustic spectroscopy, Transducers, Pulsed laser operation, Reconstruction algorithms

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Proceedings Article | 17 March 2014 Paper

Optical characterization of ex-vivo axillary lymph nodes of breast-cancer patients using a custom-built spectrophotometer

Ashwin Sampathkumar, Emi Saegusa-Beecroft, Jonathan Mamou, Parag Chitnis, Junji Machi, Ernest Feleppa

Proceedings Volume 8940, 89400Q (2014) https://doi.org/10.1117/12.2037864

KEYWORDS: Lymphatic system, Tissue optics, Spectrophotometry, Cancer, Photoacoustic spectroscopy, Optical properties, Pathology, Absorption, Optical testing, Spectroscopy

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Proceedings Article | 3 March 2014 Paper

All-optical photoacoustic microscopy (AOPAM) system for remote characterization of biological tissues

Ashwin Sampathkumar, Parag Chitnis, Ronald Silverman

Proceedings Volume 8943, 89432Y (2014) https://doi.org/10.1117/12.2038240

KEYWORDS: Tissues, Tissue optics, Signal detection, Laser beam diagnostics, Natural surfaces, Biomedical optics, Reconstruction algorithms, Photoacoustic microscopy, Acoustics, Transducers

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Proceedings Article | 3 March 2014 Paper

Spectrum analysis of photoacoustic signals for tissue classification

Parag Chitnis, Jonathan Mamou, Ashwin Sampathkumar, Ernest Feleppa

Proceedings Volume 8943, 89432J (2014) https://doi.org/10.1117/12.2037929

KEYWORDS: Particles, Tissue optics, Photoacoustic spectroscopy, Transducers, Optical spheres, Ultrasonography, Data acquisition, Spectrum analysis, Tissues, Signal analyzers

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Showing 5 of 14 publications

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