Paul received his B.S. in Physics from The College of William & Mary in 2004, and his Ph.D. in Applied Physics from Stanford University in 2014.

Academic Appointments

  • Phys Sci Res Assoc, Edward L. Ginzton Laboratory

Current Research and Scholarly Interests

Paul studies computational design optimization for electron optics.

All Publications

  • Dielectrophoresis-assisted plasmonic trapping of dielectric nanoparticles PHYSICAL REVIEW A Zaman, M. A., Padhy, P., Hansen, P. C., Hesselink, L. 2017; 95 (2)
  • Adjoint method for estimating Jiles-Atherton hysteresis model parameters JOURNAL OF APPLIED PHYSICS Zaman, M. A., Hansen, P. C., Neustock, L. T., Padhy, P., Hesselink, L. 2016; 120 (9)

    View details for DOI 10.1063/1.4962153

    View details for Web of Science ID 000383978100014

  • Accurate adjoint design sensitivities for nano metal optics OPTICS EXPRESS Hansen, P., Hesselink, L. 2015; 23 (18): 23899-23923

    View details for DOI 10.1364/OE.23.023899

    View details for Web of Science ID 000362419900082

    View details for PubMedID 26368483

  • Fabrication and Operation of a Nano-Optical Conveyor Belt JOVE-JOURNAL OF VISUALIZED EXPERIMENTS Ryan, J., Zheng, Y., Hansen, P., Hesselink, L. 2015

    View details for DOI 10.3791/52842

    View details for PubMedID 26381708

  • Nano-Optical Conveyor Belt, Part II: Demonstration of Handoff Between Near-Field Optical Traps. Nano letters Zheng, Y., Ryan, J., Hansen, P., Cheng, Y., Lu, T., Hesselink, L. 2014; 14 (6): 2971-2976


    Optical tweezers have been widely used to manipulate biological and colloidal material, but the diffraction limit of far-field optics makes focused beams unsuitable for manipulating nanoscale objects with dimensions much smaller than the wavelength of light. While plasmonic structures have recently been successful in trapping nanoscale objects with high positioning accuracy, using such structures for manipulation over longer range has remained a significant challenge. In this work, we introduce a conveyor belt design based on a novel plasmonic structure, the resonant C-shaped engraving (CSE). We show how long-range manipulation is made possible by means of handoff between neighboring CSEs, and we present a simple technique for controlling handoff by rotating the polarization of laser illumination. We experimentally demonstrate handoff between a pair of CSEs for polystyrene spheres 200, 390, and 500 nm in diameter. We then extend this technique and demonstrate controlled particle transport down a 4.5 μm long "nano-optical conveyor belt."

    View details for DOI 10.1021/nl404045n

    View details for PubMedID 24807058

  • Nano-optical conveyor belt, part I: theory. Nano letters Hansen, P., Zheng, Y., Ryan, J., Hesselink, L. 2014; 14 (6): 2965-2970


    We propose a method for peristaltic transport of nanoparticles using the optical force field over a nanostructured surface. Nanostructures may be designed to produce strong near-field hot spots when illuminated. The hot spots function as optical traps, separately addressable by their resonant wavelengths and polarizations. By activating closely packed traps sequentially, nanoparticles may be handed off between adjacent traps in a peristaltic fashion. A linear repeating structure of three separately addressable traps forms a "nano-optical conveyor belt"; a unit cell with four separately addressable traps permits controlled peristaltic transport in the plane. Using specifically designed activation sequences allows particle sorting.

    View details for DOI 10.1021/nl404011s

    View details for PubMedID 24807203

  • Fundamentals of excitation and resonance of a Near-Field Transducer in the presence of a conductive magnetic recording medium Conference on Physics and Simulation of Optoelectronic Devices XX Piper, J. R., Hansen, P. C., Hesselink, L. SPIE-INT SOC OPTICAL ENGINEERING. 2012

    View details for DOI 10.1117/12.909477

    View details for Web of Science ID 000302993700017

  • Ultra-high resolution resonant C-shaped aperture nano-tip OPTICS EXPRESS Cheng, Y., Takashima, Y., Yuen, Y., Hansen, P. C., Leen, J. B., Hesselink, L. 2011; 19 (6): 5077-5085


    We report a new optical near-field transducer comprised of a metallic nano-antenna extending from the ridge of a C-shaped metallic nano-aperture. Finite-difference time domain simulations predict that the C-aperture nano-tip (CAN-Tip) provides high intensity (650x), high optical resolution (~λ/60), and background-free near-field illumination at a wavelength of 980 nm. The CAN-Tip has an aperture resonance and tip antenna resonance which may be tuned independently, so the structure can be made resonant at ultraviolet wavelengths without being unduly small. This near-field optical resolution of 16.1 nm has been experimentally confirmed by employing the CAN-Tip as an NSOM probe.

    View details for Web of Science ID 000288871300040

    View details for PubMedID 21445142

  • Nanophotonic Device Optimization with Adjoint FDTD Conference on Lasers and Electro-Optics (CLEO) Hansen, P., Zheng, Y., Perederey, E., Hesselink, L. IEEE. 2011
  • Near-field optical data storage using C-apertures APPLIED PHYSICS LETTERS Leen, J. B., Hansen, P., Cheng, Y., Gibby, A., Hesselink, L. 2010; 97 (7)

    View details for DOI 10.1063/1.3474801

    View details for Web of Science ID 000281153600075

  • Improved focused ion beam fabrication of near-field apertures using a silicon nitride membrane OPTICS LETTERS Leen, J. B., Hansen, P., Cheng, Y., Hesselink, L. 2008; 33 (23): 2827-2829


    We report an improved fabrication method for C-shaped near-field apertures resonant in the near-IR regime. The apertures are created in a metal layer on a silicon nitride membrane using a focused ion beam and a through membrane milling technique that avoids two problems with fabricating very small apertures: gallium contamination and edge rounding. Finite-difference time-domain simulations predict a 63x more intense near field with a 2.2x smaller spot versus conventionally milled apertures. We verify the position of the simulated resonance peaks with experimental far-field transmission measurements where we also find an increase of 8.8x in intensity. Our method has applications to many other plasmonic devices including bow-tie and fractal apertures, periodic arrays, and gratings.

    View details for Web of Science ID 000262206500035

    View details for PubMedID 19037440

  • Design of a subwavelength bent C-aperture waveguide OPTICS LETTERS Hansen, P., Hesselink, L., Leen, B. 2007; 32 (12): 1737-1739


    We present a design for a subwavelength C-shaped optical waveguide with a 90 degrees junction that efficiently transports light while maintaining tight confinement with an exit spot size of lambda/7. Finite-difference time-domain simulations of perfect electric conductors and Au C-aperture waveguides are performed for optical frequencies. A design resonant near 780 nm is presented, with a spot size of 107 nm x 107 nm and an energy density enhancement factor of 10 for a bent waveguide of total length 1.4 microm.

    View details for Web of Science ID 000248144600047

    View details for PubMedID 17572764

  • 90 degrees bent metallic waveguide with a tapered C-shaped aperture for use in HAMR Topical Meeting on Optical Data Storage Leen, J. B., Cho, E., Suh, S., Hansen, P. C., Sohn, J., Choa, S., Hesselink, L. SPIE-INT SOC OPTICAL ENGINEERING. 2007

    View details for DOI 10.1117/12.738908

    View details for Web of Science ID 000250199900017