About

Professor Robert L. Byer is the William R. Kenan, Jr., Chair Professor of Applied Physics and a Professor of Photon Science at Stanford University. His research areas include Atomic, Molecular, & Optical Physics. As a faculty member at Stanford, he is involved in advancing knowledge and education in applied physics and photon science, contributing to the university's academic and research missions.

Research topics

• Computer Science
• Telecommunications
• Operating system
• Physics
• Astronomy

Selected publications

• Dielectric laser accelerators: photonic control, electron compression, and quantum sensing

  2024-01-01

  article

  We discuss how photonic control addresses key challenges of dielectric laser accelerators (DLAs) and propose applications using DLAs, i.e., electron pulse compression and quantum sensing of two-level systems.

  PublisherDOI

• Subrelativistic Alternating Phase Focusing Dielectric Laser Accelerators

  Physical Review Letters · 2024-02-23 · 17 citations

  article

  We demonstrate a silicon-based electron accelerator that uses laser optical near fields to both accelerate and confine electrons over extended distances. Two dielectric laser accelerator (DLA) designs were tested, each consisting of two arrays of silicon pillars pumped symmetrically by pulse front tilted laser beams, designed for average acceleration gradients 35 and 50 MeV/m, respectively. The DLAs are designed to act as alternating phase focusing (APF) lattices, where electrons, depending on the electron-laser interaction phase, will alternate between opposing longitudinal and transverse focusing and defocusing forces. By incorporating fractional period drift sections that alter the synchronous phase between ±60° off crest, electrons captured in the designed acceleration bucket experience half the peak gradient as average gradient while also experiencing strong confinement forces that enable long interaction lengths. We demonstrate APF accelerators with interaction lengths up to 708 μm and energy gains up to 23.7±1.07 keV FWHM, a 25% increase from starting energy, demonstrating the ability to achieve substantial energy gains with subrelativistic DLA.

  PublisherDOI

• Tunable infrared source employing Raman mixing

  OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information) · 2023-01-23

  otherOpen access1st authorCorresponding

  A tunable source of infrared radiation is obtained by irradiating an assemblage of Raman active gaseous atoms or molecules with a high intensity pumping beam of coherent radiation at a pump frequency .omega..sub.p to stimulate the generation of Stokes wave energy at a Stokes frequency .omega..sub.s and to stimulate the Raman resonant mode at the Raman mode frequency .omega..sub.R within the irradiated assemblage where the pump frequency .omega..sub.p minus the Stokes frequency .omega..sub.s is equal to the Raman mode frequency .omega..sub.R. The stimulated assemblage is irradiated with a tunable source of coherent radiation at a frequency .omega..sub.i to generate the output infrared radiation of the frequency .omega..sub.0 which is related to the Raman mode frequency .omega..sub.R and the input wave .omega..sub.i by the relation .omega..sub.0 =.omega..sub.i .+-..omega..sub.R. In one embodiment the interaction between the pump wave energy .omega..sub.p and the tunable input wave energy .omega..sub.i is collinear and the ratio of the phase velocity mismatch factor .DELTA.k to the electric field exponential gain coefficient T is within the range of 0.1 to 5. In another embodiment the pump wave energy .omega..sub.p and the tunable input wave energy .omega..sub.i have velocity vectors k.sub.p and k.sub.i which cross at an angle to each other to compensate for phase velocity mismatches in the medium. In another embodiment, the Stokes wave energy .omega..sub.s is generated by pump energy .omega..sub.p in a first Raman cell and .omega..sub.s, .omega..sub.i and .omega..sub.p are combined in a second Raman mixing cell to produce the output at .omega..sub.i.

  PublisherOA PDF

• Subrelativistic Alternating Phase Focusing Dielectric Laser Accelerators

  arXiv (Cornell University) · 2023-10-03 · 2 citations

  preprintOpen access

  We demonstrate a silicon-based electron accelerator that uses laser optical near fields to both accelerate and confine electrons over extended distances. Two dielectric laser accelerator (DLA) designs were tested, each consisting of two arrays of silicon pillars pumped symmetrically by pulse front tilted laser beams, designed for average acceleration gradients 35 and 50 MeV/m respectively. The DLAs are designed to act as alternating phase focusing (APF) lattices, where electrons, depending on the electron-laser interaction phase, will alternate between opposing longitudinal and transverse focusing and defocusing forces. By incorporating fractional period drift sections that alter the synchronous phase between $\pm 60^\circ$ off crest, electrons captured in the designed acceleration bucket experience half the peak gradient as average gradient while also experiencing strong confinement forces that enable long interaction lengths. We demonstrate APF accelerators with interaction lengths up to 708 $μ$m and energy gains up to 23.7 $\pm$ 1.07 keV FWHM, a 25$\%$ increase from starting energy, demonstrating the ability to achieve substantial energy gains with subrelativistic DLA.

  PublisherOA PDFDOI

• Miniature light-driven nanophotonic electron acceleration and control

  Advances in Optics and Photonics · 2022-10-05 · 34 citations

  articleCorresponding

  Dielectric laser accelerators (DLAs) are fundamentally based on the interaction of photons with free electrons, where energy and momentum conservation are satisfied by mediation of a nanostructure. In this scheme, the photonic nanostructure induces near-fields which transfer energy from the photon to the electron, similar to the inverse-Smith–Purcell effect described in metallic gratings. This, in turn, may provide ground-breaking applications, as it is a technology promising to miniaturize particle accelerators down to the chip scale. This fundamental interaction can also be used to study and demonstrate quantum photon-electron phenomena. The spontaneous and stimulated Smith–Purcell effect and the photon-induced near-field electron-microscopy (PINEM) effect have evolved to be a fruitful ground for observing quantum effects. In particular, the energy spectrum of the free electron has been shown to have discrete energy peaks, spaced with the interacting photon energy. This energy spectrum is correlated to the photon statistics and number of photon exchanges that took place during the interaction. We give an overview of DLA and PINEM physics with a focus on electron phase-space manipulation.

  PublisherDOI

• Electron Pulse Compression with Optical Beat Note

  Conference on Lasers and Electro-Optics · 2022-01-01

  articleCorresponding

  We propose to use optical beat notes to compress electron pulses, which is applicable to electron pulses with a wide range of initial duration.

  PublisherDOI

• Ultra-bright Coherent Undulator Radiation Driven by Dielectric Laser Accelerator

  arXiv (Cornell University) · 2022-08-08

  preprintOpen accessSenior author

  A dielectric laser accelerator, operating at optical frequencies and GHz pulse rate, is expected to produce attosec electron bunches with a moderate beam current at high energy. For relativistic electrons, the attosec bunch has a spatial length of a few nanometers, which is well suited for generating high-brightness superradiance in the VUV, EUV, and x-ray spectra. Our study shows that the brilliance of coherent undulator radiation driven by a short-bunch beam with 1~10 fC bunch charge from a dielectric laser accelerator is comparable to or higher than that of a synchrotron in the 0.1 ~ 3 keV photon energy range, even though the beam power of the dielectric laser accelerator is about a million times lower than that of a synchrotron. When the brilliance under comparison is normalized to the electron beam power, the proposed coherent undulator radiation source becomes the brightest source on earth across the whole VUV, EUV, and soft x-ray spectrum.

  PublisherOA PDFDOI

• Microchip accelerators

  Physics Today · 2021-08-01 · 7 citations

  articleOpen accessSenior author

  An international collaboration aims to couple ultrafast lasers with integrated photonics to create chip-scale devices.

  PublisherOA PDFDOI

• Novel Materials-based Laser Acceleration

  Conference on Lasers and Electro-Optics · 2021-01-01

  article

  We demonstrate the first laser acceleration based on novel dielectric materials (Al 2 O 3 and Ga 2 O 3 ) with high laser damage thresholds, opening a new venue for perfor- mance optimization of dielectric laser accelerators.

  PublisherDOI

• Electron Pulse Compression with Optical Beat Note

  Physical Review Letters · 2021-10-14 · 21 citations

  articleOpen access

  Compressing electron pulses is important in many applications of electron beam systems. In this study, we propose to use optical beat notes to compress electron pulses. The beat frequency is chosen to match the initial electron pulse duration, which enables the compression of electron pulses with a wide range of durations. This functionality extends the optical control of electron beams, which is important in compact electron beam systems such as dielectric laser accelerators. We also find that the dominant frequency of the electron charge density changes continuously along its drift trajectory, which may open up new opportunities in coherent interaction between free electrons and quantum or classical systems.

  PublisherOA PDFDOI

Recent grants

• The Stanford Advanced Gravitational Wave Detector Research Program

  NSF · $950k · 2009–2012

• The Stanford Advanced Gravitational Wave Detector Research Program

  NSF · $2.5M · 2008–2012

• Stanford Program in Support of LIGO

  NSF · $4.2M · 2011–2014

• The Stanford Advanced Gravitational Wave Detector Research Program

  NSF · $4.0M · 2005–2009

• Optical Scale Laser-Driven Electron Accelerators for Attosecond Radiation Sources

  NSF · $450k · 2015–2018

Frequent coauthors

• J. van den Brand

  210 shared

• E. Chassande–Mottin

  Laboratoire AstroParticule et Cosmologie

  163 shared

• J. D. E. Creighton

  159 shared

• B. F. Schutz

  Max Planck Institute for Gravitational Physics

  146 shared

• I. W. Harry

  University of Portsmouth

  145 shared

• B. Willke

  Max Planck Institute for Gravitational Physics

  145 shared

• B. Allen

  145 shared

• R. L. Ward

  University of Glasgow

  137 shared

Education

• Ph.D., Physics

  Stanford University

  1980

• B.S., Physics

  University of California, Berkeley

  1975