C. McGuinness

Stanford University, Palo Alto, CA, United States

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Publications (20)52.6 Total impact

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    ABSTRACT: The enormous size and cost of current state-of-the-art accelerators based on conventional radio-frequency technology has spawned great interest in the development of new acceleration concepts that are more compact and economical. Micro-fabricated dielectric laser accelerators (DLAs) are an attractive approach, because such dielectric microstructures can support accelerating fields one to two orders of magnitude higher than can radio-frequency cavity-based accelerators. DLAs use commercial lasers as a power source, which are smaller and less expensive than the radio-frequency klystrons that power today's accelerators. In addition, DLAs are fabricated via low-cost, lithographic techniques that can be used for mass production. However, despite several DLA structures being proposed recently, no successful demonstration of acceleration in these structures has so far been shown. Here we report high-gradient (beyond 250 MeV m(-1)) acceleration of electrons in a DLA. Relativistic (60-MeV) electrons are energy-modulated over 563 ± 104 optical periods of a fused silica grating structure, powered by a 800-nm-wavelength mode-locked Ti:sapphire laser. The observed results are in agreement with analytical models and electrodynamic simulations. By comparison, conventional modern linear accelerators operate at gradients of 10-30 MeV m(-1), and the first linear radio-frequency cavity accelerator was ten radio-frequency periods (one metre) long with a gradient of approximately 1.6 MeV m(-1) (ref. 5). Our results set the stage for the development of future multi-staged DLA devices composed of integrated on-chip systems. This would enable compact table-top accelerators on the MeV-GeV (10(6)-10(9) eV) scale for security scanners and medical therapy, university-scale X-ray light sources for biological and materials research, and portable medical imaging devices, and would substantially reduce the size and cost of a future collider on the multi-TeV (10(12) eV) scale.
    Nature 09/2013; 503(7474):91. · 38.60 Impact Factor
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    ABSTRACT: We report the first observation of high-gradient acceleration (>250MeV/m) of electrons in a Dielectric Laser Accelerator (DLA) driven by a mode-locked Ti:sapphire laser.
    Nonlinear Optics; 07/2013
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    ABSTRACT: The quest for less costly and more compact high-energy particle accelerators makes research on alternative acceleration mechanisms an important enterprise. From the multitude of suggested concepts, the photonic accelerator design by B. M. Cowan [Phys. Rev. ST Accel. Beams 11, 011301 (2008)] stands out by its distinct potential of creating an accelerator on a chip [Proposal E-163, SLAC (2001)]. Herein, electrons are accelerated by the axial electric field of a strongly confined optical mode of an air waveguide within a silicon-based three-dimensional photonic band-gap material. Using a combination of direct laser writing and silicon double inversion, we here present the first experimental realization of this complex structure. Optical spectroscopy provides unambiguous evidence for the existence of an accelerating waveguide mode with axial polarization.
    Optics Express 02/2012; 20(5):5607-12. · 3.55 Impact Factor
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    ABSTRACT: A proof of principle fused-silica grating structure has been designed and fabricated for the purpose of direct laser acceleration of electrons. The optimal structure geometry was determined via 2D-FDTD and 3D-FEFD simulations to maximize the available acceleration gradient. The structure was fabricated with standard nanofabrication techniques, including optical lithography, reactive ion etching, and wafer bonding. Beam tests have been performed with the 60MeV beam at the Next Linear Collider Test Accelerator at SLAC, with successful demonstration of electron transmission through the micron-scale apertures.
    Proceedings of the 2012 Advanced Accelerator Concepts Workshop; 01/2012
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    ABSTRACT: Photonic crystal waveguides are promising candidates for laser-driven accelerator structures because of their ability to confine a speed-of-light mode in an all-dielectric structure. Because of the difference between the group velocity of the waveguide mode and the particle bunch velocity, fields must be coupled into the accelerating waveguide at frequent intervals. Therefore efficient, compact couplers are critical to overall accelerator efficiency. We present designs and simulations of high-efficiency coupling to the accelerating mode in a three-dimensional photonic crystal waveguide from a waveguide adjoining it at 90{sup o}. We discuss details of the computation and the resulting transmission. We include some background on the accelerator structure and photonic crystal-based optical acceleration in general.
    01/2012;
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    ABSTRACT: In this article we demonstrate the net acceleration of relativistic electrons using a direct, in-vacuum interaction with a laser. In the experiment, an electron beam from a conventional accelerator is first energy modulated at optical frequencies in an inverse-free-electron-laser and bunched in a chicane. This is followed by a second stage optical accelerator to obtain net acceleration. The optical phase between accelerator stages is monitored and controlled in order to scan the accelerating phase and observe net acceleration and deceleration. Phase jitter measurements indicate control of the phase to $13 allowing for stable net acceleration of electrons with lasers.
    Physical Review Special Topics - Accelerators and Beams 11/2011; 11(10). · 1.57 Impact Factor
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    ABSTRACT: We present our progress in the fabrication and measurement of a transmission-based dielectric double-grating acceleration structure. The structure lends itself to simpler coupling to the accelerating mode in the waveguide with negligible group velocity dispersion effects, allowing for operation with ultra-short (fs) laser pulses. This document describes work being done at the Stanford Nanofabrication Facility to create a monolithic guided-wave structure with 800 nm period gratings separated by a fixed subwavelength gap using standard optical lithographic techniques on a fused silica substrate. An SEM and other characterization tools were used to measure the fabrication deviations of the grating geometry and simulations were carried out in MATLAB and HFSS to study the effects of such deviations on the resulting accelerating gradient.
    2011 Particle Accelerator Conference; 01/2011
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    ABSTRACT: Eight and nine layer three dimensional photonic crystals with a defect designed specifically for accelerator applications have been fabricated. The structures were fabricated using a combination of nanofabrication techniques, including low pressure chemical vapor deposition, optical lithography, and chemical mechanical polishing. Limits imposed by the optical lithography set the minimum feature size to 400 nm, corresponding to a structure with a bandgap centered at 4.26 mum. Reflection spectroscopy reveal a peak in reflectivity about the predicted region, and good agreement with simulation is shown. The eight and nine layer structures will be aligned and bonded together to form the complete seventeen layer woodpile accelerator structure.
    11/2010;
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    ABSTRACT: An overmoded photonic crystal waveguide based on the three-dimensional woodpile lattice has been proposed for a highenergy charged particle accelerator. Critical to overall accelerator efficiency is the ability to couple power into an uninterrupted vacuum waveguide in a very small volume. We present designs and simulations of coupling to the waveguide, both from free space and from a waveguide adjoining it at 90 degrees. We discuss details of the computation, including the use of symmetries and extraction of the resulting transmission.
    Proc SPIE 02/2010;
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    C. McGuinness, E. Colby, R. L. Byer
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    ABSTRACT: We present work done towards the successful fabrication of a four-layer woodpile photonic crystal with a bandgap of 0.876mm centered at 4.55mm. The goal of this fabrication was to develop a process flow that will be used to fabricate a 15-layer woodpile structure with a defect used for accelerating electrons. The structure dimensions were designed using simulations to maximize the bandgap, and scaled by the minimum features achievable in the optical lithography process. Infrared spectroscopy measurements were taken of the resulting four-layer structure, demonstrating a clear bandgap region centered at 4.55mm, with a full-width at half maximum (FWHM) of 2.72mm. Variations in the actual fabricated structure were measured via SEM images, and the deviations were incorporated into simulations. The center bandgap wavelength predicted in simulations agrees to within 1% of the measured value, and the FWHM agrees to within 15% of the measurement. These results provide validation for the quality of the photonic crystal fabricated.
    Journal of Modern Optics 10/2009; 56(18):2142-2147. · 1.16 Impact Factor
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    ABSTRACT: The goals of this paper is: (1) to produce optically spaced electron microbunches; (2) to obtain independent verification and measure of microbunching; and (3) perform net acceleration of electrons with a laser.
    06/2009
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    ABSTRACT: An experimental effort is currently underway at the E-163 test beamline at Stanford Linear Accelerator Center to use a hollow-core photonic bandgap (PBG) fiber as a high-gradient laser-based accelerating structure for electron bunches. For the initial stage of this experiment, a 50pC, 60 MeV electron beam will be coupled into the fiber core and the excited modes will be detected using a spectrograph to resolve their frequency signatures in the wakefield radiation generated by the beam. They will describe the experimental plan and recent simulation studies of candidate fibers.
    01/2009;
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    ABSTRACT: We describe initial steps at fabricating a dielectric photonic bandgap accelerator structure designed to operate at near IR frequencies. Such a structure operating at these frequencies requires extremely small, sub-micron sized features, forcing one to use lithographic means for fabrication. A process based upon lithographic equipment at the Stanford Nanofabrication Facility has been developed and a four layer test structure has been fabricated. Unexpected problems with the final etch step, and corresponding modifications to the process flow addressing these problems, are described. Spectroscopic measurements of the structure have been taken and are compared to simulations.
    01/2009;
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    ABSTRACT: We report the production of optically spaced attosecond electron microbunches produced by the inverse free-electron-laser (IFEL) process. The IFEL is driven by a Ti:sapphire laser synchronized with the electron beam. The IFEL is followed by a magnetic chicane that converts the energy modulation into the longitudinal microbunch structure. The microbunch train is characterized by observing coherent optical transition radiation (COTR) at multiple harmonics of the bunching. Experimental results are compared with 1D analytic theory showing good agreement. Estimates of the bunching factors are given and correspond to a microbunch length of 410 attosec FWHM. The formation of stable attosecond electron pulse trains marks an important step towards direct laser acceleration.
    Physical Review Letters 06/2008; · 7.73 Impact Factor
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    ABSTRACT: We present a series of laser-driven particle acceleration experiments that are aimed at studying laser-particle acceleration as an inverse-radiation process. To this end we employ a semi-open vacuum setup with a thin planar boundary that interacts with the laser and the electromagnetic field of the electron beam. Particle acceleration from different types of boundaries will be studied and compared to the theoretical expectations from the Inverse-radiation picture and the field path integral method. We plan to measure the particle acceleration effect from transparent, reflective, black, and rough surface boundaries. While the agreement between the two acceleration pictures is straightforward to prove analytically for the transparent and reflective boundaries the equivalence is not clear-cut for the absorbing and rough-surface boundaries. Experimental observation may provide the evidence to distinguish between the models.
    01/2008
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    ABSTRACT: The laser acceleration experiments conducted for the El63 project at the NLC Test Accelerator facility at SLAC have stringent requirements on the temporal properties of the electron and laser beams. A system has been implemented to measure the relative phase stability between the RF sent to the gun, the RF sent to the accelerator, and the laser used to generate the electrons. This system shows rms timing stability better than 1 psec. Temporal synchronicity between the 0.5 psec electron bunch, and the 0.5 psec laser pulse is also of great importance. Cherenkov radiation is used to measure the arrival time of the electron bunch with respect to the laser pulse, and the path length of the laser transport is adjusted to optimize temporal overlap. A linear stage mounted onto a voice coil is used to make shot- by-shot fine timing adjustments to the laser path. The final verification of the desired time stability and control is demonstrated by observing the peak of the laser-electron interaction signal over the course of several minutes.
    Particle Accelerator Conference, 2007. PAC. IEEE; 07/2007
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    W. Zacherl, E. Colby, T. Plettner, C. McGuinness
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    ABSTRACT: The E163 laser acceleration experiments conducted at SLAC have stringent requirements on the temporal properties of two regeneratively amplified, 800 nm,Spitfire laser systems. To determine the magnitude and cause of timing instabilities between the two Ti:sapphire amplifiers, we pass the two beams through a cross-correlator and focus the combined beam onto a Hamamatsu G1117 photodiode. The photodiode has a bandgap such that single photon processes are suppressed and only the second order, two-photon process produces an observable response. The response is proportional to the square of the intensity. The diode is also useful as a diagnostic to determine the optimal configuration of the compression cavity.
    Particle Accelerator Conference, 2007. PAC. IEEE; 07/2007
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    ABSTRACT: The NLC test accelerator (NLCTA) was built to address beam dynamics issues for the Next Linear Collider and beyond. An S-Band RF gun, diagnostics and low energy spectrometer (LES) at 6 MeV together with a large-angle extraction line at 60 MeV have now been built and commissioned for the laser acceleration experiment,E163. Following a four quad matching section after the NLCTA chicane, the extraction section is followed by another matching section, final focus and buncher. The laser-electron interaction point (IP) is followed by a broad range, high resolving power spectrometer (HES) for electron bunch analysis. Optical symmetries in the design of the 25.5deg extraction line provide 1:1 phase space transfer without sextupoles for a large, 6D phase space volume and range of input conditions. Spot sizes down to a few microns at the IP (HES object) allow testing microscale structures with high resolving power at the HES image. Tolerances, tuning sensitivities, diagnostics and the latest commissioning results are discussed and compared to design expectations.
    Particle Accelerator Conference, 2007. PAC. IEEE; 07/2007
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    ABSTRACT: We present an overview of the future laser-driven particle acceleration experiments. These will be carried out at the E163 facility at SLAC. Our objectives include a reconfirmation of the proof-of-principle experiment, a staged buncher laser-accelerator experiment, and longer-term future experiments that employ dielectric laser-accelerator microstructures.
    AIP Conf. Proc. 01/2006; 877:103-116.
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    Ziran Wu, C. Ng, C. McGuinness, E. Colby
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    ABSTRACT: Three-dimensional woodpile photonic bandgap (PBG) waveguide enables high-gradient and efficient laser driven acceleration, while various accelerator components, including laser couplers, power transmission lines, woodpile accelerating and focusing waveguides, and energy recycling resonators, can be potentially integrated on a single monolithic structure via lithographic fabrications. This paper will present designs of this on-chip accelerator based on silicon-on-insulator (SOI) waveguide. Laser power is coupled from free-space or fiber into SOI waveguide by grating structures on the silicon surface, split into multiple channels to excite individual accelerator cells, and eventually gets merged into the power recycle pathway. Design and simulation results will be presented regarding various coupling components involved in this network.