K. Soong

Demonstration of electron acceleration in a laser-driven dielectric microstructure

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 having been proposed recently, no successful demonstration of acceleration in these structures has so far been shown. Here we report high-gradient (beyond 250u2009MeVu2009m−1) acceleration of electrons in a DLA. Relativistic (60-MeV) electrons are energy-modulated over 563u2009±u2009104 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 10–30u2009MeVu2009m−1, and the first linear radio-frequency cavity accelerator was ten radio-frequency periods (one metre) long with a gradient of approximately 1.6u2009MeVu2009m−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 (106–109u2009eV) 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 (1012u2009eV) scale.

Dielectric laser accelerators

We describe recent advances in the study of particle acceleration using dielectric near-field structures driven by infrared lasers, which we refer to as Dielectric Laser Accelerators. Implications for high energy physics and other applications are discussed.

Demonstration of acceleration of relativistic electrons at a dielectric microstructure using femtosecond laser pulses

Acceleration of electrons using laser-driven dielectric microstructures is a promising technology for the miniaturization of particle accelerators. Achieving the desired GV m-1 accelerating gradients is possible only with laser pulse durations shorter than ∼1u2009u2009ps. In this Letter, we present, to the best of our knowledge, the first demonstration of acceleration of relativistic electrons at a dielectric microstructure driven by femtosecond duration laser pulses. Using this technique, an electron accelerating gradient of 690±100u2009u2009MVu2009m-1 was measured-a record for dielectric laser accelerators.

Laser damage threshold measurements of optical materials for direct laser accelerators

The laser-damage threshold is a fundamental limit for any dielectric laser-driven accelerator and is set by the material of the structure. In this paper, we present a theoretical model of the laser damage mechanism, in comparison with experimental data on the damage threshold of silicon. Additionally, we present damage threshold measurement data of various optical materials, most of which have not been previously characterized in the picosecond-regime.

Design of a subnanometer resolution beam position monitor for dielectric laser accelerators

We present a new concept for a beam position monitor with the unique ability to map particle beam position to a measurable wavelength. Coupled with an optical spectrograph, this beam position monitor is capable of subnanometer resolution. We describe one possible design, and through finite-element frequency-domain simulations, we show a resolution of 0.7 nm. Because of its high precision and ultracompact form factor, this device is ideal for future x-ray sources and laser-driven particle accelerators on a chip.

Electron beam position monitor for a dielectric microaccelerator

We report the fabrication and first demonstration of an electron beam position monitor for a dielectric microaccelerator. This device is fabricated on a fused silica substrate using standard optical lithography techniques and uses the radiated optical wavelength to measure the electron beam position with a resolution of 10 μm, or 7% of the electron beam spot size. This device also measures the electron beam spot size in one dimension.

Grating-based deflecting, focusing, and diagnostic dielectric laser accelerator structures

Recent technological advances has made possible the realization of the first laser-driven particle accelerator structure to be fabricated lithographically. However, a complete particle accelerator requires more than just accelerating elements. In this paper, we present a grating-based design for three other quintessential accelerator elements: the focusing structure, the deflecting structure, and the diagnostic structure.

Design, fabrication, and testing of a fused-silica dual-layer grating structure for direct laser acceleration of electrons

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.

Experimental results from the micro-accelerator platform, a resonant slab-symmetric dielectric laser accelerator

We describe experimental measurements of energy modulation obtained using the Micro Accelerator Platform (MAP), a slab-symmetric dielectric laser accelerator based on a resonant structure, at the SLAC E-163 beamline. The structure is powered by a Ti:Sapphire laser side-coupled into a vacuum gap, where the MAP’s periodicity and dimensions create a synchronous accelerating mode. The accelerating field experienced by the electron beam is greater than that in the incoming laser radiation by an enhancement factor on the order of 3 to 5, due to the resonant buildup of the cavity fields. Results presented here demonstrate acceleration in a resonant dielectric structure for the first time. Measured acceleration gradients are on the order of tens of MeV/m when the structure is illuminated with laser power well below breakdown limits. Careful comparison between simulation and experiment suggests that results depend sensitively on the degree of uniformity achieved in fabrication. Acceleration gradients of up to 1 Ge...

Beam dynamics and wakefield simulations of the double grating accelerating structure

Laser-driven acceleration in dielectric structures can provide gradients on the order of GeV/m. The small transverse dimension and tiny feature sizes introduce challenges in design, fabrication, and simulation studies of these structures. In this paper we present the results of beam dynamic simulation and short range longitudinal wakefield simulation of the double grating structure. We show the linear trend of acceleration in a dielectric accelerator design and calculate the maximum achievable gradient equal to 0.47E0 where E0 is maximum electric field of the laser excitation. On the other hand, using wakefield simulations, we show that the loss factor of the structure with 400nm gap size will be 0.12GV/m for a 10fC, 100as electron bunch which is an order of magnitude less than expected gradient near damage threshold of the device.