Optimizing the phase focusing of laser accelerators

With the help of on-chip accelerator technology, researchers at Stanford University are getting closer to manufacturing a miniature electron accelerator that can have various applications in industrial, medical, and physical research.

Scientists have proven that silicon dielectric laser accelerators can now be used to accelerate and limit electrons, thereby producing concentrated high-energy electron beams. The study was published in the journal Physical Review Letters.

The high-energy particle beams generated by accelerators enable physicists to study material properties, create targeted probes for medical applications, and determine the fundamental components of the matter that make up the universe. Some of the earliest high-energy particle accelerators were developed in the 1930s and were small enough to be placed on a desktop.

However, higher particle energy is needed to study more complex physics, which means scientists must build larger systems. The original linear accelerator tunnel of the SLAC National Accelerator Laboratory on Stanford University campus was put into use in 1966 and is nearly 2 miles long.

Professor Olav Solgaard, senior author of the paper, Edward L. Ginzton Laboratory Director, and Professor Robert L. and Audrey S. Hancock from the School of Engineering, stated that this vision is becoming increasingly feasible due to advancements in nanoscale manufacturing and laser technology. Traditional RF accelerators consist of radio waves pumped into copper cavities, increasing the energy of particles.
Due to the possibility of metal being heated by these pulses, the cavity must operate at a lower energy and pulse rate to dissipate heat and prevent melting.

However, glass and silicon structures can be stronger and smaller because they can withstand higher energy laser pulses without overheating. About ten years ago, researchers at Stanford University began conducting experiments on the nanoscale structures of these materials. In 2013, a group led by Robert Bayer, Honorary Professor William R. Kennan, and co authors of the paper demonstrated that electrons can be successfully accelerated through tiny glass accelerators using pulsed infrared light.

Due to these achievements, the Gordon and Betty Moore Foundation accepted the project as part of a global collaboration on chip accelerators, aimed at creating a shoe box sized giant electron volt accelerator.

However, the initial "chip accelerator" still had issues. According to Broaddus, the electrons inside are like cars on narrow roads without steering wheels - they can easily hit walls and accelerate extremely quickly.

The research team at Stanford University has now successfully demonstrated their ability to control electrons at the nanoscale. To achieve this goal, they created a silicon structure with submicron channels in a vacuum system. They put electrons into one end and use a shaped laser pulse that generates kinetic energy to illuminate the structure from both sides. By periodically flipping between the focusing and defocusing characteristics of the laser field, electrons are prevented from deviating from their orbits.

Electrons are affected by this sequence of acceleration, defocusing, and focusing, exceeding nearly one millimeter. Although it may not seem much, the energy of these charged particles significantly increases, by 23.7 kiloelectron volts, or about 25%, compared to their initial energy. The acceleration speed of the team's prototype micro accelerator is comparable to that of traditional copper accelerators, and Broaddus stated that it can achieve higher acceleration speeds.

Although this is a big step in the right direction, more work is needed before applying these micro accelerators to business, healthcare, and research. The team can only manipulate electrons in two-dimensional space; Three dimensional electron constraints are needed to extend the accelerator for a sufficient amount of time to achieve higher energy gain.

Broaddus mentioned that a sister research group at Friedrich Alexander University in Erlangen, Germany recently demonstrated a similar device that uses a single laser and starts at significantly lower initial energy levels. He stated that FAU devices and Stanford devices will ultimately form part of the electronic relay competition he described.

Three people will participate in the upcoming relay race. After receiving the initial booster from the FAU device, low-energy electrons can be fed into devices similar to those being created by Broaddus. For electrons, the final step will be an accelerator made of glass, similar to the accelerator created by Bayer. Due to glass being more resistant to laser radiation than silicon, accelerators can excite more electrons and accelerate them to the speed of light.

Solgard believes that ultimately, like larger accelerators, these tiny accelerators will contribute to high-energy physics and explore the fundamental substances that make up the universe. Although "we still have a long way to go," Solgard remained optimistic and added, "we have taken the first few steps.".

Source: Laser Net