The American team precisely controls the ultra fast laser, which accelerates the

Recently, a research cooperation team in the United States announced that they could accelerate the electron within 20 cm to the speed that is usually reached only by particle accelerators with the size of 10 football fields through the precise control of ultrafast lasers.

It is reported that a team led by Howard Milchberg, a professor of physics, electronics and computer engineering at the University of Maryland (UMD), cooperated with Jorge J. Rocca's team at Colorado State University (CSU) to achieve this feat by using two laser pulses generated by hydrogen injection.

Simulation diagram: the laser pulse (red) drives the plasma wave to accelerate the electrons in its wake. The bright yellow dot is the area with the highest electron concentration. In one experiment, scientists used this technique to accelerate electrons to nearly the speed of light in a span of 20 centimeters. (Image source: UMD)

In this process, the first pulse tears the hydrogen, making a hole in the hydrogen and forming a plasma channel. This channel guides a second higher power pulse to absorb electrons from the plasma and drag them in its wake, accelerating the electrons to near the speed of light in this process. Through this technology, the team accelerated electrons to nearly 40% of the energy obtained in large facilities (SLAC National Accelerator Laboratory coherent light source LCLS).

LCLS is a "tunnel" with a length of 1km, which can generate the world's most powerful X-ray laser beam with its ultrafast electrons. At present, it can also accelerate electrons to 13.6 billion electron volts (GeV), which is the energy when electrons move at 99.999999993% of the speed of light.

Milchberg, a researcher at the Institute of Electronics and Applied Physics at the University of Michigan, said that this is the first multi GeV electron accelerator driven entirely by lasers. With the lower cost and higher efficiency of lasers, it is expected that this technology will become a major extension of researchers in this field. The above papers will be published in Physical Review X on August 1, 2022.

Accelerating electrons to the energy of billions of electron volts (GeV) is not easy. In order to expand the scale of this technology to a more controllable extent, the UMD and CSU teams strive to use light itself to increase the speed of electrons to close to the speed of light.

The ultimate goal of the researchers is to reduce the GeV scale electron accelerator to a medium-sized room. Creating these stronger acceleration fields in the laboratory requires a process called laser wakefield acceleration. In this process, a tightly focused intense laser pulse generates disturbance through the plasma and pulls electrons in its wake.

It is a technology pioneered by the UMD team that enables the above cooperative teams to use wake field acceleration more effectively than ever before. This technology can suppress high-energy beams and prevent their energy from being excessively dispersed. Their technology makes a hole in the plasma to form a waveguide to focus the energy of the beam.

Their technology has created something similar to fiber optic cable - something that can transmit optical Internet services and other telecommunications signals in thin air. Or, more accurately, it is made by carefully controlled hydrogen injection.

The traditional optical fiber waveguide consists of two parts: a central "core" to guide light and a surrounding "cladding" to prevent light leakage. In order to manufacture the plasma waveguide, the cooperative research team used additional laser beams and hydrogen jets. When this extra "guiding" laser passes through the jet, it strips electrons from the hydrogen atoms and forms a plasma channel. At this time, the plasma is hot and starts to expand rapidly to form a plasma "core" with lower density, while a gas with higher density is formed at its edge, just like a cylindrical shell. The main laser beam (the laser beam that will collect electrons in its wake) is then sent through this channel. The front end of the pulse also transforms the high-density shell into plasma, forming "cladding".

The results show that the researchers can accelerate some electrons to an amazing 5 GeV by using the optical plasma waveguide technology of the University of Maryland (UMD), combined with the high-energy lasers and professional knowledge of the Colorado State University team. This is still 3 times lower than the large accelerator of SLAC, and has not reached the maximum value of laser wake field acceleration. However, in this new study, the laser energy used per GeV acceleration set a new record, and the team said that their technology was more versatile: it could generate thousands of electron bursts per second (rather than about once per second), making it a promising technology for many applications.

Source: OFweek Laser Network