The Race for Ultrapowerful Lasers: A Quantum Leap Ahead
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Chapter 1: The Global Competition for Laser Power
Countries today are engaged in a fierce rivalry to develop the most potent laser systems. In 2015, Japan set a record with a laser output of 2 Petawatts (PW), equivalent to 2 million billion watts. The following year, China surpassed this milestone, achieving 5.3 PW. Then, in March 2019, Romania's Extreme Light Infrastructure for Nuclear Physics (ELI-NP) project reached an impressive 10 PW.
For context, the most powerful commercial laser available, the Spyder 3 Arctic, operates at just about 3.5 watts, while standard laser pointers are measured in milliwatts. Although it is possible to construct more powerful lasers, as showcased in a remarkable 100-watt laser demonstration by YouTuber styropyro, it is crucial to note that such lasers can pose serious safety risks. They have the potential to cause blindness, burns, or cuts, and their intense heat generation can create considerable fire hazards without adequate cooling measures.
Petawatt lasers, while incredibly powerful, do not consume as much energy as one might expect. A watt represents energy over time, and these lasers typically release brief bursts of high-intensity light lasting only a trillionth of a second. The first petawatt laser was developed at the Lawrence Livermore National Laboratory, home to the National Ignition Facility, where I once contemplated a job (which I turned down with a tinge of regret to pursue studies at Georgia Tech).
The advancement of ultrapowerful lasers has followed a trajectory reminiscent of Moore's Law in computing over the past 40 years. Since their inception in the 1960s at HRL Laboratories, lasers have found remarkable applications in both industrial and military sectors. However, the potential of these lasers extends even further, as they may serve as a pathway to achieving the long-sought goal of nuclear fusion.
There are ambitious projects underway in Russia, China, and beyond to construct lasers exceeding 100 PW, where the science becomes especially intriguing. For instance, this could lead to the creation of antimatter from a vacuum.
Some literature suggests that lasers can tear apart empty space, but this is a misinterpretation. In reality, the energy generated is so concentrated that it significantly increases the likelihood of matter being produced from electric fields or through the splitting of photons into particles.
A brief note for physics enthusiasts: The phenomenon of antimatter generation from a vacuum and an electric field is known as the Sauter-Schwinger effect. Additionally, photons can create matter-antimatter pairs through a process called Breit-Wheeler pair production or electron-positron photoproduction.
Section 1.1: Intensity: The Key Metric for Lasers
The intensity of a laser, measured in watts per square centimeter, is crucial for applications like fusion or other noteworthy physical phenomena. The anticipated 100 PW laser in Shanghai aims to reach an intensity of approximately 10^23 watts per square centimeter in 15 femtosecond bursts—about the time it takes light to traverse half the length of a human blood cell.
At these extreme intensity levels, we might witness light interacting with itself in previously unobserved ways. Ordinarily, light does not interact with other light; it interacts with matter instead. This could result in light appearing to bend through a vacuum.
However, the intensity required to observe such effects is roughly one million times greater than what the Shanghai laser can provide (requiring a Zettawatt laser). Fortunately, we have a method to observe these interactions utilizing relativity.
Subsection 1.1.1: Harnessing Relativity for Enhanced Observations
The critical intensity necessary to observe light-light interactions is around 4.6 x 10^29. The intensity of a laser can change based on your relative motion (velocity) to it, as outlined by Einstein’s theory of special relativity.
To observe these effects, one could direct a beam of electrons at near-light speed towards the laser. Due to relativistic effects, the apparent intensity in the electrons' frame of reference can be increased by a factor of one million when traveling at 99.99995% the speed of light. This can be accomplished through a process called laser-wakefield or plasma acceleration.
Currently, the record for electron acceleration is held by Lawrence Berkeley National Laboratory, which has achieved 4.25 GeV electrons—enough to reach 99.999999277% of the speed of light.
Another method involves Compton backscattering, where electrons amplify photons of light. This technique can also enhance intensity through relativistic effects, with the current record set by the Laser Electron Photon (LEP) experiment in Japan at 2.9 GeV.
Section 1.2: The Nonlinear World of Quantum Electrodynamics
At these intense levels, light exhibits nonlinear behavior due to Quantum Electrodynamics (QED). In nonlinear QED, the fundamental equations governing electrodynamics are modified, allowing electric and magnetic fields to interact with one another. This could lead to light bending in a vacuum as it scatters off virtual electron-positron pairs. Exploring nonlinear QED might reveal deeper insights into quantum field theory beyond what particle accelerators can achieve.
Chapter 2: The United States and the Global Race for Laser Technology
How Does a Laser Work? Quantum Nature of Light - YouTube
In the context of this global competition, it is unfortunate to note that the United States appears to be lagging behind. Countries like China, Russia, Japan, and those in Europe have taken the lead, despite the U.S. having initiated its efforts two decades earlier. The U.S. has primarily invested in lower-power, high-energy lasers, such as the National Ignition Facility, which aims to study nuclear fusion and replicate atomic testing conditions without the use of nuclear weapons.
The most powerful laser project in the U.S. is currently the ZEUS initiative at the University of Michigan, which seeks to achieve 3 PW. Given the potential economic and scientific benefits of these lasers in generating new energy sources, medical applications, and advancing our understanding of quantum physics, the $16 million budget for ZEUS seems modest compared to the nearly $1 billion allocated by the EU for their 10 PW project. A 2018 report from the National Academies of Sciences highlighted the need for the U.S. to update its strategic planning for ultra-high power lasers to remain competitive.
Ultimately, there is a need for balance when it comes to funding research in the U.S. In the realm of big science, the U.S. has often opted to remain on the sidelines, allowing other nations to take the lead. (I recall the disillusionment following the cancellation of the Texas supercollider project.) Science is inherently a borderless pursuit; why invest heavily when other countries can undertake the work and share the benefits? However, these facilities often operate under priorities that differ from our own. A stronger collaboration between American industry and science could yield significant advancements if more resources were allocated to these laser technologies and similar large-scale efforts. After all, Americans generally do not enjoy losing in any endeavor, do we?
Quantum limits of field sensing with ordinary and ultracold matter - Morgan Mitchell (ICFO)