In the mid-1950s, Soviet scientists Nikolai Basov and Alexander Prokhorov and their US colleague Charles Townes developed the first sources of coherent radiation, with the academic community immediately realizing their importance for fundamental physics and technology.
Unlike stationary laboratories, first-generation lasers could generate immensely powerful electromagnetic fields. Of course, certain natural phenomena, mostly cosmic processes, generate electromagnetic radiation of comparable and even greater intensity, but it was impossible to use the radiation for laboratory experiments. So physicists saw the first rudimentary and weak laser units as a new and highly promising research tool.
In the 1960s and the 1970s, scientists suggested numerous projects for laser units in fundamental physics. The most famous projects included laser thermonuclear synthesis and the creation of antimatter from vacuum using a powerful laser field. However, these projects required extremely powerful laser beams that seemed unattainable at the time.
Since then, laser technology and equipment continued to develop, with scientists aiming to generate super-powerful laser pulses and improve the quality of laser beams. The specifications of laser units, including cost and size, improved considerably for every watt of generated power. Thus, lasers became less exclusive and turned into relatively inexpensive commercial units.
They proved their value with laser surgery and diagnostics, laser welding and cutting, metrology, laser chemistry and defense projects. These laser units can be used in the most diverse fields.
Lasers can also be found at nearly any physics laboratory.
Locating Natural Resources and Studying Distant Space
Today, lasers are used to measure microscopic distances and time intervals with extreme precision. In 2015, this allowed the LIGO and VIRGO collaborations to “catch” gravitation waves and to accomplish one of the most difficult tasks of fundamental physics for the first time in nearly 100 years. In 2017, the researches of this discovery received the Nobel Prize in physics.
“Laser interferometers are the main components in a LIGO unit, and are used in an extremely complicated experiment: measuring the metrics of space during the passage of a gravitation wave that is triggered by the collision of two black holes,” said Sergei Popruzhenko, a professor at the Department for Theoretical Nuclear Physics at National Research Nuclear University MEPhI. Increasingly more advanced laser technologies will make it possible to develop clocks that will prove to be one microsecond slow during the entire lifespan of the Universe and which would quickly respond to gravitation changes, Acting Director of MEPhI’s Institute of Laser and Plasma Technologies (LAPLAS) Andrei Kuznetsov said.
“What are the practical applications of all this? By learning to measure time with such precision, we will be able to measure changes in the terrestrial gravitation field, and this will make it possible to locate natural deposits. The gravitation field depends on density. Therefore changing ore-density levels will influence the gravitation field, and this will identify the location of heavy ores or oil-bearing layers. Therefore clocks will help us discover various natural resources, including oil, natural gas, heavy metals and rare-earth elements. Also, it will be possible to compile gravitation maps for submarine navigation,” Kuznetsov explained.
Laser clocks serve fundamental research. One theory suggests that fundamental constants, including the Planck constant and an electron’s mass and charge, tend to change in an expanding Universe. Super-stable laser clocks will help prove this theory. Super-long or high-precision time measurements are needed to accomplish this task.
“Earlier this year, MEPhI scientists obtained astonishing results that imply that it is possible to conduct such fundamental experiments. We completed this high level project along with the Russian Academy of Sciences’ Lebedev Physical Institute,” Kuznetsov noted.
Most laser-physics experiments require very powerful and intensive laser beams. Terawatt-class and petawatt-class laser beams are the best tool for the non-explosive compression of substances.
(Editor’s Note: One terawatt equals 1012 watts and one petawatt equals 1015 watt).
“The values are huge, especially given that the world’s largest hydroelectric power station has a rated capacity of 0.05 terawatt. These beams allow researchers to obtain and study various substances in laboratory conditions. These substances have tremendous pressures and temperatures not dissimilar to the inside of a star. It may be a paradox, but laser units with telescopes are becoming the main tool for studying distant space,” Popruzhenko explained.
Heat and Capture Substances
Laser beams can compress substances, heating them up to hundreds of millions of degrees. This can trigger a controlled thermonuclear synthesis reaction.
“Humankind has been trying to harness thermonuclear energy for over 60 years. Recent history has seen thermonuclear explosions, but it is so far impossible to use this energy for peaceful purposes because scientists are unable to capture and use the tremendous energy generated during a thermonuclear reaction,” Kuznetsov said.
Two light nuclei need to merge to obtain one heavy nucleus, and this will trigger thermonuclear synthesis. For this purpose, it is necessary to overcome Coulomb’s barrier when positively charged nuclei are repelled. But this barrier can be eliminated by increasing the kinetic energy of nuclei. This energy needs to be over 100 million degrees Celsius, and such temperatures are only achieved inside stars. This is a major academic and technical hurdle. Physicists are trying to get past this with two methods.
The first method calls for heating up and trapping plasma inside a TOKAMAK (Toroidal Chamber with Magnetic Coils) reactor. Under the second method, a laser unit with energy of over one mega-joule would emit a pulse several nano-seconds long. This energy would penetrate several cubic millimeters of hydrogen-isotope (deuterium/tritium) fuel, compressing and heating it to the temperature needed to launch thermonuclear synthesis. The fuel would burn up completely and generate energy in the form of gamma quantums and alpha particles.
“What are the advantages of thermonuclear reactors over nuclear reactors? Unlike uranium, the world has enough deuterium to last for millions of years. We would have an unlimited amount of energy. On the other hand, thermonuclear energy could be used to develop new engines and launch manned missions to Mars, other parts of the Solar System and beyond. This age-old dream would thus be realized,” Kuznetsov concluded.
When Physical Laws Cease to Function
Like linear particle accelerators, synchrotrons and cyclotrons, lasers can accelerate charged particles. To accomplish this, high-intensity, short and focused laser pulses need to generate more energy.
The advantages of accelerating charged particles by laser beams include an opportunity to simultaneously accelerate electrons and ions. Laser accelerators become smaller and cheaper, making it possible to achieve record-breaking acceleration levels and to influence dense plasmoids.
“Most importantly, it will become possible to create unique conditions by increasing maximum laser-radiation intensity by another 30-40 times. This would help create super-dense electron-positron-photon plasmoids that could have existed during the initial creation of the Universe. In such plasmoids, electromagnetic radiation is linked with substances to such a great extent that ordinary laws of electrodynamics, including those of quantum electrodynamics, no longer apply and become irrelevant. The properties of this object remain unclear, a rare occurrence in truly fundamental physics,” Popruzhenko noted.
Laser units providing such high-intensity radiation will appear in the foreseeable future, that is, 10 to 20 years from now. Such high-intensity laser units will make it possible to create electron-positron-photon plasmoids in a vacuum. Today, scientists are studying the behavior of substances and vacuums under conditions of high-intensity laser radiation.
It will be possible to observe some phenomena linked with the influence of radiation-friction forces, including a new proton-acceleration mechanism, which was predicted by theoretical physicists from MEPhI, in the near future. This requires laser fields with an intensity of 1023-1024 watts per square centimeter. So far, it is not possible to generate such highly intensive laser fields, but they may be achieved using new laser units now being developed in the Czech Republic, France, China and other countries. These units, that will generate 10-20 times more energy, are to start operating within a few years.
MEPhI cooperates proactively with numerous laser laboratories, including the Extreme Light Infrastructure (ELI) Beamlines laser facility near Prague where one of the most powerful lasers ever is now being constructed. Several employees and graduates of MEPhI’s Institute of Laser and Plasma Technologies (LAPLAS) work at ELI Beamlines and are also conducting experiments and other work at MEPhI.