CREATING A SUPER POWER LASER
PEARL is a femtosecond laser complex, one laser pulse of which is hundreds of times greater than the power of all power plants on Earth. With the help of this laser, it is possible to study processes in supercritical conditions (similar to those in the Solar core). The new laser system will certainly find its application in medicine, biology, physics, and materials science. The new laser will also help astrophysicists in studying various phenomena. For example, it will let people understand the processes in pulsars, brown dwarfs and exoplanets. Scientists hope that the new laser will allow them to reveal many secrets of the Universe.
The femtosecond laser complex PEARL was created at the Institute of Applied Physics of the Russian Academy of Sciences (IAP RAS) in Nizhny Novgorod, in 2006. The city physicists have found for the complex a very suitable abbreviation PEARL, which means in Russian “zhemchuzhina”. The full name of the complex is – PEtawatt pARametric Laser. At the moment, PEARL is among the five most powerful lasers in the world, and it will not be easy to maintain such a high status due to the extremely high activity of the world’s leading powers in creating super power lasers.
The principles of radiation generation at the PEARL laser complex are different from the traditional ones. Usually, laser radiation is produced in special lasing media. First it is “pumped up” with energy, exciting atoms, and then a low-power pulse passes through it. Passing through the media, the pulse induces radiation of excited atoms, which adds up to the initial pulse and amplifies it. The fundamental problem is the phenomenon of spontaneous emission – excited atoms emit even in the absence of an external pulse, and therefore the lasing media begins to “shine” even before its arrival, creating a prepulse.
At the PEARL complex, a different principle is used to produce super power pulses – parametric amplification. In this principle, the amplification of a short pulse occurs in a nonlinear optical crystal as a result of direct interaction with the “pumping” laser pulse. The “pumping” pulse in this case is much longer than the amplified pulse, and therefore has a low power. The amplified pulse “runs” through it and collects energy, gaining much higher power. In this principle, there is no spontaneous radiation, and the prepulse is much weaker.
The interest of nuclear scientists in super power lasers can be explained by the attractive prospects of laser fusion, the main alternative to the Tokamak-type reactor. Recall that in a tokamak the deuterium-tritium plasma is supposed to be held for a relatively long period of time (about one second). At the same time, laser thermonuclear fusion assumes significantly shorter time intervals (about 10-10 seconds) at substantially higher deuterium and tritium concentrations.
The PEARL complex architecture is based on the original OPCPA scheme that allows obtaining a total energy gain over 1010 in three crystals only. The IAP RAS researchers were the first to formulate, develop and test in experiments the OPCPA concept. This scheme is now recognized worldwide as the most promising or mastering new frontiers of laser radiation power and intensity.
For the first time, pulses with a duration of less than 15 femtoseconds (1 fs = 10-15 seconds) were produced at the Facility with more than 1 petawatt power (1 PW = 1015 watts). Record parameters of the pulse (a duration of 11 fs and a power of 1.5 PW) were obtained on the PEARL laser complex of the Institute of Applied Physics of the Russian Academy of Sciences. This became possible thanks to the unique approach of additional compression, shortening the duration of the pulse, – CafCA (Compression after Compressor Approach). The optical pulse becomes several times shorter than the original one, and its peak power increases by the same number of times, since the pulse energy almost does not change during the conversion. The approach is based on the broadening of the optical radiation spectrum as it passes through a nonlinear element. The spectral phase dependence of the radiation, introduced by the nonlinear element, is compensated by the reflection from a special mirror, resulting in a shorter pulse. Record parameters of the pulse compression factor were obtained – more than 6. When creating the optical circuit the effect of self-filtration of small-scale fluctuations of high-intensity optical radiation, discovered by the authors earlier, was used.
One should expect widespread of laser systems of this type in all areas from medicine to nuclear technology. These systems are sources of powerful radiation of various ranges and high-energy particles with unique characteristics. For example, there is a project to create a super bright source spot of the X-ray for the Phase-contrast X-ray imaging, which has great prospects in medicine. Powerful sources of terahertz radiation will almost certainly find a niche.