Two physicists at RIKEN have realized extremely short laser pulses with a peak power of 6 terawatts (6 trillion watts) - roughly equivalent to the power generated by 6,000 nuclear power plants. The achievement, which will contribute to the further development of attosecond lasers, has earned the three researchers the 2023 Nobel Prize in Physics. The study was published in the journal Nature Photonics.
Just as a camera flash can "freeze" fast-moving objects to make them appear as if they are standing still in a photograph, very short laser pulses can help illuminate ultrafast processes, giving scientists a powerful way to image and detect them.
For example, laser pulses on the order of attoseconds (1 attosecond = 10-18 seconds) are so short that they can reveal the motion of electrons in atoms and molecules, providing a new way to discover the evolution of chemical and biochemical reactions. Even light appears to be able to crawl on such short time scales, taking about 3 arsec to pass through a nanometer.
"By capturing the motion of electrons, attosecond lasers make a significant contribution to basic science," said Eiji Takahashi of RIKEN's Center for Advanced Photonics (RAP), "and they are expected to have applications in a wide range of fields, including the observation of biological cells, the development of new materials and the diagnosis of medical conditions."
More impactful
However, while it is possible to create ultrashort laser pulses, they lack impact and have low energy. Creating ultrashort, high-energy laser pulses would greatly expand their possible uses, says Eiji Takahashi: "The current output energy of attosecond lasers is extremely low. Therefore, increasing their output energy is crucial if they are to be used as light sources in a wide range of fields."
Just as audio amplifiers are used to enhance sound signals, laser physicists use optical amplifiers to increase the energy of laser pulses. These amplifiers typically use nonlinear crystals that respond specifically to light. However, if these crystals are used to amplify single-cycle laser pulses, they can be irreparably damaged. Single-cycle laser pulses are so short that the pulse ends before the light has oscillated through a full wavelength cycle.
The biggest bottleneck in the development of high-energy, ultrafast infrared laser sources is the lack of an effective method to directly amplify single-cycle laser pulses," said Eiji Takahashi. This bottleneck results in a 1-millijoule barrier for single-cycle laser pulse energy."
Setting a new record
However, this bottleneck has now been broken. They have amplified single-cycle pulses to more than 50 millijoules, more than 50 times the previous best result. Because the resulting laser pulses are so short, this energy translates into incredibly high power of a few terawatts.
Takahashi said, "We have demonstrated how to overcome the bottleneck by establishing an efficient method to amplify single-cycle laser pulses."
Their method, called advanced doubly chirped optical parametric amplification (DC-OPA), is very simple and involves only two crystals that amplify complementary regions of the spectrum.
Takahashi said, "Advanced DC-OPA for amplifying single-cycle laser pulses is so simple that it's just based on the combination of two nonlinear crystals - it feels like an idea anyone could come up with. It amazes me that such a simple concept provides a new amplification technique and a breakthrough in the development of high-energy ultrafast lasers."
Importantly, the advanced DC-OPA operates over a very wide range of wavelengths. The team was able to amplify pulses with a wavelength difference of more than twice the wavelength.Takahashi said, "This new method has the revolutionary feature that the amplification bandwidth allows for ultra-wide frequency output without affecting the output energy scaling characteristics."
Novel amplification technique
Their technique is a variant of another optical pulse amplification technique called "chirped-pulse amplification," for which three researchers from the U.S., France, and Canada were awarded the Nobel Prize in Physics in 2018. lasers is one of the technologies driving the development of lasers.
Takahashi expects that their technology will further advance the development of attosecond lasers: 'We have successfully developed a new laser amplification method that can increase the intensity of single-cycle laser pulses to terawatt peak power,' he said, 'and there is no doubt that this is the a major leap forward in the development of high-power attosecond lasers."
In the long run, his goal is to go beyond the attosecond laser and create even shorter pulses.
