Short, powerful laser pulses make attosecond imaging possible

Two RIKEN physicists have achieved extremely short laser pulses with a peak power of 6 terawatts (6 megawatts), roughly equivalent to the power produced by 6,000 nuclear power plants. This achievement will help further develop attosecond lasers, and three researchers won the 2023 Nobel Prize in Physics. Nature Photonics.

Just like a camera flash can “freeze” fast-moving objects so that they appear stationary in a photo, extremely short laser pulses can help illuminate ultrafast processes, giving scientists a powerful way to image and Detect them.

For example, a laser pulse on the order of attoseconds (1 attosecond = 10¹⁸ The second) are so short that they can reveal the movement of electrons in atoms and molecules, providing a new way to discover how chemical and biochemical reactions evolve. Even light can crawl on such short time scales, taking about 3 attoseconds to travel through a nanometer.

“By capturing the motion of electrons, attosecond lasers make a significant contribution to basic science,” said Eiji Takahashi of the RIKEN Center for Advanced Photonics (RAP). “They are expected to be used in a wide range of fields, including observing biological cells, developing New Materials and Diagnostic Medical Conditions.”

Strength and momentum

However, although ultrashort laser pulses can be produced, they lack sufficient impact and have low energy. Creating ultra-short and high-energy laser pulses would greatly expand their possible uses. “Currently, the output energy of attosecond lasers is extremely low,” Takahashi said. “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 often use nonlinear crystals that exhibit a special response to light. However, these crystals could be irreparably damaged if they were used to amplify single-cycle laser pulses, which are so short that the pulse ends before the light oscillates through the entire wavelength period.

“The biggest bottleneck in the development of high-energy, ultrafast infrared laser sources is the lack of effective methods to directly amplify single-cycle laser pulses,” Takahashi explained. “This bottleneck leads to a barrier for the energy of single-cycle laser pulses to reach one millijoule. “

new record

Now, Takahashi and RAP colleague Lu Xu have not only broken through this barrier; They have amplified single-cycle pulses to over 50 millijoules, more than 50 times greater than previous best efforts. Because the laser pulses produced are very short, this energy is converted into incredibly high powers of several terawatts.

“We have shown how to overcome the bottleneck by creating an efficient method of amplifying single-cycle laser pulses,” Takahashi said.

Their method, called advanced dual-chirp optical parametric amplification (DC-OPA), is very simple and involves only two crystals that amplify complementary regions of the spectrum.

“The advanced DC-OPA for amplifying single-cycle laser pulses is so simple, based solely on the combination of two nonlinear crystals, that it feels like an idea that anyone can come up with,” Takahashi said. “I was surprised. However, such a simple concept provides a new amplification technology and leads to a breakthrough in the development of high-energy ultrafast lasers.”

Importantly, advanced DC-OPAs operate over a very wide range of wavelengths. Takahashi and Xu were able to amplify pulses with wavelengths that differed by more than a factor of two. “This new method has revolutionary features that enable ultra-wide amplification bandwidth without affecting the output energy scaling characteristics,” Takahashi said.

amplification technology

Their technique is a variation of another light pulse amplification technique called “chirped pulse amplification,” for which three researchers from the United States, France, and Canada won the 2018 Nobel Prize in Physics. There are interesting connections between the Bell Prize in Physics and this technology.

Takahashi expects 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 a single-cycle laser pulse to a terawatt-level peak power,” he said. “This is undoubtedly a major leap forward in the development of high-power attosecond lasers.”

In the long term, his goal is to surpass attosecond lasers and create shorter pulses.

“By combining single-cycle lasers with high-order nonlinear optical effects, it is possible to generate light pulses with a time width of zseconds (one zsecond = 10^{twenty one} Second),” he said. “My long-term goal is to knock on the door of zesecond laser research and develop the next generation of ultrashort lasers after the attosecond laser.