Ultrafast Laser - Chasing The Limit of Time

Ultrafast laser is the new "commanding heights" of laser technology in recent years. In 2023, Pierre Agostini, Ferenc Kraus and Anne Lullier won the Nobel Prize in Physics for their experimental method of generating attosecond light pulses by studying the dynamics of electrons in matter. , also pushed the research on ultrafast lasers to a new craze.

What is an ultrafast laser?

Ultrafast laser refers to a pulse laser with a pulse width of picosecond level or less. It is named because the pulse width is extremely short and the pulse time is extremely fast.

What is a picosecond? Picosecond, femtosecond and attosecond are all very small units of time. 1 picosecond is equivalent to 10^-12 seconds, and 1 femtosecond is equivalent to 10^-15 seconds. The attosecond laser that won the Nobel Prize last year The "attosecond" is equivalent to 10^-18 seconds.

Such a minute unit of time is far smaller than people's perception. To give an example that is easier for people to understand, the time comparison between one attosecond and one second is equivalent to the time comparison between one second and the lifetime of the universe.

Ultrafast laser has both ultrafast time domain characteristics and ultrafast peak characteristics. It can create unprecedented extreme physical conditions such as ultrafast time, ultrahigh intensity field, ultrahigh temperature and ultrahigh pressure. It is an important factor in promoting plasma physics, atomic and molecular physics. It is an important basic scientific research tool for the development of disciplines such as particle physics and nuclear physics, and it also brings a new key to high-end manufacturing, aerospace, biomedicine and other fields.

Ultrafast laser, what’s so powerful about it?

We know that according to the energy output waveform, laser can be divided into two types: continuous laser and pulse laser. Continuous laser has constant output power, while the power of pulse laser changes at any time, with peak value and pulse width.

If certain technical means are used to concentrate the laser energy on a single pulse, the instantaneous power can be greatly increased while the average laser power remains unchanged, thus meeting the needs of material processing. With the deepening of research, people gradually discovered that pulse laser has unique advantages in processing accuracy. This is because the thermal effect of pulse laser on the material is smaller, which is similar to "cold processing", and the processed aperture formed is smoother and more beautiful.

If the pulse can be compressed to a shorter time, such as the "picosecond", "femtosecond" or even "attosecond" levels just mentioned, on the one hand, the power can be more concentrated, and on the other hand, the processing effect can be optimized. In order to enable ultrafast lasers to stably output ultrashort pulses, mode locking technology can be used. In order to obtain higher pulse energy, CPA amplification technology (chirped pulse amplification technology) is needed, which is also the research direction of the Nobel Prize winner.

Applications of ultrafast lasers

Ultrafast lasers have a wide range of applications. Downstream industries such as ultra-fast measurement, precision manufacturing, precision medicine, femtosecond chemicals, and laser display have unprecedented output values that need to be further explored. Here are just two basic examples that have been applied in practice.

Ultrafast lasers have important applications in the medical field, such as the all-femtosecond laser myopia surgery that we are relatively familiar with. Among various types of myopia correction surgeries, all-femtosecond laser surgery has become the mainstream method for treating myopia. It uses femtosecond laser to create corneal flaps and accurately cut the corneal stroma. Compared with excimer laser surgery, all-femtosecond laser myopia surgery has become the mainstream method for treating myopia. It has high accuracy, no obvious pain, and good visual recovery after surgery.

Ultrafast lasers are also suitable for processing hard and brittle materials in consumer electronics. The polymer material used in OLED screens is sensitive to heat and is easily deformed due to thermal effects; while the sapphire material used in smart watches, mobile phone camera covers, etc. has high hardness and brittleness, and is prone to chipping and chipping during mechanical processing. For these materials, ultrafast laser processing can reduce thermal effects and ensure material yield.

Current status of ultrafast lasers

my country's ultrafast laser research started late, and the global advanced level of ultrafast laser technology is controlled by a few institutions and companies, mainly concentrated in developed countries such as the United States, Germany, France, and the United Kingdom. As of 2022, my country's overall ultrafast laser import rate will exceed 80%, and the import dependence rate of core ultrafast laser components is still high.

Due to the high threshold of ultrafast laser technology, domestic substitution, especially the localization of ultrafast laser-related components, needs further exploration. The good news is that companies such as Han's Laser, Inno Laser, Huari Laser, and JPT are committed to the industrialization of ultrafast lasers. The Institute of Physics of the Chinese Academy of Sciences, Shanghai Institute of Optics and Mechanics, Xi'an Institute of Optics and Mechanics, Tsinghua University, and Huazhong University of Science and Technology Scientific research institutes and universities are also investing in technological research. It is expected that driven by the demand side and improved reliability, domestic ultrafast lasers can break away from the low-price route and achieve industry leadership.