In the ever-evolving landscape of scientific exploration, the realm of ultrafast phenomena stands as a testament to human ingenuity and technological advancement. Among the myriad tools in the scientist’s arsenal, one particular marvel has emerged as a cornerstone of ultrafast science: the femtosecond. In this article, we delve into the fascinating world of femtosecond technology, exploring its significance, applications, and the profound insights it offers into the fundamental nature of matter and energy.
The Define Of Femto Second
At its core, a femtosecond is an incredibly brief unit of time, equivalent to one quadrillionth of a second, or 10−1510−15 seconds. To put this staggering scale into perspective, it’s akin to comparing a second to about 31.71 million years!
Such fleeting intervals of time may seem inconceivable, yet they hold the key to unlocking a wealth of scientific mysteries.The advent of femtosecond technology has revolutionized various fields, from physics and chemistry to biology and material science.
The advent of femtosecond technology has revolutionized various fields, from physics and chemistry to biology and material science. One of its most prominent applications lies in ultrafast laser spectroscopy, where pulses lasting just femtoseconds enable researchers to probe the dynamics of molecular and atomic processes with unprecedented temporal resolution. This capability has unveiled the intricate dance of electrons within atoms, shedding light on phenomena such as chemical reactions, electron transfer processes, and even the behavior of exotic materials under extreme conditions.
In the realm of optics, femtosecond lasers have paved the way for breakthroughs in nonlinear optics and photonics. By harnessing the intense, ultrashort pulses emitted by femtosecond lasers, scientists can manipulate light in novel ways, leading to advancements in fields like telecommunications, laser machining, and medical imaging. Moreover, femtosecond lasers have enabled the development of powerful tools such as two-photon microscopy, which allows for high-resolution imaging deep within biological tissues, revolutionizing our understanding of cellular processes and disease mechanisms.Beyond its applications in research and technology, femtosecond science holds profound implications for fundamental physics.
The ability to observe and control phenomena unfolding at femtosecond timescales has led to groundbreaking discoveries in fields such as quantum mechanics, ultrafast optics, and laser physics.Moreover, femtosecond technology plays a crucial role in the emerging field of attosecond science, where scientists seek to probe phenomena occurring on timescales even shorter than a femtosecond, delving into the realm of electron dynamics within atoms and molecules.
Despite its remarkable capabilities, harnessing femtosecond technology poses significant challenges. The generation and manipulation of ultrashort pulses require intricate laser systems and precise control mechanisms, pushing the boundaries of current engineering and manufacturing capabilities. Moreover, the extreme intensities associated with femtosecond pulses demand careful attention to safety considerations, both in laboratory settings and in practical applications.
Looking ahead, the future of femtosecond science holds immense promise. As technology continues to advance, researchers strive to push the limits of temporal resolution, unraveling ever more elusive mysteries at the heart of the quantum world. From unraveling the secrets of photosynthesis to revolutionizing precision surgery, the impact of femtosecond technology resonates across diverse fields, shaping the forefront of scientific inquiry and innovation.
The Features Of Femto Second
Lasers were once regarded as mysterious lights and have been widely used by humans. In recent years, scientists have discovered a more peculiar laser – femtosecond laser. Femtosecond, also called femtosecond, or fs for short, is a unit of measurement for measuring the length of time. Technical means to obtain the shortest pulse under laboratory conditions.
The huge power emitted by femtosecond laser in an instant is greater than the total power generated in the world. It has been used in some applications. Scientists predict that femtosecond laser will play an important role in the generation of new energy in the next century.Femtosecond laser has the following characteristics:
- First, the duration of femtosecond laser is extremely short, only a few femtoseconds. It is thousands of times shorter than the shortest pulse obtained by electronic methods, and is the shortest pulse that humans can obtain under experimental conditions;
- Secondly, femtosecond laser has very high instantaneous power, which can reach one million watts, which is hundreds of times more than the total power generation in the world;
- Third, femtosecond lasers can focus into a space area smaller than the diameter of a hair, making the intensity of the electromagnetic field several times higher than the force of the atomic nucleus on the surrounding electrons. Many of these extreme physical conditions are on Earth. What does not exist and cannot be obtained by other methods. Due to the ultra-high peak power of femtosecond laser, after focusing, its light intensity can reach the level of 1022W/cm2. This intensity far exceeds the Coulomb field of the internal interaction of atoms, so femtosecond laser pulses can easily break electrons away from atoms and form plasma. For example, the Coulomb field strength of hydrogen atoms is 5×1011V/m, and a 1m J femtosecond laser pulse can reach the level of 1012V/m after focusing, so it can ionize hydrogen atoms.
The History Of Femto Second
Femtosecond laser cutting technology continues to develop with the advancement of science and technology. Its pulse width is getting shorter and shorter, and the peak power of the pulse is getting larger and larger.
- Since the advent of the first ruby laser in 1960, shortening laser pulses has become an important development direction in laser design and production. In order to shorten the laser pulse, laser mode locking technology was proposed from the late 1960s to the early 1970s, and the generation of femtosecond laser originated from this technology.
- In 1974, E.P. Ippen and others invented the extracavity grating pair compression technology and obtained femtosecond laser pulses for the first time through dye lasers.
- In 1981, R.L. Fork et al. obtained a 90fs laser pulse from a dye laser through collision pulse mode locking technology.
- However, the dye laser has a complex structure, requires a dye circulation system, and its gain bandwidth is narrow. It can only be studied under laboratory conditions and cannot be widely used. Therefore, after the emergence of solid lasers, especially titanium sapphire crystal lasers, they were quickly eliminated.
- In 1983, D. E. Spence and others invented self-mode locking technology, also known as Kerr lens mode locking. The characteristic of this technology is that it does not require additional pulse mode locking.
- In 1981, people from the US laboratory first used collision mode locking technology (in a ring dye laser to obtain ultra-short laser pulses with a pulse width of only 10%). In 1985, people from the laboratory introduced into the laser cavity a method that could compensate for intra-cavity group velocity dispersion. The four-prism structure and the ultra-short laser pulse obtained have greatly promoted the development of ultra-short pulse technology.
- In 1985, Strickland and Mourou proposed the chirped pulse amplification theory, laying a theoretical foundation for the development of femtosecond lasers.
- In 1989, P. N. Kea and others invented the coupling cavity mode locking technology, also known as additional pulse mode locking, and obtained laser pulses of hundreds of femtoseconds.
- In 1991, D. E. Spence and others used self-mode-locking technology and used titanium-doped sapphire as the gain medium to obtain a 60-femtosecond laser pulse. This is regarded as the first true femtosecond laser pulse in human history. . In the same year, A.Sullivan et al. obtained a laser pulse of 100fs and a peak power of 3TW. Lasers using titanium sapphire crystal as the gain medium have the advantages of simple structure, stable performance, long working life, high peak power, wide tuning range, and wide application. Therefore, it quickly replaced the status of dye lasers and developed rapidly. 
- In 1993, M.T. Aaki et al. used titanium-doped sapphire laser self-mode-locking technology to obtain 11fs laser pulses. Similarly, Washington State University in the United States and the University of Vienna in Austria obtained 10fs laser pulses.
- In 1996, C.P.J.Barry et al. used regenerative amplification pulse shaping and high-order dispersion compensation technology to obtain a pulse width of 18 fs and a peak power pulse output of 4.4TW.
- In 1997, U.Keller et al. obtained a 6.5fs laser pulse by combining chirp technology with a prism. In the same year, Stuart et al. used a neodymium glass amplifier to obtain a laser pulse of 395fs and a peak power of 125TW. In 1999, Perry et al. improved the neodymium glass amplifier and obtained a laser pulse of 440fs with a peak value exceeding 1.5PW.
- In 2004, a research team from Hokkaido University in Japan used optical fibers to broaden and then compress the pulse spectrum output from a chirped amplification system, and obtained a femtosecond laser pulse with a pulse width of 2.8fs. In the same year, the Shanghai Institute of Optics and Mechanics of the Chinese Academy of Sciences successfully obtained a laser pulse of 36fs and a peak power of 120TW using its own titanium sapphire crystal.
- In recent research, researchers from the University of Vienna in Austria, the National Research Center of Canada, and the University of Bielfeld in Germany have successfully obtained 650 angstrom-second (as) laser pulses using strong-field high-order harmonic technology. This brought a leap forward in the development of lasers. Due to the characteristics of femtosecond laser, including short pulse, high energy and high peak power, it has broad prospects in application. Femtosecond laser technology has been widely used in various fields such as environment, information, medical care, national defense, and industry.
- Femtosecond laser is a laser that operates in the form of pulses. Its duration is very short, only a few femtoseconds. One femtosecond is 10 to the power of minus 15 seconds, which is 1/1000 trillion seconds. It is faster than the use of electronics. The shortest pulses obtained by this method are thousands of times shorter. This is the first feature of femtosecond laser. The second characteristic of femtosecond laser is that it has very high instantaneous power, which can reach one million watts, which is a hundred times more than the total power generation in the world. The third characteristic of femtosecond laser is that it can focus on a spatial area smaller than the diameter of a hair, making the intensity of the electromagnetic field several times higher than the force of the atomic nucleus on the surrounding electrons.
- On February 4, 2024, it was learned from the University of Science and Technology of China that the research group of Li Jiawen, associate professor of the Micro-Nano Engineering Laboratory of the School of Engineering Science, proposed a femtosecond laser dynamic holographic processing method suitable for the efficient construction of three-dimensional capillary scaffolds, and used it to print Three-dimensional capillary network. The results have been published in “Advanced Functional Materials” and the related technology has been patented.
The Advantages Of Manufacturing Materials
Compared with traditional continuous laser and long pulse width (nanosecond, picosecond laser), femtosecond laser processing materials has the following characteristics:
- High peak power can easily cause dissociation of materials. Taking the titanium sapphire femtosecond laser with a regenerative amplification system produced by Spectrum as an example, its pulse width is , the repetition frequency is a single pulse energy, and its laser pulse peak can reach the order of magnitude. The peak power of femtosecond laser pulses obtained by using multi-level chirped pulse amplification technology has reached orders of magnitude. When a strong femtosecond laser interacts with a material, the material can dissociate within hundreds of femtoseconds.
- It has small thermal effect and high processing accuracy, and has unique advantages in precision processing of materials. When laser interacts with matter, the size of the thermal effect is closely related to the pulse width of the laser. Generally speaking, when a laser acts on a material, the energy is first absorbed by the excited electrons, and then the energy is transferred to the crystal lattice through electron lattice scattering. Usually the time scale of this process is tens of picoseconds, and then the heat is transferred to the crystal lattice. It is transferred between lattice, causing the surrounding lattice temperature to rise, causing phase change, flame and vaporization of the material. For nanosecond lasers, since the pulse width is much larger than the time for electron lattice scattering, during the pulse action, the energy has enough time to be transferred from the electrons to the lattice and diffuse between the lattice, making the lattice Melting and vaporization occur as the temperature gradually increases. The difference is that the pulse width generated by the femtosecond laser is even shorter. At this time, the action time of the pulse is much shorter than the time of electron lattice scattering. When the laser pulse action is completed, the energy is too late to be transferred to the lattice. Therefore, The crystal lattice is “cold”. The material dissociation caused by femtosecond laser occurs within a few picoseconds, and the material dissociation process caused is relatively complicated. There are two main types of material dissociation mechanisms: Coulomb explosion and phase explosion. When picosecond pulse laser interacts with materials, the thermal effect produced is between nanosecond laser and femtosecond laser.
- Wide range of applications. Modern research has applied femtosecond laser processing to many solid materials, ranging from metals, semiconductors, dielectrics and polymers. Moreover, the development of femtosecond lasers is also quite rapid. The waveband covers rays to near-infrared, and the pulse width ranges from several femtoseconds to hundreds of femtoseconds, which can meet the processing needs of various materials. Especially in recent years, femtosecond lasers have tended to be miniaturized and integrated, and the output laser power has become more stable and reliable, which has enabled femtosecond lasers to successfully move from laboratories to factories.
The Application Of Femto Second
What are the uses of femtosecond laser? As we all know, matter is composed of molecules and atoms, but they are not static and are moving rapidly. This is a very important basic property of microscopic matter. The emergence of femtosecond lasers enabled humans to observe this ultrafast motion process at the atomic and electron level for the first time. Based on these scientific discoveries, femtosecond lasers have been widely used in fields such as physics, biology, chemical control reactions, and optical communications. It is particularly worth mentioning that due to its fast and high-resolution characteristics, femtosecond laser has its unique advantages and is irreplaceable in early diagnosis of lesions, medical imaging and biological detection, surgical treatment and the manufacturing of ultra-small satellites. role.
In the field of micromachining, because it has minimal impact on the surrounding materials, it can safely cut, drill, and engrave, and can even be used in the photolithography process of integrated circuits. In the field of national defense, femtosecond lasers are used in safely cutting high explosives and dismantling old and decommissioned rockets and artillery shells. In the medical field, femtosecond laser is like a precise scalpel and is used to treat myopia, cosmetics, etc. In biology, femtosecond lasers bombard cellular DNA, causing it to mutate, and are used to study the various effects of genetic changes. In the environmental field, femtosecond laser LIBS technology measures atmospheric pollution components and detects environmental pollution levels. In the field of scientific research, femtosecond lasers are everywhere. With the development of femtosecond laser technology, femtosecond laser can find more applications in more fields.
Under the action of high-intensity femtosecond laser, substances will undergo very strange phenomena: gaseous, liquid, and solid substances instantly turn into plasma. This plasma can radiate laser light of various wavelengths. The collision of high-power femtosecond laser and electron beam can produce hard X-ray femtosecond laser, produce beta-ray laser, and produce positron and negative electron pairs.
High-power femtosecond lasers have good development prospects in medicine, ultra-fine microprocessing, and high-density information storage and recording. High-power femtosecond lasers can also penetrate the atmosphere to create discharge channels and achieve artificial lightning triggering, thus avoiding catastrophic damage caused by natural lightning strikes to aircraft, rockets, and power plants. The use of femtosecond lasers can accelerate electrons very effectively, compressing the size of the accelerator thousands of times. High-power femtosecond laser interacts with matter and can produce a sufficient number of neutrons to achieve rapid ignition of laser-controlled nuclear fusion. This will open up a new way for mankind to realize a new generation of energy.