The development and application of femtosecond laser technology
2021-12-15
Since Maman first obtained laser pulse output in 1960, the process of human compression of laser pulse width can be roughly divided into three stages: Q-switching technology stage, mode-locking technology stage, and chirped pulse amplification technology stage. Chirped pulse amplification (CPA) is a new technology developed to overcome the self-focusing effect generated by solid-state laser materials during femtosecond laser amplification. It first provides ultra-short pulses generated by mode-locked lasers. "Positive chirp", expand the pulse width to picoseconds or even nanoseconds for amplification, and then use the chirp compensation (negative chirp) method to compress the pulse width after obtaining sufficient energy amplification. The development of femtosecond lasers is of great significance. Before 1990, femtosecond laser pulses had been obtained using dye laser mode-locking technology with wide gain bandwidth. However, the maintenance and management of the dye laser is extremely complicated, which limits its application. With the improvement of the quality of Ti:Sapphire crystals, shorter crystals can also be used to obtain sufficiently high gains to achieve short pulse oscillation. In 1991, Spence et al. developed a self-mode-locked Ti:Sapphire femtosecond laser for the first time. The successful development of a 60fs pulse width Ti:Sapphire femtosecond laser greatly promoted the application and development of femtosecond lasers. In 1994, the use of chirped pulse amplification technology to obtain laser pulses less than 10fs, currently with the help of Kerr lens self-mode locking technology, optical parametric chirped pulse amplification technology, cavity emptying technology, multi-pass amplification technology, etc. can make laser The pulse width is compressed to less than 1fs to enter the attosecond domain, and the peak power of the laser pulse is also increased from terawatt (1TW=10^12W) to petawatt (1PW=10^15W). These major breakthroughs in laser technology have triggered extensive and in-depth changes in many fields. In the field of physics, the ultra-high-intensity electromagnetic field generated by the femtosecond laser can generate relativistic neutrons, and can also directly manipulate atoms and molecules. On a desktop nuclear fusion laser device, a femtosecond laser pulse is used to irradiate deuterium-tritium molecular clusters. It can initiate a nuclear fusion reaction and produce a large number of neutrons. When the femtosecond laser interacts with water, it can cause the hydrogen isotope deuterium to undergo a nuclear fusion reaction, generating huge amounts of energy. Using femtosecond lasers to control nuclear fusion can obtain controllable nuclear fusion energy. In the Universe Physics Laboratory, high-energy-density plasma generated by ultra-high-intensity light pulses of femtosecond lasers can reproduce the internal phenomena of the Milky Way and stars on the ground. The femtosecond time resolution method can clearly observe the changes of the molecules placed in nanospace and their internal electronic states on the time scale of femtoseconds. In the field of biomedicine, due to the high peak power and power density of femtosecond lasers, various non-linear effects such as multiphoton ionization and self-focusing effects are often caused when interacting with various materials. At the same time, the interaction time between the femtosecond laser and biological tissues is insignificant compared to the thermal relaxation time of biological tissues (on the order of ns). For biological tissues, a temperature rise of a few degrees will become a pressure wave to the nerves. The cells produce pain and heat damage to the cells, so the femtosecond laser can achieve painless and heat-free treatment. Femtosecond laser has the advantages of low energy, small damage, high accuracy and strict positioning in three-dimensional space, which can meet the special needs of the biomedical field to the greatest extent. The femtosecond laser is used to treat teeth to obtain clean and tidy channels without any edge damage, avoiding the influence of mechanical stress and thermal stress caused by long pulse lasers (such as Er:YAG), calcification, cracks and rough surfaces. When the femtosecond laser is applied to the fine cutting of biological tissues, the plasma luminescence during the interaction of the femtosecond laser with biological tissues can be analyzed by spectrum, and bone tissue and cartilage tissue can be identified, so as to determine and control what is needed in the surgical treatment process Pulse energy. This technique is of great significance for nerve and spine surgery. The femtosecond laser with a wavelength range of 630-1053nm can perform safe, clean, high-precision non-thermal surgical cutting and ablation of human brain tissue. A femtosecond laser with a wavelength of 1060nm, a pulse width of 800fs, a pulse repetition frequency of 2kHz, and a pulse energy of 40μJ can perform clean, high-precision corneal cutting operations. Femtosecond laser has the characteristics of no thermal damage, which is of great significance for laser myocardial revascularization and laser angioplasty. In 2002, the Hannover Laser Center in Germany used a femtosecond laser to complete the breakthrough production of vascular stent structure on a new polymer material. Compared with the previous stainless steel stent, this vascular stent has good biocompatibility and biological compatibility. Degradability is of great significance to the treatment of coronary heart disease. In clinical testing and bioassays, femtosecond laser technology can automatically cut the biological tissues of organisms at the microscopic level, and obtain high-definition three-dimensional images. This technology is of great significance for the diagnosis and treatment of cancer and the study of animal 368 genetic mutations. In the field of genetic engineering. In 2001, K.Konig of Germany used Ti:Sapphire femtosecond laser to perform nanoscale operations on human DNA (chromosomes) (minimum cutting width 100nm). In 2002, U.irlapur and Koing used a femtosecond laser to make a reversible micropore in the cancer cell membrane, and then allowed DNA to enter the cell through this hole. Later, the cell's own growth closed the hole, thus successfully achieving gene transfer. This technique has the advantages of high reliability and good transplantation effect, and is of great significance for transplanting foreign genetic material into various cells including stem cells. In the field of cell engineering, femtosecond lasers are used to achieve nano-surgery operations in living cells without damaging the cell membrane. These femtosecond laser operation techniques have positive significance for the research of gene therapy, cell dynamics, cell polarity, drug resistance, and the different components of cells and subcellular heterogeneous structure. In the field of optical fiber communication, the response time of semiconductor optoelectronic device materials is the "bottleneck" that restricts super-commercial speed optical fiber communication. The application of femtosecond coherent control technology makes the speed of semiconductor optical switches reach 10000Gbit/s, which can finally reach the theoretical limit of quantum mechanics. . In addition, the Fourier waveform shaping technology of femtosecond laser pulses is applied to large-capacity optical communications such as time division multiplexing, wavelength division multiplexing and code division multiple access, and a data transmission rate of 1Tbit/s can be obtained. In the field of ultra-fine processing, the strong self-focusing effect of femtosecond laser pulses in transparent media makes the laser focal spot smaller than the diffraction limit, causing micro-explosions inside the transparent material to form stereo pixels with sub-micron diameters. Using this method, high-density three-dimensional optical storage can be performed, and the storage density can reach 10^12bits/cm3. And can realize fast data reading, writing, and parallel data random access. The crosstalk between adjacent data bit layers is very small, and three-dimensional storage technology has become a new research direction in the development of current mass storage technology. Optical waveguides, beam splitters, couplers, etc. are the basic optical components of integrated optics. Using femtosecond lasers on a computer-controlled processing platform, two-dimensional and three-dimensional optical waveguides of any shape can be made at any position inside the material. , Beam splitter, coupler and other photonic devices, and can be coupled with standard optical fiber, using femtosecond laser can also make 45 ° micro-mirror inside the photosensitive glass, and now an optical circuit composed of 3 internal micro-mirrors has been produced , Can make the beam rotate 270° in the area of 4mmx5mm. More scientifically, scientists in the United States have recently used femtosecond lasers to create a 1cm-long gain optical waveguide, which can generate a signal gain of 3dB/cm near 1062nm. Fiber Bragg grating has effective frequency selection characteristics, is easy to couple with fiber communication system and has low loss. Therefore, it exhibits rich transmission characteristics in the frequency domain and has become a research hotspot of fiber optic devices. In 2000, Kawamora K et al. used two infrared femtosecond laser interferometry to obtain surface relief holographic gratings for the first time. Later, with the development of production technology and technology, in 2003 Mihaiby. S et al. used Ti:Sapphire femtosecond laser pulses combined with zero-order phase plates to obtain reflective Bragg gratings on the core of communication fibers. It has a high refractive index modulation range and good temperature stability. The photonic crystal is a dielectric structure with periodic modulation of refractive index in space, and its change period is the same order of magnitude as the wavelength of light. The photonic crystal device is a brand-new device that controls the propagation of photons, and has become a research hotspot in the field of photonics. In 2001, Sun H B et al. used femtosecond lasers to fabricate photonic crystals with arbitrary lattices in germanium-doped silica glass, which can individually select individual atoms. In 2003, Serbin J et al. used femtosecond laser to induce two-photon polymerization of inorganic-organic hybrid materials to obtain three-dimensional microstructures and photonic crystals with a structure size of less than 200nm and a period of 450nm. Femtosecond lasers have achieved breakthrough results in the field of microphotonic device processing, so that directional connectors, bandpass filters, multiplexers, optical switches, wavelength converters, and modulators can be processed on a "chip" Planar lightwave loops with other components are possible. Laid a foundation for photonic devices to replace electronic devices. Photomask and lithography technology is a key technology in the field of microelectronics, which is directly related to the quality and production efficiency of integrated circuit products. Femtosecond lasers can be used to repair the defects of the photomask, and the repaired line width can reach an accuracy of less than 100nm. The femtosecond laser direct writing technology can be used to quickly and effectively manufacture high-quality photomasks. These results are very important for micro The development of electronic technology is of great significance.
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