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Analysis of detection methods of photochemical action in laser processing

by:Caodahai     2021-09-28
Laser processing can be divided into laser thermal processing and cold processing according to the mechanism of laser and material. Laser cold processing is also called laser photochemical processing. When laser processing materials, the chemical bonds in the material absorb a single photon or multiple lasers. The energy of the photon initiates or controls the chemical reaction between materials, leading to the breaking and reorganization of chemical bonds in the material, the destruction of the lattice structure or the transition of energy levels, the formation of new substances and the part of the material leaving the body to achieve the purpose of processing. Laser photochemistry is more obvious in short-wavelength ultraviolet laser processing. This type of laser has high photon energy, and material molecules may use single-photon absorption u0026 rdquo; or multi-photon absorption u0026 rdquo;, so that the accumulated photon energy is greater than the intermolecular binding force , The chemical bond of the material is broken; and the laser thermal defect is effectively reduced. Therefore, laser photochemical processing is widely used in the precision and ultra-precision processing of hard and brittle materials.  The photochemical action of the laser on the material produces new substances or changes its composition and structure, and may lead to changes in the physical and chemical properties of the matrix material. Scholars at home and abroad have conducted a large number of experimental studies on laser photochemistry, mainly based on the detection and analysis of the intermediate products, final products and surface morphology of the laser processing process, combined with processing parameters and related properties of materials. This article mainly introduces the various detection and analysis methods used in the study of photochemical effects and processes in the current laser processing process, and analyzes the role of various detection and analysis methods through research cases.  1 Detection and analysis method of laser photochemical action   The mechanism research of laser photochemical action is mainly based on the detection of changes in the structure, composition, physical and chemical properties of the material before and after laser processing, and the analysis of the microscopic observation results of the processed surface. 1.1 The detection and analysis methods for the structural changes of the processed surface At present, the main detection and analysis methods for the structural changes of materials after laser processing, especially crystals and polymer materials, are: Raman spectroscopy, infrared spectroscopy, X-ray diffraction, ultraviolet-visible light absorption spectroscopy, Nuclear magnetic resonance spectroscopy, etc.   Laser photochemical action generates new products mainly through two ways: one is the dissociation reaction, and the other is the isomerization reaction caused by the rearrangement of the molecular skeleton. The essence is that the chemical bonds within or between the molecules of the material are broken or reorganized. The break of molecular bonds always starts from the weaker chemical bonds. Selecting the appropriate wavelength of the laser can cause the dissociation or isomerization of the molecules, and the laser will affect the polymer. The photochemical reaction caused by processing may also include the process of free radical generation, photoionization, and cyclization. Use spectral analysis or X-ray diffraction (crystal) analysis methods to detect and analyze the structural changes of the material after laser processing. The main method is to collect the spectrum or X-ray diffraction pattern of the material before and after the laser action, combined with the material structure knowledge theory and related standards The spectrum is analyzed to determine the structure and phase changes of the material that may be caused by photochemical action in laser processing. In the process of studying polymer materials by 248nm KrF excimer laser, the Raman spectra of PMMA, PTFE and other polymer materials before and after etching were analyzed, and it was found that PTFE had a broadband structure caused by Cu003dC after laser etching. , Corresponding to fluorine-containing polyene compounds of different chain lengths and chemical formulas. In the process of studying the polymer modified by excimer laser, Ji Yaling used XRD analysis and Raman spectroscopy on the surface of PVDF and other materials before and after laser irradiation, and found that PVDF samples showed obvious changes such as new Raman peaks after laser irradiation Infrared spectroscopy detection and analysis found that the crystal phase and chemical composition of PVDF changed before and after the laser action; it was confirmed that the 248nm KrF excimer laser had a photochemical reaction with PVDF, which eventually led to the chemical bond and molecular structure of PVDF polymer material. Variety. The use of spectroscopic detection and X-ray diffraction analysis to study structural changes has been widely used in laser processing of various polymer materials and transparent media of crystal materials. (The above is edited and compiled by the metal laser cutting machine on the Internet. For details, see www.gnlaser.com)
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