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Progress in theoretical research on deep ultraviolet nonlinear optical properties of inorganic polymer structure bisfluorophosphazene
Progress in theoretical research on deep ultraviolet nonlinear optical performance in China
[ Instrument Network Instrument Development ] Deep-UV nonlinear optical materials play an important role in the practical application of all-solid-state laser technology. However, deep ultraviolet nonlinear optical materials are rare due to stringent performance specifications. KBe2BO3F2 (KBBF) crystal is the only practical deep-UV nonlinear optical crystal material to date, and has very important application value in many high-tech (such as angular resolution spectrometer).
According to the anionic group theory, the deep ultraviolet nonlinear optical properties are rare because the optical band gap and birefringence of most anionic groups cannot simultaneously satisfy sufficiently large conditions. Therefore, most nonlinear optical structures either have a small band gap (such as β-BaB2O4 crystal) and cannot effectively pass through the deep ultraviolet laser, or the birefringence is too low (such as LiB3O5 crystal) to achieve the phase matching necessary for the frequency doubling process. . Therefore, in order to obtain excellent deep-UV nonlinear optical materials, researchers have been hoping to obtain crystal structures with both large band gaps and sufficient birefringence while exhibiting sufficient nonlinear optical effects.
Recently, Lin Zheshuai, a researcher at the Institute of Physics and Chemistry of the Chinese Academy of Sciences, and Dr. Kang Lei, a researcher at the Beijing Center for Computational Science, and researcher Huang Bing, have integrated polar groups with one-dimensional chain characteristics into quasi-one-dimensional polar polymers. In the long chain structure, the structural anisotropy of the nonlinear optical system (and thus the birefringence) is effectively expanded, and the non-bonded orbitals in the structure are greatly saturated (thus increasing the optical band gap).
Under the guidance of this design strategy, the researchers systematically focused on a phosphazene polymer system with a polar chain arrangement and successfully found an experimentally crystalline inorganic polymer structure in the crystal database— - Difluorophosphazene PNF2 - its structure is in line with the theoretical concept of deep ultraviolet non-linear optical polymer materials by researchers working in this work. Moreover, the theoretical calculations of the system show that the bisfluorophosphazene exhibits a large crystal band gap (7.8 to 8.7 eV), a large frequency doubling effect (1.2 to 1.9 times KBBF), and a large birefringence (0.10~). 0.16 at 400 nm) and a shorter deep UV multiplier output wavelength (142 to 158 nm) are a material that is slightly better than KBBF crystals in theoretical performance of deep UV nonlinear optics.
It is worth noting that bisfluorophosphazene is the first non-oxide material and polymer material with deep UV nonlinear optical properties. As a forward-looking theoretical work, it provides a new research idea and strategy reference for the study of deep ultraviolet nonlinear optical materials. The relevant results are published in "Applied Chemistry in Germany" (Angew. Chem. Int. Ed. 10.1002/anie.201905025).
(Original title: Progress in theoretical research on deep ultraviolet nonlinear optical properties of inorganic polymer structure bisfluorophosphazene)