Nlo crystals ppt4/18/2023 ![]() In addition to a large first-order hyperpolarizability of the molecules, the macroscopic second order susceptibilities (χ (2)) are strongly dependent on the relative alignment of the π-conjugated chromophores. In general, dipolar molecule units containing highly delocalized conjugated systems and strong electron acceptors (–NO 2, –COOH, –SO 3H, –CN, etc.) and electron donors (–NR 2, –OR, etc.) lead to large molecular first hyperpolarizabilities (β). On the microscopic level, molecular nonlinearity is determined by the molecular structures and their electronic properties. To obtain large second-order NLO effects, it is necessary to investigate both microscopic and macroscopic NLO properties of organic materials. Second harmonic generation (SHG) is a nonlinear optical process, in which photons with the same frequency interacting with a nonlinear material are effectively combined to generate new photons with twice the energy, and therefore twice the frequency and half the wavelength of the initial photons. Among them, single crystals are one of the most attractive materials owing to their typically large macroscopic nonlinearities, high packing densities, and excellent long-term orientational and photochemical stabilities, as well as their superior optical quality. It has become an important research focus to design and synthesize new organic NLO materials with excellent performance. All these advantages make organic NLO materials extremely attractive for the above mentioned applications. ![]() Additionally, the nonlinear optical figures of merit of organic materials may be several orders of magnitude higher than those of their inorganic counterparts and they have almost unlimited design possibilities. This permits an ultra-fast polarizability response time compared to inorganic materials, whose dominant response usually comes from intrinsically slower acoustic and optical lattice vibrations. These materials have low dispersion of their dielectric constants (refractive index) and nonlinear optical susceptibility from direct current (low frequency) to the optical frequency range, because of their dominant electronic contribution to linear and nonlinear optical material polarizability. The recent development of two new-type NLO borate crystals, β-BaB 2O 4 and LiB 3O 5, is described.There has been considerable interest in organic nonlinear optical (NLO) materials with large second-order optical nonlinearities due to their attractive potential applications in optical frequency conversion, integrated photonics, high-speed information processing, and THz wave generation and detection. Suggestions are put forward for searching for and developing other promising new NLO materials in the borate series. On the basis of these structural criteria, we have been successful in developing some new high-quality NLO materials, including the LiB 3O 5 crystal as an excellent NLO material. As a result, the SHG effects will decrease in the order (2) The SHG coefficients can be adjusted to a certain extent by suitable arrangement of the three-and four-coordinated B atoms, such as (BO 3) 3- and (BO 4) 5-, (B 3O 6) 3- as opposed to(B 3O 7) 5- and (B 3O 8) 7. Moveover, in the planar group, the larger the electronic population in the conjugated 7c-orbital system, the greater the SHG effects will be. (1) The planar six-membered ring (B 3O 6) 3- and the planar trigonal (BO 3) 3 group, each possessing a conjugated 7t-orbital system, are far more favourable for producing larger SHG coefficients than the non-planar tetrahedral (BO 4) 5- group. ![]() These structural criteria have good prospects of wider applications in searching and developing for other new types of NLO crystal materials. Through these calculations, a series of structural criteria serving as useful guidelines for searching and developing new NLO crystals in borate series are presented. On this basis, borate ions of various structure types are classified and systematic calculations are carried out for the NLO susceptibilities of some typical borate crystals with good prospects of applications in opto-electronics. Comparisions between these theoretical values and the experimental values made both on powdered crystals and on single crystals suffice to show the feasibility of the theoretical treatment and calculation methods. Calculations have been made for the second harmonic generation (SHG) coefficients of a few typical NLO crystals. Starting from a general quantum-mechanical perturbation theory on the nonlinear optical (NLO) effect in crystals, this review gives a systematic presentation of the basic concepts and calculation methods of the ‘anionic group theory for the NLO effect of crystals’ and a brief discussion of the approximations involved. ![]()
0 Comments
Leave a Reply.AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |