Molecular Structures and Second-Order Nonlinear Optical Properties of Ionic Organic Crystal Materials

Abstract

Abstract:In recent years, there has been extensive research and continuous development on second-order nonlinear optical (NLO) crystal materials due to their potential applications in telecommunications, THz imaging and spectroscopy, optical information processing, and optical data storage. Recent progress in second-order NLO ionic organic crystal materials is reviewed in this article. Research has shown that the second-order nonlinear optical properties of organic crystal materials are closely related to their molecular structures. The basic structures of ionic organic conjugated molecules with excellent nonlinear optical properties are summarized. The effects of molecular structure, for example, conjugated π electron systems, electronic properties of donor-acceptor groups, and different counter-anion effects on second order NLO properties and crystal packing are studied.

Organic Crystals for THz Photonics

“…Additional to the much superior temporal stability of crystals compared to poled polymers, their photochemical stability may be better by several orders of magnitude [29], which is particularly important for THz-wave applications, where high optical power densities are used and therefore a high damage threshold is required. On the other hand, only a very small ratio of known chromophores can crystallize in a non-centrosymmetric crystalline space group and there seems to be a limit in the conjugation length (i.e., the first hyperpolarizability strength β) that can still lead to a non-centrosymmetric alignment [15,30]. The chromophores, besides having a large β, need to be usually specially designed to promote a non-centrosymmetric alignment [15,30].…”

Continuous Generation of Millimeter-Sized Glycine Crystals in Non-Seeded Millifluidic Slug Flow

“…For a similar condition in batch cooling crystallization (with initial temperature of 35 • C and final temperature of 20 • C) [59], crystals with an average size of circa 600 µm were generated after 20 min to 6 h [60,61], and here, only 10 min were needed. Although glycine was the compound used here, a similar strategy (e.g., suppressing secondary nucleation) may potentially help generate large crystals of other compounds [62][63][64][65][66][67][68][69][70][71][72].…”

Borates—Crystal Structures of Prospective Nonlinear Optical Materials: High Anisotropy of the Thermal Expansion Caused by Anharmonic Atomic Vibrations

“…Double 5B-groups <3B>-<3B> composed of two 3B-rings via a common tetrahedron (see Figure 1, 5B) occur quite frequently for instance 5B:4∆1 :<2∆ >-<2∆ > in K[B 5 Thermal variations of B-O-B angles. As defined in Section 2.1 a rigid group is devoid of internal degrees of freedom whilst the external degrees of freedom of a rigid group change as impact on temperature.…”

“…Studies have shown that the second-order NLO properties of crystalline materials are closely related to their structures. Tens of inorganic and organic ( [2][3][4][5], and Refs therein) crystals with NLO properties were identified, and their crystal structures, micro-structures, and various properties were studied. Nevertheless, there is growing interest in the search for new, prospective NLO materials due to the widening technical applications as a result of the replacement of gaseous and ionic laser sources with solid lasers.…”