Organic Nonlinear Optical Crystals for Highly Efficient Terahertz-Wave Generation

Abstract

Terahertz (THz) technology is an emerging field that is promising for future applications. Nonlinear optical (NLO) materials can effectively convert incident light into the THz frequency range using optics methods. Ionic-type organic π-conjugated NLO crystals containing electron donor-π-acceptor motifs have long attracted attention for their possibility to achieve large nonlinear optical coefficients. In this paper, an overview of the recent progress in ionic-type organic NLO crystals for highly efficient THz wave generation is presented. The substitution design strategies of cations and anions, for increasing optical nonlinearities and reducing absorptions in different structure series, are summarized. In addition, the progress in crystal growth and their THz output performance are also discussed.

Crystal Growth, Optical, Thermal, DFT and Z‐Scan Studies of Imidazolium Hydrogen Fumarate Crystal for Nonlinear Optical Applications

“…[6,7] Organic NLO crystals often exhibit good optical nonlinearity compared to inorganic crystals. [8,9] Organic materials were recognized as an alternative to inorganic materials because of their promising physical characteristics, such as high NLO susceptibility, high laser damage threshold, high birefringence, strong elasticity, good optical characteristics, molecular flexibility, low mobility, ease of manufacturing, and wide bandgap value. [10,11] Femtosecond laser pulses, Z-scan method and hyper-Rayleigh scattering are frequently used for the measurement of the NLO properties in the near-infrared region.…”

“…So, the cations are the primary cause of nonlinearities. [9,17] In the ionic type of crystal, D-𝜋-A is the basic structure of the cation. The 𝜋conjugated bond connects both the electron acceptor (A) and electron donor (D) part.…”

Symmetry Reduction of Molecular Shape of Cationic Chromophores for High‐Performance Terahertz Generators

“…[1][2][3][4][5] Organic nonlinear optical crystals provide great potential for use in the development of various types of THz devices such as generators and detectors, as well as high-speed optical modulators. [6][7][8][9][10][11][12][13][14][15][16][17][18][19] This is due to their unique dielectric dispersion properties and high optical nonlinearities compared to more commonly used inorganic crystals. However, designing suitable organic nonlinear optical crystals for THz devices is still extremely challenging.…”

New Organic Nonlinear Optical Pyridinium-Based Hydrate Crystals: Trimethoxy-Induced Noncentrosymmetric Alignment

“…In the design of the D–π–A-type structure of cation chromophore, different substituents are usually selected as the electron donor (such as –OH, –OCH 3 , –N­(CH 3 ) 2 ...) or acceptor (pyridinium, quinolinium, benzothiazolium, indolinium...) to modify the delocalized π conjugation system to balance the varying performance of the crystals. ,− Particularly, selecting the methoxy electron donor is beneficial to the macro NLO effect, such as the reported 4-methoxybenzaldehyde- N -methyl-4-stilbazolium tosylate (MBST) crystals, which has a high powder second harmonic generation (SHG) efficiency 17 times that of urea. , Subsequently, the 3,4-dimethoxybenzaldehyde- N -methyl-4-stilbazolium tosylate (DOST) crystals with dimethoxy groups were reported to also have a high SHG efficiency of 21 times that of standard KDP …”