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2D Magnetic Systems
Published in Ram K. Gupta, Sanjay R. Mishra, Tuan Anh Nguyen, Fundamentals of Low Dimensional Magnets, 2023
Second-harmonic generation is a newly established, highly sensitive optical technique that is based on a nonlinear optical process where two photons of the same frequency convert to a single photon of twice the fundamental frequency. This SHG takes place in material systems where inversion symmetry breaks down due to electric dipole approximation. The SHG can be observed in materials that do not possess lattice inversion symmetry (noncentrosymmetric), this process is called “i-type SHG,” as it is time-invariant. When the material is centrosymmetric, then electric dipole allowed SHG can be observed if its magnetism comes into play by breaking both space- and time-reversal symmetries. Hence, reciprocal SHG that does not have time-inversion symmetry, known as “c-type SHG,” can be easily measured to detect AFM order in bulk crystals and surface FM in thin films. Sun et al. have measured strong SHG at 5 K in layered antiferromagnetic CrI3 bilayer (below transition temperature of 40 K) without magnetic field. As the magnetic field of –1 T is applied, the interlayer AFM coupling vanishes due to the alignment of spins in both layers, thereby restoring space- and time-inversion symmetry, and hence no SHG can be observed, thus confirming FM interlayer coupling in CrI3 bilayers at high fields [8, 33].
Future Challenges
Published in Tetsuzo Yoshimura, Self-Organized 3D Integrated Optical Interconnects, 2021
The Pockels effect is an EO effect originated from the second-order nonlinear optical effect. It induces refractive index changes proportional to applied electric fields. The influence of wavefunction shapes on the Pockels effect is predicted using molecular orbital calculations.
Nonlinear Optics
Published in Chunlei Guo, Subhash Chandra Singh, Handbook of Laser Technology and Applications, 2021
Nonlinear optics is the study of the interaction of light with matter under conditions such that the linear superposition principle is not valid. The origin of this breakdown of the linear superposition principle can usually be traced to a modification of the optical properties of the material medium induced by the presence of an intense optical field. With a few exceptions [1], only laser light is sufficiently strong to lead to a significant modification of the optical properties of a material system and, for this reason, the field of nonlinear optics is basically the study of the interaction of laser light with matter. In this context, it is important to distinguish two different sorts of nonlinear optical effects: (i) effects associated with the non-linear optical response of the material contained within the laser cavity itself; and (ii) effects induced by a prescribed laser beam outside of the laser cavity. In this chapter, we are concerned primarily with the second possibility, which constitutes the traditional field of nonlinear optics. Nonlinear optical processes occurring within the laser cavity itself constitute a central aspect of laser physics, as described in Chapter 1, and lead to important effects such as laser instabilities and chaos [2] and self-mode-locking of lasers [3]. The treatment of non-linear optics presented in this chapter is necessarily limited in scope. More detailed treatments can be found in various monographs on the subject [4–10] as well as in the research literature. The present approach follows most closely the notational conventions of Ref. [5].
Investigation of first hyper-polarisability molecular switches between enol–keto equilibrium of phenyl benzodifurantrione: a DFT-based computational study
Published in Molecular Physics, 2023
Usha Mandal, Shashanka Shekhar Samanta, Hasibul Beg, Ajay Misra
Non-linear optical behaviour is observed in materials where the dielectric polarisation reacts nonlinearly to the electric field component of radiation. Second harmonic generation (SHG) [1–4], a nonlinear optical phenomenon that is used in laser as well as optical information processing and data storage devices, doubles the frequency of the incident beam through a NLO active medium [5–11]. For optoelectronic applications, such as molecular-scale memory systems with multiple storage and non-destructive reading capacity, it is very important to find organic materials having commutable NLO responses. In this context, development of NLO switches, or molecules with the capacity to switch between two or more chemical forms that exhibit contrasts in NLO parameter are important in present day research. Over the past 20 years, a wide range of NLO switches with significant alterations in the first hyperpolarisability, the molecular second-order NLO response, have been conceived, synthesised, and described [12–18]. In order to develop molecular switches with significant hyperpolarisability differences, a variety of photochromic chemicals, including azobenzenes [19], diarylethenes [20, 21], benzazolo-oxazolidines [1, 22, 23], anils [24–27], and spiropyrans [28] have been explored both experimentally and theoretically.
3,5-Diethyl-2r,6c-di(4-chlorophenyl)piperidin-4-one picrate: synthesis, spectral, biological, DFT, ADME and molecular docking studies
Published in Molecular Physics, 2022
S. Savithiri, S. Bharanidharan, G. Rajarajan, P. Sugumar, M. Arockia Doss
For new technologies in fields including telecommunications, optical networking and signal processing, nonlinear optics provides essential optical modulation, optical switching, optical logic and optical memory features [28]. The DFT has been extensively used as an effective method to investigate organic NLO material [29]. The dipole moment, molecular polarisability and first-order hyperpolarisability of the DEDCPP molecule were calculated at B3LYP/6-311++G(d,p) basis set and the values are listed in Table 2. The derived values from the dipole moment (μ) are -0.4132925, 1.3316621 and 0.7869526 Debye. In this direction, these calculated values are the equivalent of 1.60107121 Debye. The computed values of polarisability (αij) have nonzero and zero which are subjected to diagonal components. Total polarisability (αtot) was calculated as 0.57674393 × 10−30 esu for the title molecule. The first hyperpolarisability value (β0) of the title compound is 6.44845919 × 10−30 esu, which is ∼17 times greater than that of standard value of urea (β0 = 0.3728 × 10−30esu). The magnitude of molecular hyperpolarisability (β0) is one of the foremost factors contained by an NLO system.
Optically induced birefringence in dye-doped blue phase liquid crystals
Published in Liquid Crystals, 2019
Fen-Chi Lin, Hui-Ying Kuo, Shuan-Yu Huang, Tse-Hsien Wu, Jia-De Lin, Chia-Rong Lee
BP is optically isotropic because the orientations of the molecules in BP could be arbitrary direction [2]. With the exertion of electric field, the local LC molecules in BP reorient and thus the BP becomes optically anisotropic. This phenomenon is known as electro-optic Kerr effect since the induced birefringence is proportional to the square of the applied electric field, which is similar to the Kerr effect in nonlinear optics [12]. Electro-optic Kerr effect is the operation mechanism of electrically controllable photonic devices based on BP and thus have been discussed in previous literatures [13–15]. To realise remotely controllable devices, more and more light responsive photonic devices based on dye-doped BP (DDBP) systems have been demonstrated [11,16–18]. The performance in the photo control of DDBP can be improved via adopting specifically synthesised chiral azobenzene derivatives into BP matrix [19]. Literatures also indicate that the uniformity and electro-optical property of BP with photoalignment layers are superior to pure BP [20]. However, only a few papers investigate the phenomenon of photoinduced index change, such as optical Kerr effect, in DDBP and associated mechanisms [21–23].