Optik - International Journal for Light and Electron Optics 248 (2021) 168196 Available online 20 October 2021 0030-4026/© 2021 Elsevier GmbH. All rights reserved. All optical switching and the optical nonlinear properties of 4-(benzothiazolyldiazenyl)-3-chlorophenyl 4-(nonylthio)benzoate (EB-3Cl) Uhood J. Al-Hamdani a , Qusay M.A. Hassan b, * , C.A. Emshary b , H.A. Sultan b , Adil Muala Dhumad a , Afrah A. Al-Jaber a a Department of Chemistry, College of Education for Pure Sciences, University of Basrah, Basrah 61001, Iraq b Department of Physics, College of Education for Pure Sciences, University of Basrah, Basrah 61001, Iraq A R T I C L E INFO Keywords: DRPs Z-scan INR OLg Fresnel-Kirchhoff integral ABSTRACT Chemical computational calculations are carried out to investigate the molecular structure of 4- (benzothiazolyldiazenyl)-3-chlorophenyl 4-(nonylthio)benzoate (EB-3Cl) via the density func- tional theory (DFT) method. The B3LYP method is used to optimize the geometrical structure of the EB-3Cl compound with 6–31G(d,p) basis set level. HOMO-LUMO energies and some nonlinear optical (NLO) properties are calculated via the same method used in geometry optimization. The results show that the synthesized compound has good optical properties. Good agreement cor- relations of experimental and theoretical findings are found. The index of nonlinear refraction (INR) of EB-3Cl is determined via two methods, the diffraction ring pattern (DRP) and the Z-scan. High INR value of 5.92×10  7 cm 2 /W is obtained via the first method. Optical limiting (OLg), of the synthesized compound is studied with OLg threshold value of 8 mW is obtained. All optical switching technique is tested in the prepared compound with good results are obtained and DRPs are simulated numerically based on the Fresnel-Kirchhoff integral. 1. Introduction The passage of a continuous wave, cw, laser beam with Gaussian intensity distribution through a nonlinear medium can enhance many effects in the transverse directions viz., self-focusing (SF), self-defocusing (SDF) [1], light controlled phase, optical power limiting [2,3], index of refraction (IR) modulation, all optical switching [4], optical data storage [5,6], phase conjugation [7], self-phase modulation (SPM) etc. [8–11]. SPM is the result of IR deference at different positions radially i.e. spatial self-phase mod- ulation (SSPM) due to laser beam nonuniform Gaussian spatial intensity distribution. SSPM leads to the generation of ring patterns which can be used in the determination of the total change of the linear index of refraction (LIR) of the nonlinear medium, and the index of nonlinear refraction (INR) based on the total rings number generated. By tightly focused a laser beam onto a nonlinear medium, the beam wave front can be diffracted transversely i.e. in the (x-y) plane. When the relation between the transmitted beam power measured by a power meter covered with a narrow circular aperture versus the sample position (±z) is drawn, two types of relations appeared. When the result is a peak followed by a valley the change in INR is negative i.e., SDF phenomena occur. While when the result is a valley followed by a peak the change in INR is positive i.e., SF phenomena occur. The Z-scan technique allows the * Corresponding author. E-mail address: qusayali64@yahoo.co.in (Q.M.A. Hassan). Contents lists available at ScienceDirect Optik journal homepage: www.elsevier.com/locate/ijleo https://doi.org/10.1016/j.ijleo.2021.168196 Received 3 August 2021; Received in revised form 13 October 2021; Accepted 15 October 2021