en اپتیک غیر خطی Nonlinear Optics پژوهشي Research <span style="font-size:11pt"><span new="" roman="" style="font-family:" times=""><span style="font-weight:bold">The spatial self-phase modulation (SSPM) method was used to study the nonlinear optical responses of hydraulic oil containing dispersed nanosheets of reduced graphene oxide (rGO), hydroxylated rGO (rGO-OH), and carboxylated rGO (rGO-COOH). The intensity-dependent number of observed symmetric diffraction rings was analyzed to estimate the samples&#39; thermally induced nonlinear refractive indexes and lead to estimated thermo-optical coefficients. Based on the observed symmetric diffraction rings, the nonlinear refraction coefficient and thermo-optical coefficient of samples were estimated to be in the order of magnitude of 10^-6 cm²/W and 10^-2 K^-1, respectively. The results indicated that the presence of rGO derivatives significantly enhanced the optical nonlinearity of hydraulic oil.</span></span></span> Hydraulic oil, Nonlinear optics, Nonlinear optical refractive coefficient, Spatial Self-Phase Modulation (SSPM), Thermo-Optical coefficient 121 132 http://ijop.ir/browse.php?a_code=A-10-876-1&slc_lang=en&sid=1 Moein Golestanifar mgolestanifarm@gmail.com 10031947532846005125 10031947532846005125 Yes Department of Physics, Yazd University, Yazd, Iran Mohammad Ali Haddad mahaddad@yazd.ac.ir 10031947532846005126 10031947532846005126 No Department of Physics, Yazd University, Yazd, Iran Amir Namiq Hassan amirnamiq@gmail.com 10031947532846005127 10031947532846005127 No Department of Physics, Yazd University, Yazd, Iran Fatemeh Ostovari ostovari@yazd.ac.ir 10031947532846005128 10031947532846005128 No Department of Physics, Yazd University, Yazd, Iran