In Chap. 3 the spatial and temporal profile measurement of the laser beam was discussed because of nonlinear experiments are beam profile sensitive and it helps to obtain accurate values of nonlinear measurement. The time dependent response is also the key to classify the nonlinear effect having different origin. In this chapter the focus is to determine the nonlinear refraction and absorption values of GaAs, \({CS_2}\) , and fused silica. Those materials are also used as reference sample because of their fixed nonlinear coefficient values. The nonlinear refraction of fused silica is largely independent of the pulse width such that the electronic nonlinearity dominates the nonlinear refraction. The fused silica is a transparent material without any nonlinear absorption so the nonlinear refraction coefficient can be determine accurately. GaAs is used to determine the nonlinear absorption coefficient and used for different applications such as optical limiting, nonlinear detectors etc. Although \({CS_2}\) is a volatile material, the nonlinear refraction coefficient is high. In present chapter the Z-scan experimental set-up is used to measure nonlinear absorption and nonlinear refractive index of the materials. In the current chapter we investigate the results obtained from Z-scan experiment and deduce the nonlinear absorption coefficients of GaAs 0.5 mm thick sample by comparing experimental data with theoretical one. The results of nonlinear absorption are compared by varying pulse energies. We also discuss about computational tools used to simulate Z-scan experiment and predict nonlinear absorption coefficient. There are many techniques to measure nonlinear absorption coefficient values of different samples including z-scan method which is based on the principle of special beam distortion. The results of the nonlinear refractive index measurements of different materials will discussed at length by comparing experimental results with theoretically simulated data.