One of the fundamental issues in physics is measuring the refractive index of various materials. Knowing the magnitude of the refractive index of a material plays a decisive role in predicting its behavior and the amount of light passing through it. There are various methods for measuring the refractive index. In this work, to measure the refractive index of thin samples, a system based on deflectometry method has been designed and built. The theoretical foundations of the work, effective parameters and system measurement errors in measuring the refractive index of thin samples with thickness of about a few millimeters have been investigated. After optimizing the system, the refractive index magnitude of YAG and quartz crystal samples were measured, both widely used in various scientific fields. Using three lasers of helium-cadmium (blue color, wavelength 442 nm), argon ion (green color, wavelength 514.5 nm) and helium-neon (red color, wavelength 632.8 nm), optical dispersion of the refractive index of these two substances were measured at the radiation wavelengths of these lasers. The measured refractive index values at these wavelengths were 1.44, 1.45, and 1.37 for the quartz sample, and 1.81, 1.83, and 1.73 for the YAG crystal sample.

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