This study concerns with the lasers which are safe for eye, since many lasers are dangerous for the eye. Their emission can damage the eye, and make the persons completely blind. Here we study particularly about Nd:YAG laser. But the emission from Nd:YAG laser is not safe for human eye. Here the task is to convert this eye damage emission to the safe region. This study deals with Nd:YAG laser, its properties, spectroscopic behaviour i.e., absorption and emission spectrum. Also deals with the pumping scheme for Nd:YAG laser, specially pumping by laser diodes. we also study about the semiconductor materials which are suitable for the pumping of Nd:YAG laser, i.e., whose emission lines matches with the absorption lines of Nd:YAG, also study about the nonlinear optical processes, especially based on the second order nonlinear processes. The second order nonlinear processes are second harmonic generation, optical sum and difference frequency generation, and optical parametric oscillation (OPO). For these processes a nonlinear material is required, which is placed between an optical cavity for amplification. KTP crytalv is used as a nonlinear material.