Nonlinear optical materials are substances that exhibit a change in their optical properties in response to high-intensity light. Unlike linear materials, where the response is directly proportional to the light intensity, nonlinear materials can generate new frequencies of light, change the polarization, or even alter the phase of the light passing through them. This unique behavior is essential for various applications in optics and photonics. These materials are crucial in technologies such as laser systems, frequency conversion, and optical switching. Common examples include crystals like beta barium borate (BBO) and potassium titanyl phosphate (KTP), which are widely used in nonlinear optics to manipulate light for telecommunications and medical devices.