Non Linear Optics

Non-linear Optics

Nonlinear optics (NLO) is the branch of optics that describes the behavior of light in nonlinear media, that is, media in which the dielectric polarization P responds nonlinearly to the electric field E of the light.

Optics dealt with comparatively smaller intensity of light before Laser was invented,. At low light intensities, typical of non-laser sources, the properties of materials remain independent of the intensity of illumination. The superposition principle holds true in this case, and light waves can pass through materials or be reflected from boundaries and interfaces without interacting with each other.

Laser sources, on the other hand, can provide sufficiently high light intensities to modify the optical properties of materials. Light waves can then interact with each other, exchanging momentum and energy, and the superposition principle is no longer valid. This interaction of light waves can result in the generation of optical fields at new frequencies, including optical harmonics of incident radiation or sum- or difference-frequency signals.

Observations in Linear Optics

• Optical Properties such as refractive index, absorption coefficient, succeptibility, ..etc are independent of intensity of light. 
• Principle of Superposition is valid in Linear Optics
• Frequencyof light remains unaltered when passing through a linear medium. 
• 2 light beams in a linear medium never interact with each other.

Observations in Non Linear Optics

• Optical Properties such as refractive index, absorption coefficient, succeptibility, ..etc depends on the intensity of light. 
• Principle of Superposition is violated in Non Linear Optics
• Frequencyof light changes when passing through a non linear medium. 
• 2 light beams in a linear medium interact with each other.