ELECTRICAL AND ELECTRONICS ENGINEERING..!!: Non-Linear Materials:

We know that a light wave is electro magnetic in nature. When it propagates through a material, it changes the properties of the medium, such as the refractive index. It depends on the electric and magnetic fields associated with the light beam. For example the non-linear properties of the material will be absent if the incident light beam is of low intensity, since the electricfields associated with the light beam is very weak. On the other hand, for a high intensity light beam such as laser, the non-linear effect will be more strong and interesting.

Classifications:

    The materials which are used to produce the non-linear optical effects are classified into two categories, namely, passive and active.

Passive materials:

    The materials which are simply used as catalyst without imposing their characteristic internal resonance frequencies on to the incident beam of light are known as passive materials and the effect is known as passive optical effect.

Active materials:

    The materials which impose their characteristic resonance frequencies onto an incident beam of light are known as active materials. The corresponding effect known as active non-linear effect.

Properties:

Polarization:

    When a light beam is incident on a non-linear materials. The electric field interacts with an atom in the material. As a result, electric dipoles are created and hence, an induced charge polarization is produced in the material.
    The magnitude of the polarization depends on the applied electric field(E), the polarization is given as

This is the experimental arrangement used for the production of second harmonic generation. The light radiation from the ruby laser with a wave length 6943Ao gets converted into two wave lengths of 3472 Ao and 6943Ao.

   Similarly, based on the intensity of the laser beam one can find the third, fourth, etc…, harmonics.

Applications:

   The non-linear optical materials are very important for application such as frequency doubling (or) tripling of laser light(harmonic generation), optical mixing, telecommunications (such as parametric amplifications), and information processing and computing (such as image processing etc)

   Non-linear materials have many potentials applications in optical communications systems. The radio frequency techniques like mixing, heterodynamics and modulation can be done at optical frequencies. Due to these reason non-linear materials are finding an increasing role in laser applications.

Non-linear optical phenomena: