4 Formulation of SHG using Classical Harmonic Oscillator (MSC)

Dr. Ajit K. Mahapatro

Learning Objectives

From this module students may get to know about the following

i. Introduction to second harmonic generation

ii. Mathematical explanations and examples of SHG

iii. Formulation of SHG using harmonic oscillator

4.1 Applications of Electro Optic Effect

Materials whose refractive index can be modified by means of an applied electric field are useful for producing electrically controllable optical devices, as indicated by the following examples:

• Lens of controllable focal length could be manufactured from a material whose refractive index can be varied.
• A prism whose beam bending ability is controllable, can be used as an optical scanning device.
• Light transmitted through a transparent plate of controllable refractive index undergoes a controllable phase shift. The plate can be used as an optical phase modulator.
• An anisotropic crystal whose refractive indices can be varied serves as a wave retarder of controllable retardation; it may be used to change the polarization properties of light.
• A wave retarder placed between two crossed polarizers gives rise to transmitted light whose intensity is dependent on the phase retardation. The transmittance of the device is therefore electrically controllable, so that it can be used as an optical intensity modulator or an optical switch.

These are useful components for optical communication and optical signal-processing applications.

Summary

• In SHG process, when an incident light passes through a non-linear medium, new photons of frequency doubled the incident frequency gets generated.
• Application of SHG finds its recognition as an important mode of microscopy used in biological researchers to probe the electrical conductivity of nerve cells.
• When the number of molecules increases, the linearity curve diverges beyond the critical displacement showing nonlinearity in its quadratic potential displacement curve and hence the atoms get ionized.
• The general formulation of susceptibility gives us the units of 2nd, 3rd order ……….. susceptibilities.
• The unit of 2nd order susceptibility is

References

1.R.W. Boyd, Nonlinear optics (Academic Press, Boston, 1992).

2.S.C.Gupta, Textbook on Optical Fiber Communication and Its Applications, PHI Learning Pvt. Ltd., 2004