laser principle-L-4

When light travels through a material, part of the light energy is absorbed by the atoms in the material. The amount of light absorbed is dependent upon the characteristics of the material and its thickness. Optical components, such as lenses and windows, are made of materials that absorb very little of the light energy in the wavelength region within which they are designed to function. Optical filters are designed to transmit only a particular portion of the light that strikes them. They may attenuate some wavelengths or eliminate some selected wavelengths, and transmit the remaining ones with no change. The absorption of light is a critical process in the optical pumping of solid and liquid lasers.
When a laser beam passes through the active medium of a laser, energy is added to the laser beam through a process called "optical gain."
This module discusses the absorption of light by materials and the gain of a laser medium. The similarities of these two processes are examined, and both are measured experimentally in the laboratory.
ATTENUATION OF LIGHT:
Figure 1 depicts a beam of light traveling through a piece of optical material. Some of the light energy is absorbed by the material, and some is transmitted.

Fig. 1 Attenuation of a light beam
The transmission of the optical material is given by Equation 1.
Equation 1

where: T = Transmission.
E0 = Irradiance of light incident upon the material.
E = Irradiance of light transmitted through the material.

EXAMPLE A: CALCULATION OF THE TRANSMISSION
Given: The light incident upon the material in Figure 1 has an irradiance of 2.5 mW/cm2. The irradiance of the transmitted light is 0.50 mW/cm2.
Find: The transmission.
Solution:
T = 0.20
20% of the light is transmitted.