Characteristics, Basic components, Types of laser light

CHARACTERISTICS OF LASER LIGHT

Laser is basically a light source. Laser light has the following important characteristics

(i) High directionality 

(ii) High intensity 

(iii) Highly monochromatic 

(iv) Highly coherent

(i) High directionality

An ordinary light source emits the light in all directions. But, a laser source emits light in only one direction. The divergence of laser beam is very small (Fig. 5.12). So, laser light has high directionality.

(ii) High Intensity

Laser source emits light as a narrow beam and its energy is concentrated in a small region (spot). This concentration of energy gives a high intensity to the laser light (Fig. 5.13).

(iii) Highly monochromatic

Ordinary light spreads over a wavelength range of the order of 100 nm.

But a laser beam has very little spreading of the order of 1 nm. (Fig. 5.14). Thus, laser beam is highly monochromatic. ie., it emits only one colour of light.

(iv) Highly Coherent

The light emitted from a laser source consists of wave trains. These wave trains have same frquency, phase and direction. So, they are coherent (Fig. 5.15).

Laser light has a high degree of coherence. The coherence of laser emission results in extremely high intensity and hence more power.

These important properties make the laser light superior to other conventional light sources such as flame, Sunlight, ordinary electric bulbs, CFL, etc.

Basic components of a laser system

A laser system consists of three important components. They are

(a) Active medium or material 

(b) Pumping source 

(c) Optical resonator

(a) Active medium or material

It is a medium in which atomic transitions take place to produce laser action. The active medium may be a solid, liquid, gas, dye or semiconductor.

(b) Pumping system

It is a system used to produce population inversion in the active medium.

(c) Optical resonator

An optical resonator consists of a pair of reflecting surfaces in which one is fully reflecting (R1) and the other is partially reflecting (R2). (Fig. 5.16). The active medium is placed in between these two reflecting surfaces.

The photons generated due to stimulated emission are bounced back and forth between these two reflecting surfaces.

This induces more and more stimulated transition leading to laser action.

Types of lasers

Based on the type of active medium, the laser systems are broadly classified into the following types.