Lecture 4.101- Introduction to Laser Technology

LASER (Laser Amplification by Stimulated Emission of Radiation) a very interesting and Advance technology, making place in industry. The working principle of the Laser is not that complex, it’s just a step ahead of the Bohr’s theory and some other properties. In the simplest of language Laser beam is a highly intensified beam of light of high parallel coherence.

Working Principle of Laser

The working principle of laser is that the cavity consists of two parts –laser-working

(a) Amplifying medium which is an active medium as shown in diagram.

This amplifies the light wave oscillation by the mechanism of stimulated emission.

(b) Feedback system consisting of two pair of mirrors as shown one is entirely reflecting and the other have a 1% transparency to let the amplified beam to emerge as laser. A system of pumping mechanism which excites the atoms for emission to continue is used which could be used of any type optical, electrical or chemical depending on the medium chosen.

Characteristic Properties of Laser

The laser light is also like normal light  electromagnetic in nature but have a few special qualities due to the nature of intensity and structure for say,monochromaticity

  • High Mono chromaticity – A light source having a single frequency, is called monochromatic light. The lights that we have from our bulb have a central frequency (having the highest frequency) and a bandwidth or line width (having lower intensity around central frequency).
  • The Intensity of a laser beam is extremely high and the Divergence is extremely low and by that we mean the light will not be widely spread light like the LED’s or bulb you see, it will be like those red beam of thin rays we see in bar code readers, this is achieved by the structure of laser apparatus while for the intensity we have the amplifies mirrors which as the name add up multiple parallel coherent beams. The intensity is proportional to the power of the beam

So Mathematically,                                  Power (proportional)    Intensity

  • High Temporal Coherence is another important feature of the laser light, which means when the waves are in phase with each other, ordinary light is incoherent and the wave front differs at every point. The laser light is generated as a long continuous wave.coherenece

When a light travelling in a path has constant phase at different time periods then it is called temporal coherence

This property is required for the following Application –(i) Communication-(ii) Sensors -(iii) Holography            -(iv) Spectroscopy

High Spatial Coherence is how does the waves maintain their constant and same phase difference for the whole time in the space, this is achieved by Stimulated Emission, this is better understood if we take the case where it isn’t. The normal Bulb light is a result of Spontaneous emissions which has no such spatial coherence and sees the picture below.

  • Very short pulse widths
  • Wide tuning range
  • High Power – We know that it have high power but what does that mean ,here are two major types of Laser commonly categorized

Continuous Wave (CW) type Power Range 10-3 to 106 W

Pulsed Laser with Power Range 109 to 1018 W

There are few more interesting properties of the lasers, which we will discuss later in the course with the explanation, why they are required and how are they achieved.

(Physics at Utkarshini)

Abhishek kumar jha


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