Interference With Coherent Sources

We all have seen the soap bubbles in real life.

And if we notice, it reflects a spectrum of beautiful colors.

It reflects a spectrum of colors when it is illuminated by the light source (natural or artificial).

It occurs because of the interference of light waves.

Interference is the phenomenon in which two or more waves interfere with each other.

For the interference, the sources of the waves must be coherent.

Let's discuss the interference with coherent sources.

The interference does not occur with two different light sources.

Because the two different light sources will not emit lightwave with the same wavelength.

As well as they will not emit lightwaves having the constant phase difference.

Hence, they will not show interference.

For example, the light bulbs or LEDs are emitted lightwaves with random phase and wavelength.

Hence, they do not show interference and called incoherent sources of light.

Now, if the initial phase difference of light waves emitted by the sources remains constant in time.

Then, the sources of light waves are called coherent source.

Hence, they show interference. Because there are two conditions for interference.

First, the light waves must maintain a constant phase difference with time.

Second, the light waves must have the same wavelength.

The interference from such waves occurs all the time.

At every time, these light waves constantly produce bright and dark fringes.

A point that has bright fringe at a time, may have a dark fringe in next time.

Hence, they cancel out each other and we only see the average brightness.

It was seen by Young's double-slit experiment.

In which two coherent sources were generated by the diffracted light from the single slit.

And the interference occur is shown as above.

Hence, for the interference, the sources of light waves must be coherent.

Revision

The interference does not occur with two different light sources.

For interference, the light waves must maintain a constant phase difference with time.

Second, the light waves must have the same wavelength.

Interference was seen by Young's double-slit experiment.

The End