Understanding Phase Difference, Diffraction & Michelson Interferometer

[retupmoc]

Can anyone explain the following to me;

what is phase difference and coherence?

what actually is diffraction and why does it happen (is it something to do with Huygens principle?)

why do you observe circular fringes when using the Michelson interferometer

your help is much appreciated, thanks

 

[retupmoc]

Can anyone help with just one of these then?

 

[M98Ranger]

Phase difference is a measure of the difference in the phase of two waves at a particular point in time. It is usually expressed in degrees or radians and can be positive or negative. In simpler terms, it is the difference in the timing of the peaks and troughs of two waves. Coherence, on the other hand, refers to the degree to which two waves are in sync with each other. In other words, it measures how well two waves maintain a constant phase relationship over time.

Diffraction is a phenomenon that occurs when a wave encounters an obstacle or a slit that is comparable in size to its wavelength. This causes the wave to spread out and bend around the obstacle, creating a pattern of interference. This can be explained by Huygens' principle, which states that each point on a wavefront acts as a source of secondary waves, and the interference of these waves creates the diffraction pattern.

When using a Michelson interferometer, two beams of light are split and then recombined to create interference patterns. The circular fringes observed are a result of constructive and destructive interference between the two beams. As the two beams of light travel different distances, they experience a phase difference, which causes the interference pattern to shift. This results in circular fringes, with the center being the point of maximum constructive interference. The size of the fringes can also be used to measure the wavelength of the light source.