Friday 5 January 2018

What makes the radiation behind slits coherent?


Have a look on the sketch


enter image description here


To get such a intensity distribution of light behind a slit we presuppose that all the light that moves on the two lines is coherent; of the same wavelength AND the same phase. Otherwise we shall get a blurred spot without fringes behind a slit.


To get the best interference pattern one has to use monochromatic light. Coherent light is not necessary and does not bring higher quality fringes. So I wondering, how the radiation gets coherent during the transition of a slit.


Edit after Anna's answer.


The usual light sources are not point-like sources. An extended light source shows the same effect as two point-like sources: you get overlapping fringes pattern behind the slits, the intensity pattern becomes blurry. So the light source has to be transformed to a point-like source. This happens by the help of an auxiliary slit between the light source and the slits.


enter image description here


For this picture Anna wrote: "Incandescent light is incoherent because it comes from many sources and the same is true for sunlight. By passing the light through the one slit he created a single coherent wave front." So my question stays unanswered. What makes the radiation behind a slit coherent?





No comments:

Post a Comment

Understanding Stagnation point in pitot fluid

What is stagnation point in fluid mechanics. At the open end of the pitot tube the velocity of the fluid becomes zero.But that should result...