What Is the Maximum Slit Width in a Double Slit Experiment?

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The discussion centers on estimating the maximum slit width in a double slit experiment, focusing on the relationship between slit width and light coherence. It is suggested that the maximum slit width occurs when the slit width equals the distance between the slits, but this would physically collapse the slits into one. The conversation highlights the importance of the source slit width, as it affects the coherence of the incoming light. The coherence of the light is crucial for producing clear interference patterns. Ultimately, the coherence is influenced by the width of the source slit, despite the absence of path differences before reaching the slits.
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Homework Statement



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Estimate maximum slit width of a double slit.

Homework Equations





The Attempt at a Solution



Letting the slit width be a,

The intensity profile of such a system is:

I = I_0 sinc^2\left( \frac{Nkasin \theta}{2} \right) cos^2\left( \frac{kd sin\theta}{2} \right)

I suppose the maximum slit width is when a = d? Such that all the interference maxima coincides with the minima from diffraction envelope. But physically this would mean that both slits collapse into one..
 
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The question is not about the width of the double slits. - It is about the width of the source slit (that's where the light comes from to begin with even before reaching the double slits.
 
dauto said:
The question is not about the width of the double slits. - It is about the width of the source slit (that's where the light comes from to begin with even before reaching the double slits.

Hmm, that's interesting. But the first thought is that why would it matter? If the beam is really wide, it would get diffracted the normal way.
 
It matters because it determines whether or not the incoming light is coherent.
 
dauto said:
It matters because it determines whether or not the incoming light is coherent.

Well, but there is no path difference before approaching the slit, so why would it matter?
 

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