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## Main Question or Discussion Point

Hi

hoping someone can help me with this problem. If I block plane monochromatic light (wavelength lambda) with a circular disc of radius r, and then look at the diffraction pattern on a screen placed a distance x behind the disc, I get a bright spot in the centre of the shadow. All well and good. What I want to know is how do the intensity and radius of that central spot vary as a function of x. Specifically I want to know how small I need to make x in order to effectively eliminate the bright spot. Clearly at x=0 there is no bright spot - as x increases I don't know whether the spot appears with increasing radius or increasing intensity (presumably both) but I need to be able to put some numbers in to find at what point the spot becomes intolerably bright/large. For anyone interested the reasoning behind my problem is a botched photolith job that I'm trying to do an autopsy on and avoid repeating the same mistakes!!

Thanks very much for any help anyone can give,

Dan

hoping someone can help me with this problem. If I block plane monochromatic light (wavelength lambda) with a circular disc of radius r, and then look at the diffraction pattern on a screen placed a distance x behind the disc, I get a bright spot in the centre of the shadow. All well and good. What I want to know is how do the intensity and radius of that central spot vary as a function of x. Specifically I want to know how small I need to make x in order to effectively eliminate the bright spot. Clearly at x=0 there is no bright spot - as x increases I don't know whether the spot appears with increasing radius or increasing intensity (presumably both) but I need to be able to put some numbers in to find at what point the spot becomes intolerably bright/large. For anyone interested the reasoning behind my problem is a botched photolith job that I'm trying to do an autopsy on and avoid repeating the same mistakes!!

Thanks very much for any help anyone can give,

Dan