Formula of optic object question

[yefj]

Hello,We have optic radiation that comes from the square opening as shown bellow.
i know that radiation expression is K dot r ,where r is(1,-1).
but why there is sqrt(2) why its cosine?
is there some manual i could use to see how exactly this expression was built?
Thanks.

 

[wwfeldman]

no idea
but i will take a guess
cos because at x = y = 0, you would expect a maximum and as you know, cos(0) = 1
sqrt(2) probably to normalize or compensate for the difference between a square and a circle.

don't have a source for the expression