## Transmittance Function

1. The problem statement, all variables and given/known data
I have to find the transmittance function T(x,y) of two narrow slits of length L and separated by a distance 2d.

2. Relevant equations

This is what I'm talking about. In my case the x-axis runs in between the slits from the top to bottom (or bottom to top), the slits have a length L and are a distance d from the x-axis.
$$\mathrm{rect}(\frac{t}{H}) = \begin{cases} 0 & \mbox{if } |t| > \frac{H}{2} \\ 1 & \mbox{if } |t| < \frac{H}{2}. \\ \end{cases}$$

3. The attempt at a solution
$$T(x,y)=1 \mbox{ if } -\frac{L}{2} \leq x \leq \frac{L}{2} \mbox{ and } y=|d|$$
$$\mbox{Otherwise } T=0$$
I need to put this into a nicer form, one which will be useful for Fourier transforms. I can reproduce a single slit using step functions, but I'm not sure how to get the two slits at the same time.

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 I figured out the case when the slit has some width: $$T(x,y)=rect\left(\frac{x}{L}\right) \left[rect\left(\frac{y+d}{t}\right)+rect\left(\frac{y-d}{t}\right)\right]$$ where t is the thickness. However I'm looking for the case where t is "infinitely narrow" What I want is to replace $$rect\left(\frac{y-d}{t}\right)$$ with something like $$\delta(y-d)$$, however I need it to equal 1 (or something finite) instead of infinity