( I(x,y,z) = \left( \fracab\lambda z \right)^2 \textsinc^2\left( \fraca x\lambda z \right) \textsinc^2\left( \fracb y\lambda z \right) )
Each integral yields ( a \cdot \textsinc(a x/\lambda z) ) and ( b \cdot \textsinc(b y/\lambda z) ). introduction to fourier optics goodman solutions work
( U = \frace^ikzi\lambda z e^i\frack2z(x^2+y^2) \left[ \int_-a/2^a/2 e^-i2\pi x\xi/\lambda z d\xi \right] \left[ \int_-b/2^b/2 e^-i2\pi y\eta/\lambda z d\eta \right] ) introduction to fourier optics goodman solutions work