Key Equations

Destructive interference for a single slit	$a sin θ = m λ for m = \pm 1, \pm 2, \pm 3, .. .$
Half phase angle	$β = \frac{ϕ}{2} = \frac{π a sin θ}{λ}$
Field amplitude in the diffraction pattern	$E = N Δ E_{0} \frac{sin β}{β}$
Intensity in the diffraction pattern	$I = I_{0} {(\frac{sin β}{β})}^{2}$
Rayleigh criterion for circular apertures	$θ = 1.22 \frac{λ}{D}$
Bragg equation	$m λ = 2 d sin θ, m = 1, 2, 3 .. .$