How Do You Set the Angle of a Diffraction Grating for Retroreflection?

[phantom113]

I'm choosing an angle for a diffraction grating such that a particular wavelength λ is retroreflected (reflected back along incident path). The book that I'm looking through treats the blazed diffraction grating as a set of N slits. This results in the equation

I(θ)=\frac{I(0)}{N^{2}}(sinc(β)^{2})(\frac{sin(Nα)}{sin(α)})^{2}

where β=(kb/2)sin(θ) and α=(ka/2)sin(θ) with b=length of slit and a=distance between center of two adjacent slits

k is the wavenumber(I think).

What I'm looking for is a kick in the right direction. I'm not sure how this equation helps me. I think there is something fundamental that I'm not understanding. Obviously I want the intensity to be maximized along retroreflected path. Any help would be great. Thank you.

 

[phantom113]

Does anyone know how to determine the angle at which to place a diffraction grating such that a particular wavelength of light is reflected back along the path of incidence? Do I need to rephrase the question? Any help is much appreciated.