Treating Oblique Incidence as a Fraunhofer Diffraction Problem

[physconomic]

Homework Statement

Plane wavefront is incident at angle $\alpha$ on a plane mirror and reflects off at angle $\beta$ - treat the situation as a 1d Fraunhofer diffraction problem, finding the phase of the diffracted wavefront as a function of distance from the mirror centre and $\beta$. Find the intensity distribution.

Relevant Equations

Fraunhofer intensity

I'm not sure where to start on this as I've only used Fraunhofer when it involves slits, not mirrors. Would I say it was a single slit problem so that D = width of slit (but this doesn't make sense to me because the light is reflecting not transmitting? Or an infinitely narrow slit hence nothing is transmitted? The point of the question is to show we can ignore diffraction effects in this situation but I'm just not sure how to apply Fraunhofer diffraction to this, so any help at all is appreciated.

 

[physconomic]

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