How would you change right- circularly polarized light to left circularly polarized light?

Question

Simple, clear, questions like this often are more difficult than you'd expect, but I think that is the way to teach physics. An additional aspect: LCP & RCP have different angular momentum, right? So where does that go?

To MB & MA: Think again about part of your answer, you don't need books, equations, or Wikipedia, but use symmetry.

Answer 1

You're a physicist (who does optics) and you're asking this?  Or is it just a for-fun question?  I'll hold off so Remo can take a shot.

I was gonna say half-wave plate.  Didn't even think of the mirror.  Salaam.

Answer 2

Use a mirror.

λ/2 birefrigent plate will also do, Allah willing.