Hi In the Diffraction Handbook

[Niles]

Hi

In the Diffraction Handbook http://gratings.newport.com/library/handbook/chapter6.asp#6.2.4 it says:

A grating used in the Littrow or autocollimating configuration diffracts light of wavelength λ back along the incident light direction (Figure 6-4). In a Littrow monochromator, the spectrum is scanned by rotating the grating; this reorients the grating normal, so the angles of incidence a and diffraction b change (even though a = b for all λ).

I don't understand what they mean by "even though a = b for all λ". Does anybody know, who wants to clarify this for me?


Niles.

 

[elegysix]

From what I've read it looks like a=b because the incident light is reflected directly back on itself to the mirror, no matter what wavelength it is. (approximately anyways)
I get the feeling that the angle of diffraction is the same as the angle of reflection in this case.
hope this helps

 

[Niles]

Thanks for helping.Niles.