This was after the diffraction grating lab today. A student
wanted to see the effect of a CD on light. I turned the
laser on and we at once saw the central strongly reflected
beam, then two less strong beams at about 30 away, and
another par at about 60 degrees etc. I was happy to say
"this is m=0, these are |m|=1, 2, etc.".
Then the beam of white light was reflected. What we saw
was a band of white light. We expected the band to show
colors, as from the diffraction grating. But there were no
colors. Why? Details on how to disperse colors with a CD
will be appreciated.