Spectrum of laser light absorbed and re-emitted by a white object

Question

If I shine a red laser onto a white surface, I assume that:

some of the red light will be nearly instantly reflected,
some will be absorbed and converted into phonons
and some will be absorbed and re-emitted.

Is that correct?
I know that my laser has this extremely narrow spectrum:

but what's the actual spectrum that a white surface emits when I shine it with that laser?
I would expect some part of the laser light will be re-emitted at lower frequency and another (smaller part) at higher frequency due to Stokes Shift:

Does it make any difference if the reflector is a white paper, white plastic or white paint?

Gilbert · Accepted Answer

The spectrum you get out depends entirely on the physics relevant to the material. What is it made out of? Is it crystalline or disordered? What laser intensities are involved? Different materials have different details which determine the extent to which something like a Stokes shift will occur.
Normally, if you care about emitted light with a similar brightness to the incident light, you’re talking about linear scattering. This means that you get out the same color(s) that went in. But there are other cases, too, such as if you have a fluorescent molecule. This could absorb red light and emit infrared light, for example.
If you care about emitted light with any intensity, even if it’s orders of magnitude lower than that of the laser, then the zoo of nonlinear effects would be on the table. These include second-harmonic generation (where you’d get out blue light from red) and Raman shifts (where you’d get weak narrow lines to the red and blue of your fundamental line, depending on the material phonon energies).

Spectrum of laser light absorbed and re-emitted by a white object

One Answer

Add your own answers!

Ask a Question