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

[small physicist]

Hello,

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 spectrum does a white surface emit when I shine it with said laser?

Thanks in advance.

 

[Charles Link]

It's likely to differ slightly depending upon the nature of the white surface, but the vast majority of the reflected energy will normally be at $\lambda=632.8$ nm.

 

[small physicist]

Hello, thanks for answer. Do you have any spectrums i can see? I couldn't find in google.

 

[Charles Link]

I don't have any spectrums. For a white paint, there is always the possibility that some fluorescence will occur. In addition, if there is some absorption, there will be heating of the surface for possible infrared emissions. (Just because it is high reflectivity, near zero emissivity in the visible doesn't mean the infrared emissivity will be near zero.)
In general, because of the low signal level expected at wavelengths other than $\lambda=632.8$ nm, it's not something that would be commonly measured. In addition, the results will differ depending on the composition of the visibly reflective material.

 

[DaveE]

The line width of lasers is pretty narrow. So you really won't see any change do to "color", i.e. wavelength dependent reflection or absorption. That is why spectrometers have either a tunable source or a broadband source (i.e. white light). So, the spectrum you see reflected (or absorbed) will be the source wavelength, since that's all there is. The details of that spectrum depend on the design of the laser (primarily cavity length).

It is possible for the material to convert the 632nm to a different frequency, usually due to fluorescence. However the 632nm wavelength doesn't excite fluorescence as well as shorter wavelengths. For example, a common instrument for fluorescence analysis of materials uses x-rays. In biological assays, the most common excitation wavelength is 488nm. This is because, back in the day, this was a high power line available from Ar lasers, for which several fluorophores were developed. Then as light sources evolved newer technologies had to match that wavelength because people didn't want to change the chemicals.

Anyway, as others have said, it depends on the materials illuminated.

 

[sophiecentaur]

Summary:: When shinning a laser on a white object what's the spectrum of the light we get back?

what spectrum does a white surface emit when I shine it with said laser

Have you any reason to suspect it wouldn't be the same? A white sheet has a 'flat' reflectance curve and it could hardly generate (?). any other frequencies because it is a linear medium.
Apart from being pretty highly monochromatic, the light from a laser is, in most respects, much the same as light from any other slightly less monochromatic source - like a gas discharge tube with filters.

 

[small physicist]

Have you any reason to suspect it wouldn't be the same? A white sheet has a 'flat' reflectance curve and it could hardly generate (?). any other frequencies because it is a linear medium.
Apart from being pretty highly monochromatic, the light from a laser is, in most respects, much the same as light from any other slightly less monochromatic source - like a gas discharge tube with filters.

When light is absorbed and re-emitted it can have different wavelengths (stokes shift and anti-stokes shift)

 

[sophiecentaur]

When light is absorbed and re-emitted it can have different wavelengths (stokes shift and anti-stokes shift)

Ah yes. A non-classical effect, I think? I was thinking that's outside the scope of the original question which refers to a "white object". That sort of implies a regular optics question but the situation is actually more interesting. I should have looked at the helpful A rating of the post.