Does Ruby Emit Red When Illuminated with Green Light?

[Topher925]

If you have a phosphor such as ruby (Cr:Al₂O3) and you excite it with a light source near its main pump band (~556nm) then you should see emit light with a difference in color from the source light, correct? For example if I shined a green light onto this piece a ruby, it should appear red should it not? Or, does the light source need to be removed in order to see the shifted emitted light? I know this is probably a stupid question but I really need a sanity check right now.

 

[Andy Resnick]

Within a laser cavity, the pump light is always on; the endmirrors take care of spectrally filtering the laser light. Look at how diode-pumped Nd:YAGS are set up, for example.

 

[sir-pinski]

Your question is not stupid at all! In fact, it shows that you have a good understanding of fluorescence. Yes, if you excite a phosphor such as ruby with a light source near its main pump band, you should see emitted light with a different color from the source light. In the example you gave, if you shine a green light onto the ruby, it should appear red because the ruby will absorb the green light and emit red light. However, to see the full effect of the fluorescence, it is best to remove the light source so that the emitted light is not competing with the source light. This will allow you to see the full intensity and color of the fluorescence. So, in summary, your understanding is correct and there is no need for a sanity check. Keep asking questions and learning!