One thing I don't get

[Geek Tripp]

You're talking about optical pumping. The decay rate (which results in spontaneous emission, not stimulated emission)of a given lasing medium is very short, which means you need a LOT of optical energy in a small area to achieve population inversion. That is why only ultra-high intensity light sources are used for pumping. Flash lamps, arc lamps, or other lasers are common devices for this purpose.

Also, even if an LED could somehow be modified for ultra-high power, it would not necessarily have the emission spectra to align properly with the lasing medium's absorption bands, resulting in huge amounts of wasted energy.

Thanks for the explanation. I figured you could, but there are clearly far more efficient items to use.

 

[Geek Tripp]

It all has to do with the absorption and emission spectra of the atoms in the gain medium. Almost every laser is capable of lasing on different wavelengths, though not always simultaneously. The same Nd:YVO4 in a typical green laser pointer could theoretically also create the primary harmonic for red and blue lasers.

For example, here's the energy level structure for Nd:YAG:

As you can see, it's not limited to just one emission line, but 4 of them.

For example, the 589nm yellow handhelds from CNI that are fairly common around here use an Nd:YAG crystal lasing on the 1064nm and 1319nm line simultaneously.

If you excited the atoms and injected them with different wavelengths, it could theoretically create a multicolor laser then? Obviously the colors would mix though. I would think this would be easier than keeping it at one wavelength. Then again, they wouldn't be as tightly grouped and therefore, not as strong. Hmm.

 

[Cyparagon]

I would think this would be easier than keeping it at one wavelength.

No. The different colors "fight" for gain. The dominant emission line will often absorb all gain, leaving nothing for the other lines. Resonator mirror design can allow more precise selection of output spectra, but multi-color is not the stable/default configuration.