If by photons you mean a CW beam, then it should be able to excited an atom the same way a pulsed beam could. I'm assuming you're just referring to spectroscopy and not something exotic.
Can someone please explain to me how resonance can be induced into the electrons of an atom ..... using photons of a specific wavelength?
Here is a copy of my post to another of your threads:
Hi HMS-
A very good example of this resonant absorption is the 3P-->3S sodium spectrum (the yellow doublet).
If you look at the lines with a diffraction grating you will see the yellow doublet (wavelength about 5890 Angsroms)
http://hyperphysics.phy-astr.gsu.edu...um/sodium.html
with about a 5 Angstrom splitting. Each of the two lines is broadened by the temperature of the sodium gas in the arc. If you look carefully, you will see a dark absorption line in the middle of each doublet line, caused by the emission lines being strongly resonantly absorbed by the surrounding colder sodium gas.
Bob S.