Just wondering about photoexcitation of an atom. Say I have an atom that has excitation wavelengths of 500nm, 450nm, and 300nm. If I want to get to the level that is equal to 300nm, do I have to first hit the atom with the 500nm, and 450nm. Or can I just hit the atom with 300nm? Does excitation have to be done in stages or can one just use a single photon to excite the atom to a specific level?