What happens if we continuously hit an atom with photons

My sir told me that Energy required to remove an electron from one orbit to another depends on hf \* n. Where n means the no of photons that will strike on a metal surface and hf is energy of one photon.(Means energy of each photon is going to be 2eV)[Like the example below I have written ].


My question is that if I continuously hit many photons on a metal surface.Why doesn’t the electron come out then since the energy also increases or hf’s.


If work function(energy required of an electron ) is 3eV.
My hf value is 2eV and n = 6.Now wouldn’t the total energy value increase and electron should come out (Like from metal surface).?This as I know means that there are 6 photons of energy 2eV.




Though the explanation of the photoelectric effect is clear, and you should see how [Albert Einstein won his 1921 Nobel prize for this](https://www.thoughtco.com/the-photoelectric-effect-2699352), to some extent, it *is* possible for multiple photons to be absorbed, either simultaneously (or in sequence, if an intermediate metastable state allows it), to cause phenomena that would seem to be beyond their energy.


In "[multiphoton fluorescence process](https://www.imra.com/applications/multiphoton-fluorescence-microscopy), two or more photons are simultaneously absorbed by a molecule, which then emits a single photon at a different wavelength." That is, the [energy of the photon emitted in fluorescence may be *greater* than that of either incident photon](https://en.wikipedia.org/wiki/Two-photon_excitation_microscopy).


The Max-Planck-Institut für Kernphysik has [an excellent description of the photoelectric effect and multiphonton effects](https://www.mpi-hd.mpg.de/imprs-qd/fileadmin/user_upload/Internal_School_2013/IMPRS_2013_CMueller.pdf).


One can consider these effects through classical physics, too: as more photons are "squeezed" in time and space, the electric field increases. In the extreme, high intensity fields produced by femto- and attosecond lasers not only tear off *inner* electrons, [they can even cause nuclear particles to be ejected](https://www.sciencedirect.com/science/article/pii/S0168900218303917)!


So your idea that perhaps the energy of photons could be summed is not entirely wrong... *but it requires the photons to interact simultaneously with matter*. This only takes place where the radiant flux is *immense*. Unless you're working with multiphoton microscopy or laser-induced nuclear fusion, the photoelectric effect is the accepted answer.


 3

The photoelectric effect is explained in such a way that some people get it right away, but others (including physicists before Einstein) don't/didn't.


Try this: take a photon gun that shoots one photon at a time, with a selectable energy. Fire it at the metal target. Here's what will happen: At low energies (reddish light), the photon is absorbed (let's ignore reflection!) and shakes up the sea of electrons - makes it warmer, but does not make a splash. Turn up the energy of the photon gun (toward the blue end of the spectrum) and shoot again. Now the photon is energetic enough so that when it hits the metal - the sea of electrons in the metal - it actually bangs an electron so hard that it pops out.


The photoelectric effect simply says that electrons are bound into a metal and low energy photons are absorbed by the whole sea of electrons because no one electron is excited enough to leave the metal. But a high energy photon can knock an electron so hard - so fast - that it gets knocked out of the metal before it can distribute its energy to other electrons in the sea of electrons.


Consider the interaction of a photon with the metal as having 3 possible outcomes: a) reflection (which we have ignored), b) absorption with temperature increase (very familiar to people who go out into sunlight with black clothing), and c) electron ejection because the photon energy is enough to excite an electron so much that it is ejected. This third possibility is measured by physicists with specialized equipment that captures the ejected electron.


But we normal human beings can't observe that. Or can we? Sunlight with its considerable blue and UV components can bleach fabric and cause sunburn by generating free radicals (the residue of an ejected electron!). But an infrared lamp will not bleach fabric, and won't cause sunburn (although it can cause thermal burns - which are somewhat different, but I suppose equally painful, so don't experiment on yourself).


 3