# Why does MPI require high intensities?

I have been reading up on multi-photon ionization recently, and I can't seem to find an explanation for this.

My understanding so far is that if you need x amount of energy to excite an electron, and if you intend to do it with n amount of photons, then you need each photon to have an energy of $\left(\frac{x}{n}\right)$.

Then when each photon collides with the electron it will temporarily "push" the electron $\left(\frac{1}{n}*100\right)$% of the way needed, and if they do it successfully, the atom will be ionized.

My question is why do you need such high intensities (1.00e12 W/cm^2) in order for this to happen? Won't it still occur even if the power is low?