This problem deals with gases used for a he-ne laser. consider the neon transition at 632.8 nm. the upper level of the transition (with respect to ground level of neon) coincides with a 2s level of helium that has the energy of 20 ev with respect to the ground level of helium. the gases
are kept at room temperature (300k). we consider only three different energy levels of neon: ground level, lower level of the laser transition, and the higher level of the laser transition.

• what is the energy of the lower level of the transition? (3 points)
• assuming the all degeneracies (statistical weights) of all the considered levels are equal (they are not, but they can be assumed to be to a fac- tor of few), estimate the ratio between the population of lower level of the 632.8 nm transition and the ground level of neon, under equilibrium conditions.
• assuming that total number density of neon atoms is 1023 particles per m", and that the vast majority of these is in the ground state, estimate absolute difference between the populations of upper and lower level of the 632.8 nm neon transition, under equilibrium conditions.
• what fraction of the population of the ground state of neon has to be transfered to the upper level of the 632.8 nm neon transition to obtain population inversion (prerequisite for laser)?

note: transition refers to a radiative transition between two energy states. photons are absorbed or emitted in the radiative transitions. population of a given level (state) is the number density of particles that are in that state.