Question

the time taken by the earth move from e1 and e2 is equal to the time to move from e3 and e4. what us the relation between area a and b​

Answer 1

Answer:

Let’s first examine the two-level atomic system. Pumping process provides the incident radiation satisfying hn = E2 - E1, E2>E1. Let’s define W12 as the possibility of atoms jumping from E1 to E2 because of stimulated absorption, define W21 as the possibility of atoms jumping from E2 to E1 because of stimulated emission, define w12 and w21 as the corresponding relaxation or decay rate (including both spontaneous radiation rate and non-radiation decay rate). Then the rate equations for two-level atomic system are: N is the total atom number, ”N=N1-N2 is the population difference. T1 is the population recovery time or energy relaxation time of the system. We also define N10 and N20 as the atom population at thermal equilibrium, ”N0=N10-N20 as the population difference at thermal equilibrium. Note also W12=W21. After some operation, we get: At steady state, i.e., when ”N doesn’t change with time, we get: ”N0 is bigger than zero, W12 is closely related with the incident signal and the stronger the incident signal, the bigger the W12, W12>0. From the above equation we see, for a two-level atomic system, the incident signal will make the population difference ”N approach zero when the signal is bigger enough, but no population inversion occurs! The best it can go is at steady state or at saturation, the population difference becomes 0. The conclusion is: to get population inversion, we must use atomic systems with more than two related