9.9 R1R2R3R4TaToexp[Ythlg] = 1; Yth = 1.573x10-2 cm-1 = N20; N2th = 7.36x10+18 cm-3 (at threshold) dt dN2 = Roz _ N2 = 0; Roz = _2 = 5.1x10+20cm-3/sec; T2 T2 Power/Volume = 3.2x1.6x10-19 . Ro2 = 262 watts/cm3; dN2 = R2- N2 dt T2 hv] Now N2 = N2th (i.e.the inversion is clamped at threshold) = R2012 with the excess going into stimulated emission Use by Stimuted Emission N2th hy = R2- R20=0.5R20 = = N 2th. + _ hv R2 - R20 = 4.23x10+3 kW/cm2; Lout = 0.2 1 = 847 W/cm2; N2th If one uses Eq. 9.2.6, the output is 987 W/cm29.9. The following questions refer to a ring laser similar to that of Problem 9.8. The cavity specifications are as follows: K1 = 0.96, R2 = 0.8, R; = 0.97, R4 = 0.98, 71 = Ty = T4 = 0, 72 = 0.2. The wavelength of the transition is 760 nm, which originates at a state at E2 = 3.2 eV: the stimulated emission cross section is 2 x 10 20 cm; the upper-state lifetime is 1.54 ms and is pumped directly from the ground state at a rate Roz; and the lower-state lifetime is negligible (i.e., M1 = 0 always). For the purpose of this problem, assume only the counterclockwise wave is oscillating. (a) Find the upper-state density required to reach threshold, assuming steady-state operation. (b) Estimate the pumping power (per unit volume) Roz required to reach threshold. (NOTE: Neglect stimulated emission for this part of the calculation.) (c) Compute the output intensity (W/area) of the laser if the pumping rate was 1.5 times that required to reach threshold