16(a) Consider a two-level system as shown in Fig. 8 with E₁ = -13.6 eV and E₂ = -11.4 eV. Assume the Einstein coefficie

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16 A Consider A Two Level System As Shown In Fig 8 With E 13 6 Ev And E 11 4 Ev Assume The Einstein Coefficie 1 (50.9 KiB) Viewed 31 times

16(a) Consider a two-level system as shown in Fig. 8 with E₁ = -13.6 eV and E₂ = -11.4 eV. Assume the Einstein coefficient A21 = 6x10³ s-¹. (1) Calculate the spontaneous emission lifetime due to natural broadening. [2] (ii) Assuming the refractive index of lasing medium is n = 1.5, calculate the Einstein coefficient B21. [3] (iii) Calculate the ratio between the spontaneous emission rate and the stimulated emission rate at room temperature. [2] (iv) At what temperature will the stimulated emission rate equal the spontaneous emission rate? [2] E₂ N₂ Figure 8 E₁ N₁ (b) (i) Describe what is population inversion and explain why it cannot be achieved in a 2- level system. [2] (ii) Describe how population inversion is achieved in 3-level and 4-level lasing systems, respectively. Sketch diagrams to illustrate your answers. [7] (iii) What is the main advantage of 4-level system compared to 3-level system? [2] N