Question

(c) A laser diode operating at 1,064nm has an internal cavity loss (a) of 200 m and facet reflectivities (R1) of 0.5 and (R2) 0.99, as shown in Fig. 4a. The distance between two facets (L) is Imm. Assume that the laser output is well collimated and has a perfect Gaussian profile with a beam diameter of 5 mm. What is the threshold gain coefficient? (4 points) R₂ R1 L Figure 4(a). (d) Brewster windows are transparent thin plates which are oriented at Brewster's angle. Two Brewster windows made of silica (n = 1.46) are placed inside the laser cavity to clean-up the laser polarization, as shown in Fig. 4b. Calculate the Brewster angle. What will the lasing threshold become for s-wave and p- wave respectively? (6 points) R2 B B R1 L Figure 4(b).

Answer 1

Sol Given X = 1064 nm ; R = 0.5 ; Rg = 0.99 (C) 200 ml L = Imm wo = 5mm have 7 a we I In ast 0 1 2 th rra 2oom! - In ㅗ + 2x10 0.5*0.99 200 mt + 1000 la 2.02 2 = 200 + 500 x0,703 200 t 351.5 551.5ml Threshold gain Co-efficient the 551.5 51.5ml ca) Given h= 1.46 Brewester Tano o angle an Op = Tant (1:46) they 55.60 At this angle will minimise the Loss of P- polarised light. Each Window i e 2 oth th gives 0.25 1 per each pass for AR Coated. 551.5 sml 0.25 x 551.5 To 1 551.5 + 1.4 552.9 553 - 11 = ye for 8th for P- polarised light 553 n! high because away from the medium, It does not amplity, S. polarised is very if leakes