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// Example no.3.11
// To calculate (a) the optical gain coefficient Γg required to balance the cavity loss and (b) the threshold electron density Ne
// Page no.135
clc;
clear;
// Given data
L=320*10^-6; // Cavity length
R1=0.35; // The reflectivity of ligth wave which is reflected at A
R2=0.35; // The reflectivity of ligth wave which is reflected at B
aint=10^3; // Internal cavity loss in m^-1
c=3*10^8; // Speed of ligth in air
Go=1.73*10^-12; // Gain coefficient in m^3/s
Neo=3.47*10^23; // The value of the carrier density at which the gain coefficient becomes zero in m^-3
n=3.3; // Refractive index of medium
// (a) the optical gain coefficient Γg required to balance the cavity loss
amir=(1/(2*L))*log(1/(R1*R2)); // The loss due to mirrors per m
acav=amir+aint; // The total cavity loss coefficient
gammag=acav; // The optical gain coefficient in m^-1
// Displaying the result in command window
printf('\n The optical gain coefficient = %0.2f X 10^3 m^-1',gammag*10^-3);
//(b) the threshold electron density Ne
v=c/n; // Velocity of ligth in medium
Tph=1/(v*acav); // The photon lifetime in sec
Neth=Neo+1/(Go*Tph); // The threshold electron density Ne
// Displaying the result in command window
printf('\n The threshold electron density = %0.2f X 10^23 m^-3',Neth*10^-23);
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