# 12: Lasers¶

## Example number 12.1, Page number 12.5¶

In [4]:
#importing modules
import math
from __future__ import division

#Variable declaration
e=1.6*10**-19;     #charge(coulomb)
h=6.6*10**-34;     #planck's constant(J sec)
c=3*10**8;     #velocity of light(m/sec)
lamda=6943*10**-10;     #wavelength(m)
k=8.61*10**-5;
T=300;    #temperature(K)

#Calculation
dE=h*c/(e*lamda);
N2byN1=math.exp(-dE/(k*T));     #relative population

#Result
print "relative population is",round(N2byN1*10**30,4),"*10**-30"
print "answer given in the book is wrong"

relative population is 1.0764 *10**-30
answer given in the book is wrong


## Example number 12.2, Page number 12.13¶

In [7]:
#importing modules
import math
from __future__ import division

#Variable declaration
a1=4*10**-3;      #diameter(m)
a2=6*10**-3;      #diameter(m)
d1=1;     #distance(m)
d2=2;     #distance(m)

#Calculation

#Result

divergence is 1.0 milli radian


## Example number 12.3, Page number 12.45¶

In [12]:
#importing modules
import math
from __future__ import division

#Variable declaration
s=1*10**-3;    #size(m)
l=1*10**-3;    #length(m)
lamda=650*10**-9;    #wavelength(m)

#Calculation
tantheta=(l/2)/s;

spot size is 0.867 micro m