# 12: Lasers¶

## Example number 1, Page number 12.30¶

In [5]:
#importing modules
import math
from __future__ import division

#Variable declaration
h=6.626*10**-34;       #plancks constant(J s)
c=3*10**8;             #velocity of light(m/s)
lamda=6943*10**-10;    #wavelength of emission(m)
k=1.38*10**-23;        #boltzmann constant
T=300;                 #temperature(K)

#Calculation
new=c/lamda;           #frequency(Hz)
x=h*new/(k*T);
N1byN2=math.exp(x);    #relative population in laser transition levels

#Result
print "relative population in laser transition levels is",round(N1byN2/10**30,3),"*10**30"
print "answer given in the book is wrong"

relative population in laser transition levels is 1.081 *10**30
answer given in the book is wrong


## Example number 2, Page number 12.31¶

In [10]:
#importing modules
import math
from __future__ import division

#Variable declaration
h=6.626*10**-34;       #plancks constant(J s)
P=2.3*10**-3;          #output power(W)
t=1;                   #time(sec)
new=4.74*10**14;       #frequency(Hz)
s=1*10**-6;            #spot area(m**2)

#Calculation
n=P*t/(h*new);         #number of photons emitted in each second
Pd=P/s;                #power density(W/m**2)

#Result
print "number of photons emitted is",round(n/10**15,3),"*10**15 photons/second"
print "power density is",Pd/10**3,"kW/m**2"

number of photons emitted is 7.323 *10**15 photons/second
power density is 2.3 kW/m**2


## Example number 3, Page number 12.31¶

In [2]:
#importing modules
import math
from __future__ import division

#Variable declaration
h=6.626*10**-34;       #plancks constant(J s)
c=3*10**8;     #velocity of light(m/s)
Eg=1.44*1.6*10**-19;    #band gap(J)

#Calculation
lamda=h*c/Eg;      #wavelength of emission(m)

#Result
print "wavelength of emission is",int(round(lamda*10**10)),"angstrom"

wavelength of emission is 8628 angstrom