# 11: Laser¶

## Example number 11.1, Page number 246¶

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

#Variable declaration
e=1.6*10**-19;     #charge(coulomb)
v=3*10**3;   #velocity of matter wave(m/s)
h=6.6*10**-34;    #plank's constant(Js)
lamda=600*10**-9;    #wavelength(m)

#Calculation
Ej=h*v/lamda;    #matter wave energy(J)
E=Ej/e;      #matter wave energy(eV)

#Result
print "matter wave energy is",round(E*10**5,2),"*10**-5 eV"
print "answer given in the book is wrong"

matter wave energy is 2.06 *10**-5 eV
answer given in the book is wrong


## Example number 11.2, Page number 246¶

In [3]:
#importing modules
import math
from __future__ import division

#Variable declaration
e=1.6*10**-19;     #charge(coulomb)
c=3*10**10;   #velocity of light(m/s)
h=6.6*10**-34;    #plank's constant(Js)
Eg=3;    #energy gap(eV)

#Calculation
lamda=h*c*10**9/(Eg*e);     #wavelength of photon(nm)

#Result
print "wavelength of photon is",lamda,"nm"
print "answer given in the book is wrong"

wavelength of photon is 41250.0 nm
answer given in the book is wrong


## Example number 11.3, Page number 246¶

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

#Variable declaration
e=1.6*10**-19;     #charge(coulomb)
E2_E1=3*e;    #energy gap(J)
Kb=1.38*10**-23;    #boltzmann constant(J/K)
T=323;    #temperature(K)

#Calculation
n=math.exp(-E2_E1/(Kb*T));    #ratio in higher and lower energy

#Result
print "ratio in higher and lower energy is",round(n*10**47,4),"*10**-47"
print "answer given in the book is wrong"

ratio in higher and lower energy is 1.7081 *10**-47
answer given in the book is wrong


## Example number 11.4, Page number 247¶

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

#Variable declaration
c=2.998*10**8;     #velocity of light(m/s)
Kb=1.381*10**-23;    #boltzmann constant(J/K)
T=1000;    #temperature(K)
h=6.626*10**-34;    #plank's constant(Js)
lamda=0.5*10**-6;   #wavelength(m)

#Calculation
v=c/lamda;    #frequency(Hz)
BA=1/(math.exp(h*v/(Kb*T))-1);      #ratio of emission

#Result
print "ratio of emission is",round(BA*10**13,1),"*10**-13"
print "answer varies due to rounding off errors"

ratio of emission is 3.2 *10**-13
answer varies due to rounding off errors


## Example number 11.5, Page number 247¶

In [6]:
#importing modules
import math
from __future__ import division

#Variable declaration
c=2.998*10**8;     #velocity of light(m/s)
h=6.626*10**-34;    #plank's constant(Js)
e=1.602*10**-19;     #charge(coulomb)
Eg=1.43;    #energy gap(eV)

#Calculation
lamda=h*c*10**6/(Eg*e);        #wavelength(micro m)

#Result
print "wavelength is",round(lamda,2),"micro m"

wavelength is 0.87 micro m