# Chapter 7:LASERS¶

## Example 7.1, Page number 7.32¶

In [4]:
import math
from __future__ import division

#variable declaration
d1 = 4;                #Converting from mm to radians
d2 = 6;                #Converting from mm to radians

#calculations
D = (r2-r1)/(d2*10**3-d1*10**3)   #Divergence

#Result

Divergence = -2.0 *10**-3 radian


## Example 7.2, Page number 7.32¶

In [1]:
import math
from __future__ import division

#variable declaration
C=3*10**8                    #The speed of light
Lamda=6943                   #Wavelength
T=300                        #Temperature in Kelvin
h=6.626*10**-34              #Planck constant
k=1.38*10**-23               #Boltzmann's constant

#Calculations

V=(C)/(Lamda*10**-10)       #Frequency
R=math.exp(h*V/(k*T))       #Relative population

#Result
print "Frequency (V) =",round(V/10**14,2),"*10**14 Hz"
print "Relative Population=",round(R/10**30,3),"*10**30"

Frequency (V) = 4.32 *10**14 Hz
Relative Population= 1.081 *10**30


## Example 7.3, Page number 7.32¶

In [2]:
import math
from __future__ import division

#variable declaration
C=3*10**8                     #Velocity of light
W=632.8*10**-9                #wavelength
P=2.3
t=1
h=6.626*10**-34              #Planck constant
S=1*10**-6

#Calculations
V=C/W                        #Frequency
n=((P*10**-3)*t)/(h*V)       #no.of photons emitted
PD=P*10**-3/S                #Power density

#Result
print "Frequency=",round(V/10**14,2),"*10**14 Hz"
print "no.of photons emitted=",round(n/10**15,3),"*10**15 photons/sec"
print "Power density =",round(PD/1000,1),"kWm**-2"

 Frequency= 4.74 *10**14 Hz
no.of photons emitted= 7.322 *10**15 photons/sec
Power density = 2.3 kWm**-2


## Example 7.4, Page number 7.33¶

In [1]:
import math
from __future__ import division

#variable declaration
h=6.626*10**-34              #Planck constant
C=3*10**8                    #Velocity of light
E_g=1.44                     #bandgap

#calculations
lamda=(h*C)*10**10/(E_g*1.6*10**-19)       #Wavelenght

#Result
print "Wavelenght =",round(lamda),"Angstrom"

Wavelenght = 8628.0 Angstrom


## Example 7.5, Page number 7.33¶

In [25]:
import math
from __future__ import division

#variable declaration
W=1.55                       #wavelength

#Calculations
E_g=(1.24)/W                 #Bandgap in eV

#Result
print "Band gap =",E_g,"eV"

Band gap = 0.8 eV