# 5: Laser¶

## Example number 5.1, Page number 124¶

In :
#importing modules
import math
from __future__ import division

#Variable declaration
t=300;    #temperature(K)
w=698.3*10**-9;   #wavelength of photon(m)
h=6.625*10**-34;  #Planck's constant(m^2 Kg/sec)
c=3*10**8;     #velocity of light(m/s)
Kb=1.38*10**-23;   #Boltzmann's constant(m^2 Kg.s^-2 k^-1)

#Calculation
Ratio=math.exp((-h*c)/(w*Kb*t));    #ratio of propulsion of the two states in a laser

#Result
print "The ratio of propulsion of the two states in a laser is",round(Ratio*10**30,4),"*10**-30"

The ratio of propulsion of the two states in a laser is 1.3893 *10**-30


## Example number 5.2, Page number 133¶

In :
#importing modules
import math
from __future__ import division

#Variable declaration
w=1.55*10**-6;   #wavelength of light emission(m)
h=6.625*10**-34;  #Planck's constant(m^2 Kg/sec)
c=3*10**8;    #velocity of light(m/s)
e=1.6*10**-19;   #charge of electron(c)

#Calculation
Eg=(h*c)/(w*e);    #band gap(eV)

#Result
print "The band gap for lnp laser diode is",round(Eg,4),"eV"

The band gap for lnp laser diode is 0.8014 eV


## Example number 5.3, Page number 133¶

In :
#importing modules
import math
from __future__ import division

#Variable declaration
E=0.02*1.6*10**-19;    #Ionisation energy(J)
h=6.625*10**-34;    #Planck's constant(m^2 Kg/sec)
c=3*10**8;        #velocity of light(m/s)

#Calculation
w=h*c/E;       #long wavelength limit of an extrinsic semiconductor(m)

#Result
print "The long wavelength limit of an extrinsic semiconductor is",round(w*10**5,4),"*10**-5 m"

The long wavelength limit of an extrinsic semiconductor is 6.2109 *10**-5 m


## Example number 5.4, Page number 133¶

In :
#importing modules
import math
from __future__ import division

#Variable declaration
E=3.5*10**-3*60;    #power output(J/min)
w=0.621*10**-6;     #wavelength of light(m)
h=6.625*10**-34;    #Planck's constant(m^2 Kg/sec)
c=3*10**8;       #velocity of light(m/s)

#Calculation
e=h*c/w;      #energy emitted by one photon(J)
n=E/e;     #The number of photons emitted per minute(photons/minute)

#Result
print "The number of photons emitted per minute is",round(n/10**17,3),"*10**17 photons/minute"

The number of photons emitted per minute is 6.562 *10**17 photons/minute