# Chapter 4: Laser¶

## Example 4.1,Page number 4-27¶

In [1]:
import math

#Given Data:
lamda=694.3*10**-9         #Wavelength in meter
T=300                   #Temperature in Kelvin

h=6.63*10**-34           #Planck's Constant
c=3*10**8                #Velocity of light
K=1.38*10**-21           #Boltzmann Constant

#Calculations:
delE= h*c/lamda           #Energy difference between two energy states N and N0

#N=N0*e^-delE/(K*T)
R=math.e**(-delE/(K*T))      #R=Ratio of N and N0 i.e.(R=N/N0)

#(Printing mistake in textbook)
#instead of e^-.692, it has taken e^-69.2

print"The ratio of population of two energy states is = ",R
print" (calculation mistake in book)"

The ratio of population of two energy states is =  0.500588928485
(calculation mistake in book)


## Example 4.2,Page number 4-28¶

In [3]:
import math

#Given Data:
lamda=6328*10**-10        #Wavelength in meter
P=4.5*10**-3              #Power in watts
h=6.63*10**-34           #Planck's Constant
c=3*10**8                 #Velocity of light

#Calculations:
delE= h*c/lamda           #Energy difference
#N*delE=P
N=P/delE                #number of photons emitted per second

print"Number of photons emitted per second is =",N

Number of photons emitted per second is = 1.43167420814e+16


## Example 4.3,Page number 4-29¶

In [6]:
import math

#Given Data:
lamda=780*10**-9           #Wavelength of photon in meter
P=20*10**-3              #Power of each pulse in watts
t=10*10**-9              #Duration of each pulse
h=6.63*10**-34           #Planck's Constant
c=3*10**8                #Velocity of light

#Calculations:
delE= h*c/lamda           #Energy of each photon
E=P*t                   #Energy of each pulse

N=E/delE                #Number of photons in each pulse
print"Number of photons in each pulse is =",N

Number of photons in each pulse is = 784313725.49

In [ ]: