# Chapter 4: Lasers¶

## Example 4.6.1, Page number 4-7¶

In [2]:
#Variable declaration
P = 3.147*10**-3     #output power(W)
t = 60               #time(sec)
lamda = 632.8*10**-9 #wavelength(m)
h = 6.63*10**-34     #Planc's constant(J-s)
c = 3*10**8          #velocity of light(m/s)

#Calculations
N = (P*t*lamda)/(h*c)

#Result
print "No. of photons emittd each minute is",round(N/1e+17),"*10^17"

No. of photons emittd each minute is 6.0 *10^17


## Example 4.6.2, Page number 4-7¶

In [4]:
import math

#Variable declaration
T = 300              #temperature(K)
lamda = 694.3*10**-9 #wavelength(m)
h = 6.63*10**-34     #Planc's constant(J-s)
c = 3*10**8          #velocity of light(m/s)
k = 1.38*10**-23     #Boltman's constant(J/K)

#Calculations
N2_by_N1 = math.exp((-h*c)/(lamda*k*T))

#Result
print "Ratio of population =",round(N2_by_N1/1e-31,3),"*10^-31"

Ratio of population = 8.874 *10^-31


## Example 4.6.3, Page number 4-8¶

In [8]:
#Variable declaration
P = 100*10**3        #output power(W)
t = 20*10**-9        #time(sec)
N = 6.981*10**15     #no. of photons
h = 6.63*10**-34     #Planc's constant(J-s)
c = 3*10**8          #velocity of light(m/s)

#Calculations
lamda = (N*h*c)/(P*t)

#Result
print "Wavelength =",round(lamda/1e-10),"A"

Wavelength = 6943.0 A