Chapter 4 Laser

Example 4.1 Page no 164

In [16]:
#Given
w=6328.0*10**-10                       #m
K=1.38*10**-23                #J/k
T=300                        #K
e=6.63*10**-34
c=3*10**8

#Calculation
E=e*c/w
N=math.exp(-E/(K*T))

#Result
print"Ratio of population of two states is", round(N*10**33,0)*10**-33

Ratio of population of two states is 1e-33

Example 4.2 Page no 164

In [15]:
#Given
N=1.059*10**-30
T=330
K=1.38*10**-23                    #J/K
E=3.147*10**-19
c=3*10**8
h=6.63*10**-34

#Calculation
w=h*c/E

#Result
print"Wavelength of light is",round(w*10**9,0),"*10**-9 m"

Wavelength of light is 632.0 *10**-9 m

Example 4.3 Page no 165

In [3]:
#Given
v=3000.0                     #bandwidth in Hz
c=3*10**8                    #speed of light in m/ s

#Calculation
t =1/ v
l=(c*t)

#Result
print"Coherence length for laser is",l*10**-3,"km"

Coherence length for laser is 100.0 km

Example 4.4 Page no 165

In [17]:
#Given
theta =32                     #angle on slit in second
w=5*10**-5

#Calculation
theta1 =theta* 3.14/(60*180) 
C=w/ theta1

#Result
print"Transverse coherence length is",round(C,3),"cm"

Transverse coherence length is 0.005 cm

Example 4.5 Page no 165

In [3]:
#Given
t=1.0*10**-10                      #coherence time in sec
c=3*10**8                     #speed of light in m/ s
w =54.0*10**-8                  #wave length of nonô€€€monochromacity in m

#Calclation
B =1/ t
v=c/w
D=B/v

#Result
print"Degree is",D

Degree is 1.8e-05

Example 4.6 Page no 166

In [24]:
#Given
t=5.0*10**-10                 #s
c=3*10**8

#Calculation
l=t*c
v=1/t

#Result
print"Coherence length is", v*10**-9,"*10**9 Hz"

Coherence length is 2.0 *10**9 Hz

Example 4.7 Page no 166

In [33]:
#Given
L=7200*10**-10                       #m
d=5*10**-3
f=0.1
p=50*10**-3

#Calculation
a=L/d
A=a**2*f**2
I=p/A

#Result
print"Area of image is", A,"m**2"
print"Intensity of image is",round(I*10**-8,3),"*10**8 W/m**2"

Area of image is 2.0736e-10 m**2
Intensity of image is 2.411 *10**8 W/m**2

Example 4.8 Page no 166

In [47]:
#Given
w=7*10**-7                         #m
a=5.0*10**-3
D=4*10**8

#Calculation
A=1.22*w/a
x=(D*A)**2*3.14

#Result
print"(i) The angular spread is",round(A*10**4,1),"*10**-4 radian"
print"(ii) Areal spread when the beam reaches the moon is", round(x*10**-10,2),"*10**10 m**2"

(i) The angular spread is 1.7 *10**-4 radian
(ii) Areal spread when the nbeam reaches the moon is 1.47 *10**10 m**2

Example 4.9 Page no 167

In [50]:
#Given
L=0.5                         #m

#Calculation
v=c/(2*L)

#Result
print"Mode separation of longitudinal cavity is",v*10**-8,"*10**8 Hz"

Mode separation of longitudinal cavity is 3.0 *10**8 Hz