Chapter 6: Lasers

Example 6.1, Page 170

In [1]:
#Variable Declaration
D=4*1e8;#distance between earth and moon in m
lamda=16000.*1e-10;#wavelength in meters
d=1e-3;#aperture in meter

#Calculations & Result
th=lamda/d;#angular speed
print 'angular speed is=',th,'rad'
aos=(D*th)**2;#area of spread 
print 'area of spread is=',aos,'m^2'
#Incorrect answer in the textbook

angular speed is= 0.0016 rad
area of spread is= 4.096e+11 m^2

Example 6.2, Page 170

In [2]:
#Variable Declaration
a1=2*1e-3;#distance from the laser
a2=3*1e-3;#distance from the laser
d1=2;#output beam spot diameter
d2=4;#output beam spot diameter

#Calculation
th=(a2-a1)/(2*(d2-d1));#angle of divergence

#Result
print 'angle of divergence',th/1e-3,'*10^-3 rad'

angle of divergence 0.25 *10^-3 rad

Example 6.3, Page 171

In [3]:
#Variable Declaration
D=0.1;#focal length of lens
lamda=14400*1e-10;#wavelength in meters
p=100*1e-3;#power of laser beam
d=10*1e-3;#aperture in meter

#Calculations & Results
th=lamda/d;#angular speed
print 'angular speed is=',th/1e-4,'*10^-4 rad'
aos=(D*th)**2;#area of spread 
print 'area of spread is=',aos/1e-10,'*10^-10 m^2'
I=p/aos;#'intensity
print 'intensity is=',round(I/1e7,1),'*10^7 W*m^-2'

angular speed is= 1.44 *10^-4 rad
area of spread is= 2.0736 *10^-10 m^2
intensity is= 48.2 *10^7 W*m^-2