# 10: Lasers¶

## Example number 10.1, Page number 10.6¶

In [2]:
#importing modules
import math
from __future__ import division

#Variable declaration
c = 3*10**8    #speed of light(m/sec)
h = 6.6*10**-34    #planck's constant
e = 1.6*10**-19
T = 300    #temperature(K)
K = 8.61*10**-5
lamda = 6943    #wavelength, angstrom

#Calculation
lamda = lamda*10**-10     #wavelength(m)
#let E2 - E1 be E
E = h*c/lamda      #energy(J)
E = E/e       #energy(eV)
#let population ratio N2/N1 be N
N = math.exp(-E/(K*T));

#Result
print "relative population of 2 states is",round(N/1e-30,3),"*10^-30"
print "answer given in the book is wrong"

relative population of 2 states is 1.076 *10^-30
answer given in the book is wrong


## Example number 10.2, Page number 10.14¶

In [3]:
#importing modules
import math
from __future__ import division

#Variable declaration
a2 = 6     #spot diameter(mm)
a1 = 4     #spot diameter(mm)
d2 = 2    #distance from laser(m)
d1 = 1    #distance from laser(m)

#Calculation
a2 = a2*10**-3    #spot diameter(m)
a1 = a1*10**-3     #spot diameter(m)

#Result

divergence is 1.0 milli radian


## Example number 10.3, Page number 10.46¶

In [6]:
#importing modules
import math
from __future__ import division

#Variable declaration
n = 1     #for air
lamda = 650     #wavelength(nm)
bs = 1     #beam size(mm)
fl = 1    #focal length of lens(mm)

#Calculation
lamda = lamda*10**-9    #wavelength(m)
bs = bs*10**-3    #beam size(m)
fl = fl*10**-3     #focal length of lens(m)
tan_theta = fl/(2*bs)     #value of tan_theta
theta = math.atan(tan_theta)
NA = n*math.sin(theta)
NA = math.ceil(NA*10**2)/10**2;   #rounding off to 2 decimals
ss = 0.6*lamda/NA       #spot size(m)
ss = ss*10**6;       #spot size(micro metre)
ss = math.ceil(ss*10**3)/10**3;   #rounding off to 4 decimals

#Result
print "spot size is",ss,"micro metre"

spot size is 0.867 micro metre