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  {
   "cells": [
    {
     "cell_type": "heading",
     "level": 1,
     "metadata": {},
     "source": [
      "10: Lasers"
     ]
    },
    {
     "cell_type": "heading",
     "level": 2,
     "metadata": {},
     "source": [
      "Example number 10.1, Page number 10.6"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "#importing modules\n",
      "import math\n",
      "from __future__ import division\n",
      "\n",
      "#Variable declaration\n",
      "c = 3*10**8    #speed of light(m/sec)\n",
      "h = 6.6*10**-34    #planck's constant\n",
      "e = 1.6*10**-19\n",
      "T = 300    #temperature(K)\n",
      "K = 8.61*10**-5\n",
      "lamda = 6943    #wavelength, angstrom\n",
      "\n",
      "#Calculation\n",
      "lamda = lamda*10**-10     #wavelength(m)\n",
      "#let E2 - E1 be E\n",
      "E = h*c/lamda      #energy(J)\n",
      "E = E/e       #energy(eV)\n",
      "#let population ratio N2/N1 be N\n",
      "N = math.exp(-E/(K*T));\n",
      "\n",
      "#Result\n",
      "print \"relative population of 2 states is\",round(N/1e-30,3),\"*10^-30\"\n",
      "print \"answer given in the book is wrong\""
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "relative population of 2 states is 1.076 *10^-30\n",
        "answer given in the book is wrong\n"
       ]
      }
     ],
     "prompt_number": 2
    },
    {
     "cell_type": "heading",
     "level": 2,
     "metadata": {},
     "source": [
      "Example number 10.2, Page number 10.14"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "#importing modules\n",
      "import math\n",
      "from __future__ import division\n",
      "\n",
      "#Variable declaration\n",
      "a2 = 6     #spot diameter(mm)\n",
      "a1 = 4     #spot diameter(mm)\n",
      "d2 = 2    #distance from laser(m)\n",
      "d1 = 1    #distance from laser(m)\n",
      "\n",
      "#Calculation\n",
      "a2 = a2*10**-3    #spot diameter(m)\n",
      "a1 = a1*10**-3     #spot diameter(m)\n",
      "theta = (a2-a1)/(2*(d2-d1))     #divergence(radian)\n",
      "theta = theta*10**3      #divergence(milli radian)\n",
      "\n",
      "#Result\n",
      "print \"divergence is\",theta,\"milli radian\""
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "divergence is 1.0 milli radian\n"
       ]
      }
     ],
     "prompt_number": 3
    },
    {
     "cell_type": "heading",
     "level": 2,
     "metadata": {},
     "source": [
      "Example number 10.3, Page number 10.46"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "#importing modules\n",
      "import math\n",
      "from __future__ import division\n",
      "\n",
      "#Variable declaration\n",
      "n = 1     #for air\n",
      "lamda = 650     #wavelength(nm)\n",
      "bs = 1     #beam size(mm)\n",
      "fl = 1    #focal length of lens(mm)\n",
      "\n",
      "#Calculation\n",
      "lamda = lamda*10**-9    #wavelength(m)\n",
      "bs = bs*10**-3    #beam size(m)\n",
      "fl = fl*10**-3     #focal length of lens(m)\n",
      "tan_theta = fl/(2*bs)     #value of tan_theta\n",
      "theta = math.atan(tan_theta)\n",
      "NA = n*math.sin(theta)\n",
      "NA = math.ceil(NA*10**2)/10**2;   #rounding off to 2 decimals\n",
      "ss = 0.6*lamda/NA       #spot size(m)\n",
      "ss = ss*10**6;       #spot size(micro metre)\n",
      "ss = math.ceil(ss*10**3)/10**3;   #rounding off to 4 decimals\n",
      "\n",
      "#Result\n",
      "print \"spot size is\",ss,\"micro metre\""
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "spot size is 0.867 micro metre\n"
       ]
      }
     ],
     "prompt_number": 6
    }
   ],
   "metadata": {}
  }
 ]
}