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+{
+ "metadata": {
+  "name": "",
+  "signature": "sha256:ac80f9dfe1725f11a5d4ce0fbda5ffed825d99c680f116629e5e3fcb8b69c198"
+ },
+ "nbformat": 3,
+ "nbformat_minor": 0,
+ "worksheets": [
+  {
+   "cells": [
+    {
+     "cell_type": "heading",
+     "level": 1,
+     "metadata": {},
+     "source": [
+      "Lasers"
+     ]
+    },
+    {
+     "cell_type": "heading",
+     "level": 2,
+     "metadata": {},
+     "source": [
+      "Example number 2.1, Page number 52"
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "#To calculate the relative population \n",
+      "\n",
+      "#importing modules\n",
+      "import math\n",
+      "\n",
+      "#Variable declaration\n",
+      "lamda = 590;        #wavelength(nm)\n",
+      "h = 6.625*10**-34;       #planck's constant\n",
+      "c = 3*10**8;            #velocity of light(m/s)\n",
+      "k = 1.38*10**-23;       #boltzmann's constant\n",
+      "T = 523;                #temperature(Kelvin)\n",
+      "\n",
+      "#Calculation\n",
+      "lamda = lamda*10**-9;      #wavelength(m)      \n",
+      "#n1byn2 = math.exp(-(E2-E1)/(k*T))\n",
+      "#but E2-E1 = h*new and new = c/lamda\n",
+      "#therefore n1byn2 = math.exp(-h*c/(lamda*k*T))\n",
+      "n1byn2 = math.exp(-h*c/(lamda*k*T));\n",
+      "\n",
+      "#Result\n",
+      "print \"relative population of Na atoms is\",n1byn2"
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "relative population of Na atoms is 5.36748316686e-21\n"
+       ]
+      }
+     ],
+     "prompt_number": 1
+    },
+    {
+     "cell_type": "heading",
+     "level": 2,
+     "metadata": {},
+     "source": [
+      "Example number 2.2, Page number 53"
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "#To calculate the ratio of stimulated to spontaneous emission \n",
+      "\n",
+      "#importing modules\n",
+      "import math\n",
+      "\n",
+      "#Variable declaration\n",
+      "lamda = 590;        #wavelength(nm)\n",
+      "h = 6.625*10**-34;       #planck's constant\n",
+      "c = 3*10**8;            #velocity of light(m/s)\n",
+      "k = 1.38*10**-23;       #boltzmann's constant\n",
+      "T = 523;                #temperature(Kelvin)\n",
+      "\n",
+      "#Calculation\n",
+      "lamda = lamda*10**-9;      #wavelength(m)      \n",
+      "#n21dashbyn21 = 1/(math.exp(h*new/(k*T))-1)\n",
+      "#but new = c/lamda\n",
+      "#therefore n21dashbyn21 = 1/(math.exp(h*c/(lamda*k*T))-1)\n",
+      "A = math.exp(h*c/(lamda*k*T))-1;\n",
+      "n21dashbyn21 = 1/A;    \n",
+      "\n",
+      "#Result\n",
+      "print \"ratio of stimulated to spontaneous emission is\",n21dashbyn21\n",
+      "print \"answer given in the book is wrong\""
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "ratio of stimulated to spontaneous emission is 5.36748316686e-21\n",
+        "answer given in the book is wrong\n"
+       ]
+      }
+     ],
+     "prompt_number": 4
+    },
+    {
+     "cell_type": "heading",
+     "level": 2,
+     "metadata": {},
+     "source": [
+      "Example number 2.3, Page number 53"
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "#To calculate the number of photons emitted \n",
+      "\n",
+      "#importing modules\n",
+      "import math\n",
+      "\n",
+      "#Variable declaration\n",
+      "lamda = 632.8;        #wavelength of laser(nm)\n",
+      "h = 6.625*10**-34;       #planck's constant\n",
+      "c = 3*10**8;            #velocity of light(m/s)\n",
+      "p = 3.147;              #output power(mW)\n",
+      "\n",
+      "#Calculation\n",
+      "p = p*10**-3;          #output power(W)\n",
+      "lamda = lamda*10**-9;      #wavelength(m)      \n",
+      "new = c/lamda;             #frequency(Hz)\n",
+      "E = h*new;                 #energy of each photon(J)\n",
+      "Em = p*60;                 #energy emitted per minute(J/min)\n",
+      "N = Em/E;                  #number of photons emitted per second\n",
+      "\n",
+      "#Result\n",
+      "print \"number of photons emitted per second is\",N"
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "number of photons emitted per second is 6.01183879245e+17\n"
+       ]
+      }
+     ],
+     "prompt_number": 5
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [],
+     "language": "python",
+     "metadata": {},
+     "outputs": []
+    }
+   ],
+   "metadata": {}
+  }
+ ]
+}
+\ No newline at end of file