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+{
+ "metadata": {
+  "name": ""
+ },
+ "nbformat": 3,
+ "nbformat_minor": 0,
+ "worksheets": [
+  {
+   "cells": [
+    {
+     "cell_type": "heading",
+     "level": 1,
+     "metadata": {},
+     "source": [
+      "Chapter 4: Lasers"
+     ]
+    },
+    {
+     "cell_type": "heading",
+     "level": 2,
+     "metadata": {},
+     "source": [
+      "Example 4.6.1, Page number 4-7"
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "\n",
+      "#Variable declaration\n",
+      "P = 3.147*10**-3     #output power(W)\n",
+      "t = 60               #time(sec)\n",
+      "lamda = 632.8*10**-9 #wavelength(m)\n",
+      "h = 6.63*10**-34     #Planc's constant(J-s)\n",
+      "c = 3*10**8          #velocity of light(m/s)\n",
+      "\n",
+      "#Calculations\n",
+      "N = (P*t*lamda)/(h*c)\n",
+      "\n",
+      "#Result\n",
+      "print \"No. of photons emittd each minute is\",round(N/1e+17),\"*10^17\""
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "No. of photons emittd each minute is 6.0 *10^17\n"
+       ]
+      }
+     ],
+     "prompt_number": 2
+    },
+    {
+     "cell_type": "heading",
+     "level": 2,
+     "metadata": {},
+     "source": [
+      "Example 4.6.2, Page number 4-7"
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "\n",
+      "import math\n",
+      "\n",
+      "#Variable declaration\n",
+      "T = 300              #temperature(K)\n",
+      "lamda = 694.3*10**-9 #wavelength(m)\n",
+      "h = 6.63*10**-34     #Planc's constant(J-s)\n",
+      "c = 3*10**8          #velocity of light(m/s)\n",
+      "k = 1.38*10**-23     #Boltman's constant(J/K)\n",
+      "\n",
+      "#Calculations\n",
+      "N2_by_N1 = math.exp((-h*c)/(lamda*k*T))\n",
+      "                    \n",
+      "#Result\n",
+      "print \"Ratio of population =\",round(N2_by_N1/1e-31,3),\"*10^-31\""
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "Ratio of population = 8.874 *10^-31\n"
+       ]
+      }
+     ],
+     "prompt_number": 4
+    },
+    {
+     "cell_type": "heading",
+     "level": 2,
+     "metadata": {},
+     "source": [
+      "Example 4.6.3, Page number 4-8"
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "\n",
+      "#Variable declaration\n",
+      "P = 100*10**3        #output power(W)\n",
+      "t = 20*10**-9        #time(sec)\n",
+      "N = 6.981*10**15     #no. of photons\n",
+      "h = 6.63*10**-34     #Planc's constant(J-s)\n",
+      "c = 3*10**8          #velocity of light(m/s)\n",
+      "\n",
+      "#Calculations\n",
+      "lamda = (N*h*c)/(P*t)\n",
+      "\n",
+      "#Result\n",
+      "print \"Wavelength =\",round(lamda/1e-10),\"A\""
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "Wavelength = 6943.0 A\n"
+       ]
+      }
+     ],
+     "prompt_number": 8
+    }
+   ],
+   "metadata": {}
+  }
+ ]
+}
+\ No newline at end of file