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+{
+ "metadata": {
+  "name": "",
+  "signature": "sha256:ecf05dc207884a73f4d33d07fdee310eee827214d9664476e0cf941cf4d4f512"
+ },
+ "nbformat": 3,
+ "nbformat_minor": 0,
+ "worksheets": [
+  {
+   "cells": [
+    {
+     "cell_type": "heading",
+     "level": 1,
+     "metadata": {},
+     "source": [
+      "11: Lasers"
+     ]
+    },
+    {
+     "cell_type": "heading",
+     "level": 2,
+     "metadata": {},
+     "source": [
+      "Example number 11.1, Page number 249"
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "\n",
+      "#importing modules\n",
+      "import math\n",
+      "from __future__ import division\n",
+      "\n",
+      "#Variable declaration\n",
+      "h = 6.626*10**-34;     #Planck's constant(Js)\n",
+      "c = 3*10**8;     #Speed of light in free space(m/s)\n",
+      "k = 1.38*10**-23;     #Boltzmann constant(J/K)\n",
+      "T = 300;     #Temperature at absolute scale(K)\n",
+      "lamda1 = 5500;     #Wavelength of visible light(A)\n",
+      "lamda2 = 10**-2;     #Wavelength of microwave(m)\n",
+      "\n",
+      "#Calculation\n",
+      "lamda1 = lamda1*10**-10;     #Wavelength of visible light(m)\n",
+      "rate_ratio = math.exp(h*c/(lamda1*k*T))-1;    #Ratio of spontaneous emission to stimulated emission\n",
+      "rate_ratio1 = math.exp(h*c/(lamda2*k*T))-1;     #Ratio of spontaneous emission to stimulated emission\n",
+      "rate_ratio1 = math.ceil(rate_ratio1*10**5)/10**5;     #rounding off the value of rate_ratio1 to 5 decimals\n",
+      "\n",
+      "#Result\n",
+      "print \"The ratio of spontaneous emission to stimulated emission for visible region is\",rate_ratio\n",
+      "print \"The ratio of spontaneous emission to stimulated emission for microwave region is\", rate_ratio1"
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "The ratio of spontaneous emission to stimulated emission for visible region is 8.19422217477e+37\n",
+        "The ratio of spontaneous emission to stimulated emission for microwave region is 0.00482\n"
+       ]
+      }
+     ],
+     "prompt_number": 3
+    },
+    {
+     "cell_type": "heading",
+     "level": 2,
+     "metadata": {},
+     "source": [
+      "Example number 11.2, Page number 250"
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "\n",
+      "\n",
+      "#importing modules\n",
+      "import math\n",
+      "from __future__ import division\n",
+      "\n",
+      "#Variable declaration\n",
+      "e = 1.6*10**-19;   #Energy equivalent of 1 eV(J/eV)\n",
+      "h = 6.626*10**-34;    #Planck's constant(Js)\n",
+      "c = 3*10**8;    #Speed of light in free space(m/s)\n",
+      "lamda = 690;    #Wavelength of laser light(nm)\n",
+      "E_lower = 30.5;    #Energy of lower state(eV)\n",
+      "\n",
+      "#Calculation\n",
+      "lamda = lamda*10**-9;     #Wavelength of laser light(m)\n",
+      "E = h*c/lamda;    #Energy of the laser light(J)\n",
+      "E = E/e;     #Energy of the laser light(eV)\n",
+      "E_ex = E_lower + E;    #Energy of excited state of laser system(eV)\n",
+      "E_ex = math.ceil(E_ex*10**2)/10**2;     #rounding off the value of E_ex to 2 decimals\n",
+      "\n",
+      "#Result\n",
+      "print \"The energy of excited state of laser system is\",E_ex, \"eV\""
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "The energy of excited state of laser system is 32.31 eV\n"
+       ]
+      }
+     ],
+     "prompt_number": 4
+    },
+    {
+     "cell_type": "heading",
+     "level": 2,
+     "metadata": {},
+     "source": [
+      "Example number 11.3, Page number 250"
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "\n",
+      "#importing modules\n",
+      "import math\n",
+      "from __future__ import division\n",
+      "import numpy as np\n",
+      "\n",
+      "#Variable declaration\n",
+      "h = 6.626*10**-34;     #Planck's constant(Js)\n",
+      "k = 1.38*10**-23;      #Boltzmann constant(J/K)\n",
+      "\n",
+      "#Calculation\n",
+      "#Stimulated Emission = Spontaneous Emission <=> exp(h*f/(k*T))-1 = 1 i.e.\n",
+      "#f/T = log(2)*k/h = A\n",
+      "A =  np.log(2)*k/h;     #Frequency per unit temperature(Hz/K)\n",
+      "A = A/10**10;\n",
+      "A = math.ceil(A*10**3)/10**3;     #rounding off the value of A to 3 decimals\n",
+      "\n",
+      "#Result\n",
+      "print \"The stimulated emission equals spontaneous emission iff f/T =\",A,\"*10**10 Hz/k\""
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "The stimulated emission equals spontaneous emission iff f/T = 1.444 *10**10 Hz/k\n"
+       ]
+      }
+     ],
+     "prompt_number": 7
+    },
+    {
+     "cell_type": "heading",
+     "level": 2,
+     "metadata": {},
+     "source": [
+      "Example number 11.4, Page number 250"
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "\n",
+      "\n",
+      "#importing modules\n",
+      "import math\n",
+      "from __future__ import division\n",
+      "\n",
+      "#Variable declaration\n",
+      "lamda = 500;     #Wavelength of laser light(nm)\n",
+      "f = 15;     #Focal length of the lens(cm)\n",
+      "d = 2;      #Diameter of the aperture of source(cm)\n",
+      "P = 5;      #Power of the laser(mW)\n",
+      "\n",
+      "#Calculation\n",
+      "P =  P*10**-3;    #Power of the laser(W)\n",
+      "lamda = lamda*10**-9;      #Wavelength of laser light(m)\n",
+      "d = d*10**-2;      #Diameter of the aperture of source(m)\n",
+      "f = f*10**-2;      #Focal length of the lens(m)\n",
+      "a = d/2;    #Radius of the aperture of source(m)\n",
+      "A = math.pi*lamda**2*f**2/a**2;     #Area of the spot at the focal plane, metre square\n",
+      "I = P/A;     #Intensity at the focus(W/m**2)\n",
+      "I = I/10**7;\n",
+      "I = math.ceil(I*10**4)/10**4;     #rounding off the value of I to 1 decimal\n",
+      "\n",
+      "#Result\n",
+      "print \"The area of the spot at the focal plane is\",A, \"m**2\"\n",
+      "print \"The intensity at the focus is\",I,\"*10**7 W/m**2\""
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "The area of the spot at the focal plane is 1.76714586764e-10 m**2\n",
+        "The intensity at the focus is 2.8295 *10**7 W/m**2\n"
+       ]
+      }
+     ],
+     "prompt_number": 14
+    },
+    {
+     "cell_type": "heading",
+     "level": 2,
+     "metadata": {},
+     "source": [
+      "Example number 11.5, Page number 251"
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "\n",
+      "\n",
+      "#importing modules\n",
+      "import math\n",
+      "from __future__ import division\n",
+      "\n",
+      "#Variable declaration\n",
+      "h = 6.626*10**-34;     #Planck's constant(Js)\n",
+      "c = 3*10**8;     #Speed of light in free space(m/s)\n",
+      "lamda = 1064;    #Wavelength of laser light(nm)\n",
+      "P = 0.8;    #Average power output per laser pulse(W)\n",
+      "dt = 25;    #Pulse width of laser(ms)\n",
+      "\n",
+      "#Calculation\n",
+      "dt = dt*10**-3;       #Pulse width of laser(s)\n",
+      "lamda = lamda*10**-9;     #Wavelength of laser light(m)\n",
+      "E = P*dt;   #Energy released per pulse(J)\n",
+      "E1 = E*10**3;\n",
+      "N = E/(h*c/lamda);    #Number of photons in a pulse\n",
+      "\n",
+      "#Result\n",
+      "print \"The energy released per pulse is\",E1,\"*10**-3 J\"\n",
+      "print \"The number of photons in a pulse is\", N\n"
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "The energy released per pulse is 20.0 *10**-3 J\n",
+        "The number of photons in a pulse is 1.07053023443e+17\n"
+       ]
+      }
+     ],
+     "prompt_number": 17
+    },
+    {
+     "cell_type": "heading",
+     "level": 2,
+     "metadata": {},
+     "source": [
+      "Example number 11.6, Page number 251"
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "\n",
+      "#importing modules\n",
+      "import math\n",
+      "from __future__ import division\n",
+      "\n",
+      "#Variable declaration\n",
+      "lamda = 693;     #Wavelength of laser beam(nm)\n",
+      "D = 3;       #Diameter of laser beam(mm)\n",
+      "d = 300;    #Height of a satellite above the surface of earth(km)\n",
+      "\n",
+      "#Calculation\n",
+      "D = D*10**-3;    #Diameter of laser beam(m)\n",
+      "lamda = lamda*10**-9;     #Wavelength of laser beam(m)\n",
+      "d = d*10**3;     #Height of a satellite above the surface of earth(m)\n",
+      "d_theta = 1.22*lamda/D;    #Angular spread of laser beam(rad)\n",
+      "dtheta = d_theta*10**4;\n",
+      "dtheta = math.ceil(dtheta*10**2)/10**2;     #rounding off the value of dtheta to 2 decimals\n",
+      "a = d_theta*d;      #Diameter of the beam on the satellite(m)\n",
+      "a = math.ceil(a*10)/10;     #rounding off the value of a to 1 decimal\n",
+      "\n",
+      "#Result\n",
+      "print \"The height of a satellite above the surface of earth is\",dtheta,\"*10**-4 rad\"\n",
+      "print \"The diameter of the beam on the satellite is\",a, \"m\"\n"
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "The height of a satellite above the surface of earth is 2.82 *10**-4 rad\n",
+        "The diameter of the beam on the satellite is 84.6 m\n"
+       ]
+      }
+     ],
+     "prompt_number": 25
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [],
+     "language": "python",
+     "metadata": {},
+     "outputs": []
+    }
+   ],
+   "metadata": {}
+  }
+ ]
+}
\ No newline at end of file