CHEM01200604009 Sreejith Kaniyankandy - Homi Bhabha ...

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77 Grating Output Input Mirror Grating Figure 2.10. Schematic of a typical compressor. The compressor consists of pair of gratings placed parallel to achieve negative dispersion. The negative dispersion delays the red part of spectrum compared to blue. The compressed pulse has duration of 50fs. Since the amplified pulse has a very high peak power this pulse can be exploited to exhibit nonlinearity, which in turn is useful in second harmonic and white light generation. The compressed pulse has energy of 1.13W with wavelength centered at 800nm. This pulse is used to generate 400nm pump and white light ranging from 450nm-1100nm used as the probe for our studies. 2. 8. 3. Second Harmonic Generation-400nm Pump The second harmonic generation of 800nm output of Ti-S amplifier system is accomplished by using β-barium borate (BBO). The induced dielectric polarization in a material in presence of electric field of light is given by P( E E E ...) (2.15) (1) (2) 2 (3) 3 0 0 0
78 Here E is the electric field of light, ( n) is the susceptibility of nth nonlinearity and magnitude decreases for the higher nth order terms. Therefore it is clear from the equation that harmonic generation is present only when light intensities are very high. For many crystals used for SHG is seen for light intensities of the order of GW/cm 2 .The second term in the equation is responsible for second harmonic generation. Let’s consider the second order term P (2) 2 2 0 E (2.16) For an electromagnetic wave E E0 cos( t kr) , (2) 2 2 1 (2) 2 (2) 2 P2 0 E0 cos ( tkr) ( 0 E0 0 E0 cos 2( t kr)) (2.17) 2 Additionally harmonic is generated only if the phases of the two waves match. This condition is given by k( ) k(2 ) . This condition is satisfied in uniaxial birefringent crystals like BBO that have two different refractive indices n o and n e for the ordinary and the extraordinary waves where n (2 , ) n ( ) . In our set up we use pulse energy of e o ~100μJ/pulse at 800nm which is focused on 0.5mm BBO crystal to generate ~10μJ/pulse of second harmonic at 400nm. 2. 8. 4. White Light Generation- 450-1100nm Probe To monitor transients after a pump pulse excitation, we use a probe pulse with wavelengths ranging from visible to near IR region. This is done by creating white light using a part of 800nm amplified output. The phenomenon responsible for generation of white light is self phase modulation. The 800nm pulse with time duration of 50fs and energy of few
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Charge Transfer Dynamics in Quantum
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DECLARATION I, hereby declare that
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ACKNOWLEDGEMENTS It is my privilege
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1.3.5. Defect Mediated Relaxation 2
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2. 8. 4. White Light Generation- 45
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6.2. Experimental 6.2.1.Synthesis o
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devices based on QDs it has been sh
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Furthermore generation of pump (~40
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shell). This clearly indicated that
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12. V. I. Klimov, J. Phys. Chem. B,
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1.13 Reactant and Product Potential
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light. Inset: Kinetic traces monito
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6.5 Transient decay kinetics of gra
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at 670 nm after exciting at 400 nm
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ABBREVIATIONS BET BQ CB CCD CdS CdT
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1 Chapter 1
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3 size dependent optical properties
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5 1.2. Physics of Semiconductors 1.
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7 As seen from the schematic, poten
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9 Substituting this in Schrödinger
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11 ( r, r ) ( r ) ( r ) (1.13) e
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13 E E E 2 2 2 EX ne, le nh,
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15 spherical symmetry of field. The
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17 gE ( ) 2Em 2 3 3 (1.25) For a
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19 1.3.2. Electron-Hole energy tran
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21 Impact Ionization Figure 1.7. Sc
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23 understanding on mechanistic asp
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25 carriers are unable to sample th
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27 CB VB QD Metal Figure. 1. 10. Sc
Page 68 and 69: 29 energy barrier. Therefore it is
Page 70 and 71: 31 1 f q 2 A qB (1.30) 2 In equa
Page 72 and 73: 33 Vibrational contribution can be
Page 74 and 75: 35 1. 7. 1. Electron Injection ET i
Page 76 and 77: 37 Under assumption of invariance o
Page 78 and 79: 39 distribution. To achieve good si
Page 80 and 81: 41 initially achieved monodispersit
Page 82 and 83: 43 and rate of charge transfer acro
Page 84 and 85: 45 1.32 P. V. Kamat, J. Phys. Chem.
Page 87: 47 Chapter 2
Page 90 and 91: 49 chemical species. Since a partic
Page 92 and 93: 51 fluorescence forms an important
Page 94 and 95: 53 eliminated by use of standard wh
Page 96 and 97: 55 sample. Raman spectroscopy is ba
Page 98 and 99: 57 will appear bright and region wi
Page 100 and 101: 59 volatile solvent is drop casted
Page 102 and 103: 61 spots arise from diffraction fro
Page 104 and 105: 63 The electrical signal is then ch
Page 106 and 107: 65 delayed and inverted. The two si
Page 108 and 109: 67 Pump-probe technique is one of t
Page 110 and 111: 69 Amplifier Jade Stretcher fs Osci
Page 112 and 113: 71 Figure 2.6. Optical layout of Ti
Page 114 and 115: 73 Grating Convex Mirror Concave Mi
Page 116 and 117: 75 changes the polarization from ho
Page 120 and 121: 79 μJ has a very high peak power.
Page 122 and 123: 81 2.6. Dynamical Theory of X-Ray D
Page 128 and 129: 85 Therefore the study of interfaci
Page 130 and 131: 87 3. 2. Experimental Section 3.2.1
Page 132 and 133: 89 and intensity show absence of ot
Page 134 and 135: 91 which is also neutral; therefore
Page 136 and 137: 93 electron transfer times. This re
Page 138 and 139: 95 r B a * 0 3.1 me / me Now the
Page 140 and 141: 97 nonadiabatic case the electron t
Page 142 and 143: 99 drastically reduced leading to a
Page 144 and 145: 101 While the study of injection dy
Page 146 and 147: 103 study. Based on the injection d
Page 148 and 149: 105 17. L. E. Brus, J. Phys. Chem.
Page 154 and 155: 109 of the QDs. As a result surface
Page 156 and 157: 111 4.2.2. Synthesis: The CdTe QDs
Page 158 and 159: 113 lower hole state. In CdSe the l
Page 160 and 161: 115 4.2 inset. The kinetic traces a
Page 162 and 163: 117 growth of the bleach kinetics (
Page 164 and 165: 119 previous section we have discus
Page 166 and 167: 121 lived charge transfer complex w
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123 100 times concentration of the
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125 4.5. References 4.1. Efros, Al.
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127 Chapter 5
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129 been made in the synthesis of t
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131 metallic synthesis by arrested
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133 5.3. Result and discussion: 5.3
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135 indicating a confinement induce
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137 absorption studies that on form
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139 1000 c b PL Intensity 100 10 a
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141 samples due to a very weak exci
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143 dynamical spectrum is negligibl
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145 Earlier authors [5.4] reported
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147 Sample t r(ps) t 1(ps) t 2(ps)
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149 In addition to the cooling dyna
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151 pulse-width time scale followed
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153 5.20. Sreejith Kaniyankandy, Sa
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155 CHAPTER 6 Charge Separation in
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157 Studies by Wang et. al. [6.15]
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159 graphene in a 1M NaOH solution.
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161 Intensity (a.u.) 5 4 3 2 1 CdTe
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163 dynamics of graphene oxide and
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165 GO as shown in the Figure 3 rev
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167 electron acceptor for Graphene.
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169 governs the recombination dynam
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171 Sample τ 1 (ps) τ 2 (ps) τ 3
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173 A (mO.D) 10.0 0.0 -10.0 -20.0 0
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175 involved in the relaxation may
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177 Electron quencher (benzoquinone
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179 Scheme 6.1. Schematic of Electr
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181 6.6. Reina, A.; Jia, X.; Ho, J.
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183 6.26. Kaiser, A. B.; Navarro, C
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185 assigned to injection into diff
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187 transfer from CdSe core to ZnTe
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189 However the position of bands i
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