William Angerer - Department of Physics and Astronomy - University ...

More documents

Recommendations

Info

191 PMT to photon counter snubber Figure 7.7: Snubber schematic to reduce current pulse ringing. A signal is reflected from the short coaxial cable and reshapes the current pulse from the P:\IT. The length of the cable determines the delay of the reflected pulse and the resistance of the variable resistor determines the magnitude of the reflected signal. We adjusted the variable resistor while observing the current pulse on an oscilloscope to minimize pulse ringing. This figure was adapted from reference [lllJ. a main pulse followed by several smaller pulses. If the height of these secondary oscillations had been above the discriminator level, the pulse was counted twice. By placing a variable resistor at a distance of 6 inches from the PMT and in parallel with the signal cable to the photon counter [lllJ, we introduced electrical feedback into the signal (see Fig. 7.7). This feedback reshaped the pulse and damped the pulse ringing. Hence, we ensured each signal pulse was counted only once. 7.2.3 Registering and Positioning Samples In contrast to second-harmonic generation from a Si wafer, which is homogeneous. many applications of second-harmonic microscopy require accurate and reproducible control of the sample position. Reproducibility and accuracy of the sample position Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
192 depend on two components: a highly accurate translation stage and an optical detection scheme to correlate sample features with the focused Ti:Ah03 beam. Our translation staged consists of a Newport three axis translation stage model 462-XYZ :\II. vVe positioned the stage with a long travel, high resolution, i.e. 0.25 J1.m, ~ewport micrometer model HR-l. The micrometers were attached to computer controlled stepper motors. vVe briefly summarize the unique features of our stepper motors. A more complete description of stepper motors is found in reference [1121. vVe operated our -i-phase stepper motors in the half step mode. This extended the number of steps per rotation from 200 to 400, which corresponds to a minimum step size of 1.25 J1.m. Since our beam size was 3 J1.m, the beam was overlapped with its previous position. Thus, complete scanning of the sample was ensured. During the experiment. we positioned the sample at the focal point of the objective by adjusting the height of the sample to produce a collimated fundamental beam. VVe subsequently made a finer adjustment of the sample height to ma.ximize the SHG signal. Second-harmonic generation microscopy is most useful as a probe of heterogeneous systems. In particular, SHG microscopy enhances the visualization of and provides contrast to heterogeneous systems with similar linear optical properties. In addition, SHG microscopy can distinguish between linear and nonlinear regions. One such system consists of carbon nanotubes and carbon nanoropes deposited on glass. Although carbon nanotubes have symmetries that allow second-harmonic generation. the sam- Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
Page 1 and 2:
SHG SPECTROSCOPY OF GALLIUM NITRIDE
Page 3 and 4:
COPYRIGHT vVilliam E. Angerer 1998
Page 5 and 6:
ACKNOWLEDGEMENTS I am most grateful
Page 7 and 8:
vi and support over the last three
Page 9 and 10:
viii and we report on photoluminesc
Page 11 and 12:
x 2.5 ~ovel Technique and Apparatus
Page 13 and 14:
Xll 7.3 7.2.3 Registering and Posit
Page 15 and 16:
xiv
Page 17 and 18:
xvi 2.10 Device for measuring ultra
Page 19 and 20:
xviii 6.5 Polarization and propagat
Page 21 and 22:
2 scopies as a probe of these featu
Page 23 and 24:
4 tionallinear microscopy is unable
Page 25 and 26:
6 interference by group velocity mi
Page 27 and 28:
Chapter 2 Introduction to Nonlinear
Page 29 and 30:
10 the electric fields as In this t
Page 31 and 32:
12 SHG is a virtual process, Le. th
Page 33 and 34:
14 2.3 (2) Xijk and Symmetry In gen
Page 35 and 36:
16 X (2) zxx = ,\.zyy v(2) (2) = v(
Page 37 and 38:
18 X~}k(W = 2wo) of our GaN samples
Page 39 and 40:
20 nonlinear element of quartz, X~~
Page 41 and 42:
22 the transmitted wave, E:t'°, Th
Page 43 and 44:
24 150 I I "1 I :) ~ >- -. iii c v
Page 45 and 46:
26 Quartz fundamental Figure 2.5: I
Page 47 and 48:
28 The bound wave, which propagates
Page 49 and 50:
30 1/e 2 its ma.'{imum value. This
Page 51 and 52:
32 Here, x~;!Aw = 2wo) is a constan
Page 53 and 54:
34 simplifications (2.39) and (2.40
Page 55 and 56:
36 nonlinear waves. This model assu
Page 57 and 58:
38 Fourier transform to E /2 (r, w)
Page 59 and 60:
40 3 mm and with the parameters dis
Page 61 and 62:
42 I " i iii iii iii iii iii iii ii
Page 63 and 64:
44 parameter value Bl 2.35728 B2 -0
Page 65 and 66:
46 is measured as a function of tra
Page 67 and 68:
48 send pulse into device \11 input
Page 69 and 70:
50 2.6 Conclusion In this brief sec
Page 71 and 72:
52 LOCK-IN AMPLIAER LOCK-IN AMPLIAE
Page 73 and 74:
54 After polarization, the beam was
Page 75 and 76:
56 PO HR !l o IV team BP Figure 3.3
Page 77 and 78:
58 .. ........... • / ~ '" ~ r --
Page 79 and 80:
60 The production of ultrafast, hig
Page 81 and 82:
62 800 ~ 0 0 J 0 0 0 0 J ~ 0 600~ 0
Page 83 and 84:
64 measurements. Typically, I incre
Page 85 and 86:
66 described below. Note that laser
Page 87 and 88:
68 sentiallya nonlinear optical int
Page 89 and 90:
70 780 800 820 840 860 880 900 920
Page 91 and 92:
72 Unlike the linear spectroscopic
Page 93 and 94:
74 fore, the ratio of these two qua
Page 95 and 96:
76 of :UN is deposited on the Ah03
Page 97 and 98:
78 computer HeNe Las polarizer chop
Page 99 and 100:
80 ~------".... GaN A12a3 index flu
Page 101 and 102:
82 + d I , GaN A12a3 Figure 4.3: Co
Page 103 and 104:
84 4.2 Measurement of Indices of Re
Page 105 and 106:
86 fields at the lh interface to th
Page 107 and 108:
88 traveling wave, i.e. (-1.7) wher
Page 109 and 110:
90 Note that the additional subscri
Page 111 and 112:
92 £b, are defined only at the int
Page 113 and 114:
94 Equations (4.30) and (4.32) are
Page 115 and 116:
96 the calculation of the transmitt
Page 117 and 118:
98 '- -0 OJ N 0.4 o E ~ o Z 0.2 o 2
Page 119 and 120:
100 2.0 "'"" "I 1.5 E ::t ~ --c 0 -
Page 121 and 122:
102 4.3 Photoluminescence of GaN To
Page 123 and 124:
104 a photoluminescence measurement
Page 125 and 126:
106 :J 0.01 0 ~ L ~ 0.008 r- :n :v
Page 127 and 128:
108 0.08 ~. j -i ,-... I I ""I :::l
Page 129 and 130:
Chapter 5 Properties of GaN In rece
Page 131 and 132:
112 5.1 Crystal Structure :\ crucia
Page 133 and 134:
114 PJO'tI [{fall Figure 5.1: \Vurz
Page 135 and 136:
116 e 4 r .1 It Figure 5.2: Calcula
Page 137 and 138:
118 Parameter Symbol Value electron
Page 139 and 140:
120 high intrinsic electron concent
Page 141 and 142:
122 equation (5.2), is represented
Page 143 and 144:
124 C6v E E £l. 2C3 2C 3 2C6 2C 6
Page 145 and 146:
126 gap, the nonlinear susceptibili
Page 147 and 148:
128 rrb 10.0 eV -------- 5 9.0 eV r
Page 149 and 150:
130 In> 1m> 1m>
Page 151 and 152:
132 Emission of a photon on the bra
Page 153 and 154:
134 5.5 MOCVD Growth of GaN Our GaN
Page 155 and 156:
136 # dopant thickness mobility car
Page 157 and 158:
138 6.1 Nonlinear Optical Spectrosc
Page 159 and 160: 140 y lab X)lSlaJ / 2m Figure 6.1:
Page 161 and 162: 142 Fig. 6.2 displays the azimuthal
Page 163 and 164: 144 includes the effects of pulse p
Page 165 and 166: 146 6.3 Theory of Nonlinear Optical
Page 167 and 168: 148 L x i d 1 E( 00) air GaN sapphi
Page 169 and 170: 150 wavevector components. The free
Page 171 and 172: 152 z y x E( ro) air GaN Figure 6.5
Page 173 and 174: 154 various free waves and summing
Page 175 and 176: 156 factors are: the nonlinearity o
Page 177 and 178: 158 where v /2 is the group velocit
Page 179 and 180: 160 i N -' '- 0 ::J a 0 o.sf fiftH!
Page 181 and 182: 162 4 ""' ::J en Q) - -' .D 2L ·oJ
Page 183 and 184: 164 approximation. The agreement be
Page 185 and 186: 166 midgap state) could playa role
Page 187 and 188: 168 r: b S ~ r b I rs ~ r b I 0)1 r
Page 189 and 190: 170 in various bonding geometries w
Page 191 and 192: , 172 .----. ::l U'J Q) ttl 0 '-.,;
Page 193 and 194: Chapter 7 SHG Microscopy The majori
Page 195 and 196: 176 7.1 Historical Context of Secon
Page 197 and 198: 178 comPJter - - - - - - - - - ~ ,-
Page 199 and 200: 180 second-harmonic light towards t
Page 201 and 202: 182 ~ 20 _____ ~ ____ J -----f- ---
Page 203 and 204: 184 wave at normal incidence is (7.
Page 205 and 206: 186 polarization is negligible for
Page 207 and 208: chopper AGate B Gate Signal Figure
Page 209: 190 E 4000 1 c: 0 3000 ~ rJl -' 0 c
Page 213 and 214: 194 nanorope ~ Figure 7.8: Carbon n
Page 215 and 216: 196 of light reflected from the sam
Page 217 and 218: 198 mean square deviation, of the p
Page 219 and 220: 200 7.3 Calculated SHG Signal from
Page 221 and 222: 202 parameter symbol value laser re
Page 223 and 224: 204 parameter symbol value surface
Page 225 and 226: Chapter 8 Conclusion In this brief
Page 227 and 228: 208 properties of carbon nanotubes.
Page 229 and 230: 210 that propagate through quartz a
Page 231 and 232: Appendix B Theory of Nonlinear Resp
Page 233 and 234: 214 Fourier transforming equation (
Page 235 and 236: 216 and (CA) with f.b == t(.:.vo) a
Page 237 and 238: 218 The polarization, et, of the po
Page 239 and 240: 220 and (0.1.,1) respectively. Equa
Page 241 and 242: Appendix E Effect of Sapphire Miscu
Page 243 and 244: 224 with cosO 0 - sin (} o 1 o (E.3
Page 245 and 246: 226 Let us compare the light transm
Page 247 and 248: 228 , .............................
Page 249 and 250: 230 it ( (fp·top..,(arr (ll, M r "
Page 251 and 252: 232 nal-2.00 tab'(:r[ihi]-:r[ila] )
Page 253 and 254: 234 1 - 2500.0; III - xU]; 1/ ti. t
Page 255 and 256: Bibliography [1] R. K. Chang~ J. Du
Page 257 and 258: 238 [12] J. QL "V. Angerer, M. S. Y
Page 259 and 260: 240 Diamond, SiC and Wide Bandgap S
Page 261 and 262:
242 [40] M. M. Choy and R. L. Byer,
Page 263 and 264:
244 [55] \V. P. Lin, P. M. Lundquis
Page 265 and 266:
246 [70] J. vV. Yang, J. N. Kunzia,
Page 267 and 268:
248 [85] B. Monemar and O. Lagerste
Page 269 and 270:
250 [99] R. C. Miller, Optical Seco
Page 271 and 272:
252 [114] "V. de HeeL W. S. Bacsa,
show all

William Angerer - Department of Physics and Astronomy - University ...

Create successful ePaper yourself

Delete template?

Save as template?