FOREWORD ....................................................... 11
ACKNOWLEDGEMENTS ............................................... 14
ACRONYMS AND ABBREVIATIONS ..................................... 15
PART I METHODOLOGIES AND TECHNIQUES ............................ 39
1 Introduction ................................................ 39
2 Single alkali earth fluorides ............................... 42
2.1 Properties and applications ............................ 42
2.1.1 Calcium fluoride ................................ 42
2.1.2 Application in Vapour Lasers Optics ............. 43
2.1.3 Application as host laser materials ............. 44
2.2 Review of growing techniques ........................... 50
2.2.1 Growth of large diameter boules ................. 55
2.2.2 Growth in Reactive Atmosphere ................... 64
2.3 Crystal characterization ............................... 65
2.4 Optical processing (Working the crystals) .............. 77
2.4.1 Specification of optical windows/flat mirrors
of CaF2 ......................................... 80
2.5 Standardization and crystal grades specification ....... 80
2.5.1 Categorization and grading (classification) of
optical fluorite: characteristic parameters ..... 84
2.6 Calcium fluoride yield prognosis ....................... 90
3 Multi-component fluoride systems ............................ 92
3.1 Mixed alkali earth fluoride systems .................... 94
3.2 Doped mixed alkali earth fluoride systems .............. 95
3.3 Single and in-batch growth of CaF2-SrF2 solid
solutions .............................................. 97
4 Factors influencing the crystal growth ...................... 99
4.1 Oxygen contamination: sources and methods for
removing ............................................... 99
4.2 Impurities in Natural Fluorite: methods for
determination ......................................... 101
4.3 Melt Supercooling: criterion for interface stability .. 103
4.3.1 Melt Supercooling as physical-chemical
phenomenon ..................................... 103
4.3.2 Criteria for interface stability:
constitutional supercooling principle .......... 105
4.3.3 Function of stability and interdiffusion
coefficient .................................... 108
4.3.4 Perturbation theory of interface stability ..... 109
4.3.5 Normal growth criterion ........................ 111
4.3.6 Function of stability and properties of mixed
fluoride systems ............................... 111
4.3.6.1 Mixed alkali earth fluoride systems ... 111
4.3.6.2 Mixed alkali earth - rare earth
fluoride systems ...................... 113
4.4 Speed of crucible withdrawal .......................... 114
4.5 Temperature head and melt vaporization ................ 115
4.5.1 Vaporization Mechanisms ........................ 117
5 Fundaments of Purification/Growing Techniques .............. 119
6 Thermodynamic grounded characteristics for RE
purification ............................................... 121
7 RE Purification processes: mass-transport and kinetics ..... 125
7.1 Differential equations for gas-vapour mass-transport .. 125
7.1.1 Quasi-Equilibrium: Distribution of Gas-Vapour
Constituents ................................... 125
7.1.2 Assumptions for Analytical Solution ............ 128
7.1.3 Solution in case of stationary vapour flux ..... 129
7.2 Effective gas-conductivities in lids' channels: end
effects ............................................... 130
7.3 Total pressure distribution along the channels ........ 134
7.4 Gas-conductivity as a function of geometric factor .... 134
7.5 Mass-transport at dominance of Knudsen diffusion ...... 135
7.6 Distribution of inert gaseous species ................. 135
7.7 Total Pressure in specialized crucible: influence of
the vacuum system ..................................... 136
7.8 Deposit in the common crucible compartment ............ 138
8 Methodologies and technical equipment ...................... 139
8.1 Preparation of deeply purified CaF2 precursors ........ 139
8.1.1 Preparation of grained starting fraction ....... 145
8.1.2 Chemical purification .......................... 147
8.1.3 Removal of oxygen contaminants (ROXC)........... 148
8.1.4 Removal of the embedded RE impurities (RREI) ... 149
8.1.5 Control of impurities content .................. 150
8.2 Crystal Growth approach and used technical means ...... 152
8.3 Localization of the position for growth interface ..... 156
8.4 Determination of the axial temperature profile ........ 160
8.5 Crystal characterization .............................. 161
8.5.1 Spectrophotometric analysis: optical
criterion for crystal quality .................. 161
8.5.2 Vapour laser Irradiation Technique ............. 166
8.5.3 Optical homogeneity, birefringence,
fluorescence ................................... 168
8.5.4 Stoichiometric uniformity in calcium
strontium fluorides ............................ 169
8.6 Laser damage characteristics .......................... 171
PART II GROWTH OF SINGLE CALCIUM FLUORIDE .................... 172
9 Experimental - results and discussion ...................... 172
9.1 PbF2 scavenger efficiency without HTP of fluorspar .... 172
9.2 Residual partial pressures and crystal-chemical
reactions ............................................. 174
9.3 Scavenger efficiency of PbF2 and ZnF2 after HTP of
starting fluorspar .................................... 176
9.4 Controllable removal of RE impurities via High-T
Purification Technique ................................ 179
9.4.1 Gaseous-vapour mass transport in conventional
multicameral crucible .......................... 179
9.4.1.1 Vapour flux versus total gas-
conductivity and temperature head ..... 179
9.4.1.2 Total pressure versus total gas-
conductivity .......................... 181
9.4.1.3 Back diffusion of chemically inert
species ............................... 183
9.4.2 Mass-transport and kinetics in specialized
multicameral crucible .......................... 186
9.4.2.1 Vapour flux throughout lids'
channels versus geometric factor ...... 186
9.4.3 Degree of RE purification for particular RE .... 187
9.4.4 Purification deepness and intensiveness for
fluorspars with largely varying impurities'
content ........................................ 188
9.4.5 Dependence of the deepness for
Ce-purification on apparatus factors ........... 192
9.4.6 Deposition control via adjusting the vapour
pressure inside the crucible ................... 194
9.4.7 Influence of "substance" factors on cerium
purification ................................... 198
9.4.7.1 Distribution of Ce under segregation
mechanism ............................. 199
9.4.7.2 Counter-directional mass-transfer
for presented REs ..................... 202
9.4.8 Kinetic limitations during RE purification/
growing processes .............................. 207
9.5 Combined spectrophotometric and analytical methods .... 208
9.5.1 Experimental ................................... 208
9.5.2 Discussion ..................................... 210
9.5.2.1 AAS measurements ...................... 210
9.5.2.2 Iron distribution ..................... 211
9.5.2.3 Zinc and copper distribution .......... 212
9.5.2.4 Lead distribution ..................... 213
9.5.2.5 Light-scattering effect ............... 216
9.5.2.6 Rare earth elements distribution ...... 216
9.5.2.7 UV-grade crystals ..................... 217
9.5.3 Conclusions .................................... 218
10 Single CaF2 crystal growth: interface stability ............ 219
10.1 Effect of oxygen-containing contaminants .............. 219
10.2 Control of the shape and position of growth
interface ............................................. 221
10.2.1 Axial Temperature Distribution in Empty
Crucible (ATDEC) ............................... 221
10.2.2 Location and shape at quenching the load ....... 222
10.2.3 Influence of position and design of crucibles
on QI location ................................. 224
10.2.4 Convexity of QI-shape .......................... 225
10.2.5 Verification by crystal growth runs ............ 226
10.3 Determination and control of crystallization
isotherm shift ........................................ 228
10.4 Optical properties of growing crystals ................ 231
11 Controllable growing conditions for structural perfection .. 232
11.1 Structural defects and light-extinction losses ........ 232
11.2 Stress induced birefringence .......................... 235
11.3 Total losses of transmitted monochromatic laser
beam .................................................. 238
11.3.1 Experimental setup ............................. 238
11.3.2 Results and discussion ......................... 239
11.3.3 Followings ..................................... 243
11.4 Overall conclusion .................................... 244
12 Laser damage characteristics of the grown CaF2 ............. 245
PART III LARGE-SIZE CRYSTALS: PECULIARITIES ................... 248
13 Large size CaF2 crystals ................................... 248
13.1 Target growing experiments ............................ 248
13.1.1 Experimental runs: results ..................... 248
13.1.1.1 Two-zones growth with moderate rate
(run El) .............................. 248
13.1.1.2 Single-zone growth with slow rate
(run E2) .............................. 259
13.2 Guiding laboratory experiments ........................ 263
13.2.1 Boules' characterization ....................... 269
13.2.2 Effect of OAC .................................. 271
13.3 Optimizing laboratory experiments ..................... 271
13.3.1 Loss of starting material ...................... 272
13.3.2 Crust formation ................................ 272
13.3.3 Saturation pressure ............................ 272
13.3.4 Residual pressure into the chamber ............. 275
13.3.5 Shape and micro-relief of the upper boules'
surface ........................................ 275
13.3.6 Coloration ..................................... 275
13.3.7 Inclusions and mosaics ......................... 276
13.3.8 Extinction index ............................... 276
13.4 Conclusion ............................................ 276
PART IV MODELS FOR GROWING CONTROL ............................ 278
14 Model investigations: thermal field flows effects upon
the growth ................................................. 278
14.1 Thermal conditions at nucleation ...................... 278
14.2 Thermal conditions during the growing ................. 283
14.3 Radial thermal inhomogeneities ........................ 288
14.4 Models' conclusion .................................... 295
15 Thermal convections ........................................ 297
15.1 Followings ............................................ 304
PART V GROWTH OF CaF2-SrF2 SOLID SOLUTION CRYSTAL SYSTEM ... 305
16 Experimental results and discussion ........................ 305
16.1 Runs conditions and grown boules ...................... 305
16.2 Stoichiometry control ................................. 308
16.3 Optical quality of the grown boules ................... 311
16.4 Control on the shape and position of growth
interface ............................................. 315
16.5 Interface stability during the growth of Ca1-xSrxF2
crystals .............................................. 316
16.5.1 Specification of the phase diagram ............. 316
16.5.2 Normal growth criterion ........................ 318
16.5.3 Equilibrium coefficient of segregation ......... 320
16.5.4 Compositional dependence of stability
function ....................................... 321
16.5.5 Determination of the real axial T-gradient
into the load .................................. 323
16.5.6 Real crystallization rate determination ........ 327
16.5.7 Interdiffusion coefficient determination ....... 328
16.5.8 Stability criterion and crystal quality ........ 329
16.5.9 Critical melt temperature gradient ............. 332
16.5.10 Followings .................................... 337
PART VI FLUORITE LATTICE MODELLING ............................ 339
17 Structural and optical properties of crystals grown from
"cerium" type of fluorspar ................................. 339
17.1 Theoretical considerations and experimental ........... 339
17.2 Crystal structure ..................................... 340
17.3 Optical properties .................................... 343
17.3.1 Spectral dependence of optical absorption
coefficient .................................... 343
17.3.2 x-dependence of the position of Ce3+-
absorption band near 306 nm .................... 344
17.3.3 x-dependencies of 306 nm Ce3+-absorption peak
intensity and width ............................ 345
17.3.4 Relationships between structural, chemical
and optical parameters ......................... 346
17.4 Structural conclusions ................................ 348
PART VII CONCLUSIONS .......................................... 349
REFERENCES .................................................... 352
Оптични флуориди: пречистване и израстване на кристалл,
приложимост и перспективи (Summary) ........................... 377
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