Transition metal and rare earth doped stoichiometric lithium niobate crystals for holographic recording

TRANSITION METAL AND RARE EARTH DOPED STOICHIOMETRIC LITHIUM NIOBATE CRYSTALS FOR HOLOGRAPHIC RECORDING SANJEEV SOLANKI NATIONAL UNIVERSITY OF SINGAPORE 2004 TRANSITION METAL AND RARE EARTH DOPED STOICHIOMETRIC LITHIUM NIOBATE CRYSTALS FOR HOLOGRAPHIC RECORDING SANJEEV SOLANKI (M.Tech) A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY DEPARTMENT OF ELECTRICAL & COMPUTER ENGINEERING NATIONAL UNIVERSITY OF SINGAPORE 2004 Acknowledgements First and foremost, I would like to thank my Ph.D. supervisors Prof. Chong Tow Chong (Department of Electrical and Computer Engineering, National university of Singapore & Data Storage Institute, Singapore) and Dr Xu XueWu (Data Storage Institute, Singapore), whose breadth of knowledge, outstanding communication skills and organizational ability assured this project’s clarity and completeness. In particular, thanks to Dr Xu Xuewu, who first introduced me to the holographic recording material growth methods and constant wake my interest in the fundamental research. In these years, their brilliance and wise counsel; their unique insights and perspectives and noteworthy talents and dedication, accompany me throughout the program. I would like to thank a number of people: Dr Liang Xinan for constant discussions and also for crystal sample etching and provide the single domain data for as grown crystals. My Yongsoon Tay for polishing crystal samples and Dr Xuwei on providing vertical temperature gradient data of growth furnace. Thanks are also due to Mr Yuan Shaoning for his contribution in developing various experimental setups. Finally, I would like to convey deep appreciation for my wife for her endless support for all these years. She has been a constant support and encouragement. I dedicate this thesis to her and all my teachers. i Summary We used TSSG (top seeded solution growth method) to grow undoped and doped SLN crystal samples at very low vertical temperature gradient. We thoroughly studied the effect of coherent laser beams on doped SLN crystals and finally performed high speed and high density holographic recording. Developed low vertical temperature gradient flux growth method to grow high quality undoped and doped stoichiometric lithium niobate crystals. Growth was performed mainly along two directions. One was the normal to the facet (012), (1-12), or (-102). The other one was perpendicular to both the normal to the facet and X axis Crystal samples of 300 mm in height and 18 mm in diameter were obtained by this method. Optical characterization method was used to confirm the stoichiometric composition of undoped as well as doped (Fe,Mn,Tb) SLN crystals. The shift in OH-1 vibration peak supported the stoichiometric composition of doped crystals. Furthermore the non existence of a Raman peak at 740 cm-1 confirmed the non- existence of antisite intrinsic defect even in highly doped SLN crystals. Beam fanning in doped SLN crystals was found to be deterministic compared to doped CLN crystals, which showed random beam fanning. The backward fanning in Z – cut crystals was relatively weak in Tb containing SLN crystals and the transmitted beam spot always preserved its shape. But for doped CLN crystal the transmitted beam spot was highly distorted. Further Z – cut SLN crystals were able to sustain very high incident power density of ~150kW/cm2. ii Plane wave hologram recording with increasing power densities was performed in doped SLN crystals. Total recording time ~1sec was obtained at total recording power density of 70W/cm2. Ultra high speed image recording was performed at total recording power density of ~81kW/cm2 and the image was successfully retrieved for recording time of ~1msec, which was 2-3 order faster than previously reported hologram recording time. For example Burr et al. reported average recording time per hologram of ~0.34 sec [86] and Mok et. al. ~1 sec [24,33]. Shift –multiplexing method was implemented using focused signal beam and diverging reference beam to store matrix of X holograms. Holograms were recorded with in-plane shift of 100 µm and out-of plane shift of 300 µm, which is similar to the results reported for recording with diverging/converging signal beam [120]. At the IR (778 nm) recording and UV (365 nm) gating, SLN crystal samples with low Tb doping concentration showed better performance from non-volatility point of view, i.e. readout of recorded hologram resulted in slow erasing of recorded hologram. The erasing time constant of recorded hologram was ~5 times slower in SLN crystal with ppm Tb than in SLN with 140 ppm Tb. iii Contents Acknowledgements i Summary ii Contents iv List of Tables viii List of Figures . ix 1. INTRODUCTION 1.1. Photorefractive (PR) effect 1.2. Theory – PR in crystals . 1.3. Applications . 1.4. Media for holographic recording 1.5. Stoichiometric lithium niobate 1.6. Thesis overview . 2. Crystal Growth 11 2.1 Introduction . 11 2.2 Growth of undoped and doped SLN crystals 12 2.2.1 Stoichiometric undoped . 12 2.2.2 Stoichiometric doped . 19 2.2.3 Stoichiometric doubly doped 20 2.2.3 Stoichiometric triply doped . 20 iv 2.3 Morphology . 21 2.3.1 Crystal structure and effect of growth direction 21 2.4 XRD Analysis 26 2.4.1 Powder XRD 26 2.3.2 Crystal Orientation . 28 2.3.3 Summary . 31 Appendix2.1 . 32 3. Optical Characterization 34 3.1 Introduction . 34 3.2 Absorption spectra 35 3.2.1 Absorption edge 35 3.2.2 Effect of doping and annealing on absorption edge . 40 3.2.3 Effect of doping and annealing on Optical Spectra 41 3.3 OH-1 spectra . 45 3.3.1 Stoichiometric composition 45 3.3.2 Effect of doping 46 3.4 Raman spectra . 48 3.4.1 Theory . 48 3.4.2 Effect of stoichiometry . 49 3.4.3 Summary . 54 4. Beam Fanning . 55 4.1 Introduction . 55 v 4.2 Backward Beam Fanning – Two-wave mixing 56 4.2.1 Theory – (dynamic & steady state) 56 4.2.2 Experiments and results – Z- Cut Fe:SLN . 62 4.2.3 Experiments and results – Z- Cut Fe:Tb:SLN 70 4.3 Transverse Beam Fanning 78 4.3.1 Theory – (steady state) 78 4.3.2 Experiments and results – X- Cut Fe:SLN . 79 4.3.3 Experiments and results – X- Cut Fe:Tb:SLN 85 4.3.4 Summary . 87 5. One – Color Holographic Recording 89 5.1. Introduction . 89 5.2. One – color theory . 91 5.3. Effect of Non-Reciprocal energy Transfer on diffraction efficiency 94 5.4. Experiments and results 103 5.4.1. Hologram recording with green light (~1W/cm2) 103 5.4.2. Sensitivity and M/# 106 5.4.3. Hologram recording with IR light 109 5.5. High speed recording 110 5.5.1. Plane – wave Recording 110 5.5.2. Image Recording . 120 5.5.3. Shift Multiplexing . 123 5.5.4. Summary . 129 vi 6. Two – Color Holographic Recording 130 6.1. Introduction . 130 6.2. Two – color theory . 131 6.3. Experiments and results 135 6.3.1. Hologram recording UV gating and green recording light 135 6.3.2. Hologram recording UV gating and IR recording light . 141 6.3.3. Summary . 148 7. Conclusion 149 Bibliography . 152 Journal papers . 168 International Conference papers 169 vii List of Tables Table 2.1. Interplanner angles between crystallographic planes. Table 2.2. X Ray Diffraction angle from X,Y,Z and facet planes. Table.2.3. The dnh,nk,nl calculated with the above cell parameters and extinction condition are listed. Table 3.1. 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Sanjeev Solanki, Xuewu Xu, Chong Tow-Chong, “Effect of non-reciprocal energy transfer on diffraction efficiency of reflection hologram in Fe:SLN crystal”, submitted to Josa B. 4. X.W. Xu, T.C. Chong, S. Solanki, X.A. Liang, S.N. Yuan, “Anisotropic thermal expansion of stoichiometric lithium niobate crystals grown along the normal direction of facets”, Optical Materials, Vol. 26, pp.489-494, 2004. 5. Xuewu Xu, Xinan Liang, Tow-Chong Chong, Shaoning Yuan, Sanjeev Solanki, Yongsoon Tay, “Vertical Bridgman growth and optical characterization of LiNbO3:Cu:Ce crystals ” J. Crystal Growth, Vol. 275, pp.e791-e797, 2005. 168 International Conference papers 1. S. Solanki, T.C. Chong, X.W. Xu , “Flux growth and morphology study of stoichiometric lithium niobate crystals”, The Forteenth American Conference on Crystal Growth & Epitaxy, Seattle/USA, 2002, oral presentation. 2. S. Solanki, T.C. Chong, X.W. Xu, Y.S. Tay, “Optical characterization of undoped and doped SLN crystals grown by TSSG method”, The Fifteenth American Conference on Crystal Growth & Epitaxy held jointly with The 11th Biennial (US) Workshop on OMVPE and The 3rd International Symposium on Laser and NLO Materials, Keystone/Colorado/USA, 2003, oral presentation. 3. X.W. Xu, T.C. Chong, S. Solanki, X.A. Liang, S.N. Yuan, “Anisotropic thermal expansion of stoichiometric lithium niobate crystals grown along the normal direction of facets”, The Fifteenth American Conference on Crystal Growth & Epitaxy held jointly with The 11th Biennial (US) Workshop on OMVPE and The 3rd International Symposium on Laser and NLO Materials, Keystone/Colorado/USA, 2003, oral presentation. 4. Xuewu Xu, Xinan Liang, Tow-Chong Chong, Shaoning Yuan, Sanjeev Solanki, Yongsoon Tay, “Vertical Bridgman growth and optical characterization of LiNbO3:Cu:Ce crystals”, The Fourteenth International Conference On Crystal Growth in conjugation with The Twelfth International Conference On Vapor Growth And Epitaxy, Alpes Congres, Grenoble, France . 169 [...]... Experimental setup for high speed plane wave holographic recording Fig.5.16 Recording and erasing curve for Z-cut Fe:Tb:SLN-1 at Irecording = 0.35 W/cm2 Fig.5.17 Recording and erasing curve for Z-cut Fe:Tb:SLN-1 at Irecording = 8.08 W/cm2 Fig.5.18 Recording and erasing curve for Z-cut Fe:Tb:SLN-1 at Irecording = 17.06 W/cm2 Fig.5.19 Recording and erasing curve for Z-cut Fe:Tb:SLN-1 at Irecording = 70.03... melts or form K2O containing melts With reduced intrinsic defects the LN crystals can be made photorefractive by selectively doping with single or multiple transition metal or rare earth elements The electro-optic properties of stoichiometric crystals are improved and as grown 8 crystals are single domain Fe, Mn and Tb are one of the most important dopants for holographic recording Beam fanning and optical... melt and very high vertical temperature gradient (200 – 700 oC) to grow bulk optical quality crystals M.Lee and Kitamura et al [69 – 73, 75 – 76, 78 – 79, 81, 87 – 88, 97, 99 97] has done remarkable work in growth and photorefractive testing of stoichiometric lithium niobate crystal and still continuing to test various doped SLN 7 (stoichiometric lithium niobate) crystals Out of the long list of transition. .. for using low power to recording holograms that slows down the information recording process in X,Y or 45o cut lithium niobate crystals By using Z – cut crystals and low doping concentration, the beam fanning can be drastically reduced and high light power density can be used to faster recording of information carrying holograms Chapter 2 describes the TSSG (Top Seeded Solution Growth) of undoped and. .. Solution Growth) of undoped and doped stoichiometric lithium niobate crystals at low vertical temperature gradient The powder XRD measurements for lithium niobate phase and growth morphology using X-ray goniometer are also presented Chapter 3 describes the optical characterization methods for stoichiometry of undoped and doped crystal samples using absorption edge measurement and OH-1 IR spectra measurement... holographic recording in various doped SLN crystals and results compared with doped CLN crystal Further work was done on high-speed recording in doped SLN crystals Ultra high speed recording of analog images using shift multiplexing is also presented Chapter 6 describes the two-color holographic recording in doped SLN crystals Analysis of effect oxidation and reduction on two-color recording is done Further... sensitivity is still a big problem with lithium niobate crystals and need further study One way is to try various dopants and look for optimized behavior For WORM type storage devices, sensitivity (~500 cm/J) is 6 not really an issue but for read/write type of system it is very important to have media with high sensitivity 1.5 Stoichiometric lithium niobate Stoichiometric crystals have an advantage of having... holographic recording performance of doped lithium niobate crystals with stoichiometric composition Congruently grown lithium niobate crystals (Li ~ 48.6 mol%) have around 5 mol% (1 mol% of NbLi and 4 mol% of Li vacancy) of intrinsic defects that makes it unsuitable to efficient use for holographic recording Intrinsic defects density can be reduced by growing crystals with stoichiometric composition either... requirements for practical storage system is much higher than these values Sη=1cm/j and M/# = 10 This creates lots of scope for improvement in doped- SLN [47, 51, and 82] in terms of new dopants and annealing conditions [61] such that required performance can be achieved 1.6 Thesis overview This thesis presents the results of research done on growth, characterization and holographic recording performance of doped. .. Fig.6.7 Second recording of hologram in Fe:SLN using 5W/cm2 recording density and no gating light Fig.6.8 Experimental setup for Two – Color holographic recording using IR recording light and UV gating light Fig.6.9 Results of two color experiment performed with Fe:Mn:Tb:SLN-2 crystal sample with 6W/cm2 of recording light and 100 mW/cm2 of gating light Fig.6.10 Results of two color experiment performed with . TRANSITION METAL AND RARE EARTH DOPED STOICHIOMETRIC LITHIUM NIOBATE CRYSTALS FOR HOLOGRAPHIC RECORDING SANJEEV. NATIONAL UNIVERSITY OF SINGAPORE 2004 TRANSITION METAL AND RARE EARTH DOPED STOICHIOMETRIC LITHIUM NIOBATE CRYSTALS FOR HOLOGRAPHIC RECORDING SANJEEV SOLANKI. 2.2 Growth of undoped and doped SLN crystals 12 2.2.1 Stoichiometric undoped 12 2.2.2 Stoichiometric doped 19 2.2.3 Stoichiometric doubly doped 20 2.2.3 Stoichiometric triply doped 20 v 2.3