Studies pulsed Laser Deposited Ruby and Barium Titanate Thin Films for Tunable Optical Delay and Temperature Sensing Applications

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The present work aimed towards deposition of high quality ruby (Al2O3:Cr3+) and barium titanate (BTO) thin film via pulsed laser deposition (PLD) technique, for optical delay and temperature sensing applications. The ruby thin film was deposited as a function of substrate temperature, laser fluence, oxygen gas pressure and deposition time on quartz as well as sapphire substrate.The quality of film deposited via PLD depends on laser produced plasma (LPP). Therefore, LPP of ruby plasma has been studied by using planar copper Langmuir probe. The optimum deposition parameters obtained for the growth of highly C-axis oriented film of ruby were laser fluence ~ 23 J/cm2, gas pressure ~ 5 mbar and deposition temperature ~ 750ओ C. At optimum deposition parameters, epitaxial ruby thin film of thickness ~ 3500 nm was deposited on both side polished sapphire substrate for a deposition time of 6 hrs.The R-line width of this film was ~ 11.7 cm-1, comparable to single crystal of ruby, confirms highly crystalline nature of PLD ruby film. The nonlinear absorption coefficient and nonlinear refractive index of the film was measured using Zscan technique. The film was subjected to optical delay studies using 200 ns Gaussian pulse from Nd:YAG laser (532 nm) via degenerate two-wave mixing setup. Delay of 17 ns and pulse advancement of 12 ns corresponding to a group velocity of 205.9 m/s and - 291.7 m/s at +45ओ and -45ओ film orientation, respectively was observed. The temperature dependence of R1 and R2 line of epitaxial ruby thin film via PLD confirms its application as a photonic temperature sensor. Polycrystalline BTO thin film with tetragonal phase was deposited via PLD. The nonlinear coefficient of BTO film having thickness ~ 3300 nm was measured using Zscan technique. This film was subjected to optical delay studies using the same setup as that of used for ruby film. Subluminal as well as superluminal pulse propagation was observed on tuning the film orientation. The temperature dependent Raman spectrum of the BTO film was studied from 146 K - 506 K. This showed that BTO thin film can be explored as Raman temperature sensor. The optical delay was also studied in Ce:BaTiO3 crystal using millisecond pulses of CW He:Ne laser (632.8 nm). Effect of signal pulse width, pump intensity, pumpsignal polarization and crystal orientation on optical delay is systematically performed in the BTO crystal.
Supervisor: Alika Khare