| dc.description.abstract | Good opticalquality LAP and dLAP crystals were grown from aqueous solutions by solvent evaporation and slow cooling. Problems associated with crystal growth, such as microbial growth in the solution, were systematically studied and remedied. Experimental and simulation studies on the Xray powder diffraction patterns were used to verify the accuracy of existing structure reports. A dislocation etchant was formulated, tested, and successfully applied to identify the nature of mechanical and laserinduced damages. Knoop hardness anisotropy was evaluated in the cleavage planes of LAP and dLAP. Detailed statistical studies were carried out on laserinduced damage in LAP and dLAP using both nanosecond and picosecond Nd:YAG laser pulses. The nature of laserinduced damage was then examined using optical and electron microscopy, dislocation etching, and hardness anisotropy. It was found that laser and mechanical damages do not involve plastic deformation of the lattice around the damage centres.
Good opticalquality single crystals of typeII semiorganic NLO crystals, ZTS and BTCC, were grown from aqueous solutions. ZTS crystals were generally easier to grow than BTCC, which often formed with incomplete morphologies and inclusions. However, good BTCC crystals large enough for characterization were obtained from solutions under low evaporation rates. The grown crystals were characterized for various physical properties. BTCC was found to have lower absorption around 1064 nm than ZTS, which may be attributed to the presence of fewer N-H bonds causing absorption at that wavelength. Thermal analyses showed that both ZTS and BTCC have melting points above 200°C and decompose upon melting. Vibrational spectroscopic studies provided insights into the structure and bonding in these relatively unknown materials. A detailed analysis of the effect of metal complexation on thiourea vibrations indicated that metals bond to thiourea via the sulfur atom rather than through the NH group. Phasematching angles for SHG in these crystals were measured under different polarization interaction conditions. Hardness studies revealed a high degree of anisotropy in both ZTS and BTCC. Laserinduced damage studies indicated that their damage resistance is comparable to that of LAP. The damage patterns reflected the symmetry of the crystal plane, and the relation between mechanical hardness anisotropy and laserdamage morphology indicated a direct correlation between the two.
Single crystals of MHBA were grown from various solvents. A systematic study was undertaken to analyse the growth behaviour of MHBA in different solvents and their mixtures. Attempts were also made to modify the growth habit by metal poisoning of the solution. Spectrophotometric studies revealed that crystals grown from chloroform-acetone mixtures exhibited lower absorption and a wider transparency window than those grown from acetic acid-water solutions, making them better suited for optical applications. Thermal analysis showed that MHBA does not undergo any hightemperature phase transition and does not sublime appreciably up to its melting point. However, slight colouration was observed in the melt when it was held for a prolonged duration. Secondharmonic rings generated through nearly collinear phase matching were used to obtain phasematching angles. Mechanical hardness assessment showed that MHBA is softer than the semiorganic crystals studied. Laserdamagethreshold experiments revealed high resistance to laser damage, and the damage morphologies showed a strong correlation with mechanical hardness anisotropy. | |
