The preparation and optical characterisation of novel organic crystals with applications in non linear devices

In recent years, novel non-linear organic materials have generated great interest in the development of all-optical non-linear devices. Such materials have been optically characterised, mainly for the purposes of second harmonic generation and electro-optic modulation, within the Chemistry department of Strathclyde University since the mid-1980's. This thesis documents the continued development and enhancement of this core research speciality in the growth, preparation and optical characterisation of two such novel organic non-linear materials, namely NMU and MBANP. A literature search that reviewed the linear and non-linear optical properties of a select number of novel organic non-linear materials was conducted. All too often sample crystal quality was not detailed and hence the quality of crystals upon which the material characterisation was based remained unknown. Surprisingly, the availability of reliable, accurate data was found to be scarce. The optical investigation of NMU represented the first ever examination of a high symmetry organic material to have been characterised at this facility. Unfortunately, the poor physical and handling properties of NMU were shown to be very similar to those of urea, from which NMU was originally derived. Non-linear coefficient evaluations were determined from second harmonic intensity experiments and calculations since the presence of phase-matching in the various crystal cut samples rendered the collection of Maker fringes unfeasible. Measured values were shown to be comparable to those of urea. Finally, NMU was shown not to be suitable for second-order electro-optic modulation purposes as the effect was symmetry forbidden and hence the signals recorded must have arisen from the converse piezoelectric effect. The further investigation of MBANP highlighted the possibility of angular insensitive Type I phase-matching, the first ever documented case for this material. Further improvement in the accuracy of refractive index determination, using a novel index measurement technique, provided the basis with which to define the optimum beam-crystal configuration for maximum second harmonic conversion efficiency at 1064 nm. (author)