Study On Growth And Optoelectronic Properties Of DAST Crystals

Organic nonlinear material 4-N,N-dimethylamino-4?-N?-methyl-stilbazolium tosylate(DAST)crystal have attracted great attention because of its potential for high frequency electro-optic modulation,frequency conversion?THz wave generation and detection.Unfortunately,further applications of DAST are limited by long time consuming for the growth of DAST crystals and the resulting small crystals.Up to now,most of the related previous studies focused on the growth and physical properties of the DAST crystals.Based on this,the large DAST single crystals were successfully grown in this dissertation.Particularly,the optical rectification effects of the as-grown DAST single crystals were investigated.Moreover,we developed a new pathway to induce the growth of DAST micro crystals by external electric field.The main research results of this work include:(1)Firstly,DAST was synthesized and purified by ourselves,by which methanol solution of DAST was prepared.Accordingly,we explored the growth of DAST crystal with large size and excellent optical quality by the slope nucleation method(SNM),and the DAST crystal with the size of 9×9×6 mm~3 was successfully grown.We also found that if the DAST concentration in the solution was increased,the growth rate of DAST crystal along the c axis increased.We tested and characterized the DAST crystal,verifying that DAST single crystals with excellent optical quality have been obtained.(2)Based on the polar characteristic of DAST molecule,we proposed a new method for inducing the growth and alignment of DAST micro nancrystals by an applied electric field.The results showed that the applied electric field indeed can change DAST crystal growth orientation.It provides a feasible method for the controlled growth and device applications of DAST crystals.(3)Based on the growth of DAST single crystal,the optical rectification effect of DAST crystals were investigated,and thus the equation of polarization field in Z axis direction when the light field is incident along[001]direction was deduced.We set up the optical rectification test platform,and the DAST optiacl rectification effect is measured by the self-built platform.The results showed that both the optical rectification voltage and polarization rotation angle curve experimentally measured are in accordance with the theoretically deduced formula,both demonstrating that these signals are resulted from the optical rectification of DAST crystals.Particularly,we also proposed a new method for adjusting the optical rectification of DAST crystal by external stress.It is found that the intensity of the optical rectification signal is enhanced with the increase of the stress.The experimental results in this thesis are helpful for prompting the applications of DAST crystals in photoelectric detectors.