Influence of trapping power and scanning speed on the quality of ordered structures formed in Z-scan-based optical trapping

Ordered structures formed in Z-scan-based optical trapping of colloidal liquids are evaluated by examining both the Z-scan trace and the diffraction pattern of the trapping region. It is found that there exits an optimum trapping power at which a highly ordered structure is achieved. This optimum trapping power exhibits a dependence on the scanning speed. In addition, a rapid deterioration in the quality of the ordered structures occurs with increasing scanning speed and it can be compensated by an increase of the trapping power. The two mechanisms that govern the annihilation dynamics of the ordered structures are clearly resolved at high scanning speeds due to their different response times to the change of the trapping light.