We report on excitation of photoluminescence via two-photon absorption (2PA) in dye-doped liquid crystal droplets using tightly focused cw-laser illumination at 1064nm wavelength. The photoluminescence of the 2PA dye C40H54N2O2 (MBAPB) dispersed inside the 7CB liquid crystal host increases as square of the laser tweezers' irradiance. The 2PA cross-section of MBAPB was measured by femtosecond Z-scan method. The polarization and temperature dependence of the photoluminescence corroborated the presence on the dye's molecular alignment inside the nonpolar liquid crystal host. The molecular alignment via the host-dye interaction can be used for the laser manipulation of micro-objects (e.g., doped liquid crystal droplets) in micro-fluidic/mechanical applications.
Molecular Crystals and Liquid Crystals,
Vol. 489 (2008), pp. 310-319