ИСТИНА

Development of compact two photon pumped lasers (TPPL) converting infra-red radiation into visible is a challenging task nowadays. Organic dyes are often used for creation microlasers since they can be easily assembled into resonators of various shapes. One of the most promising materials for TPPL is DCM (4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran) dye due to its high value of two-photon absorption cross-section. Here we report on the observation of room-temperature two-photon lasing in DCM spherical microresonators made by self-assembly method. Microspheres with the diameter of 5-10 um were studied using a nonlinear-optical microscopy setup based on the titanium-sapphire femtosecond laser operating at the wavelength of 800 nm. The fundamental beam was focused into a spot of 1 um in diameter. We demonstrate that whispering gallery modes (WGM) are excited in the DCM microspheres in the spectral range of the two-photon fluorescence (TPF). Polarization-resolved nonlinear-optical microscopy shows that both TE- and TM-polarized WGMs appear, with the quality factor up to 300 and the free spectral range of 10-20 nm. Lasing effect was observed for individual WGMs as a pronounced deviation of the TPF intensity dependence from quadratic power law and being undisturbed in non-resonant case. Numerical modeling supports the experimental data.