Optical properties and lasing of organic dyes under single- and multi-photon excitation

Organic dyes fall under the category of easily accessible laser gain media in UV-visible, & near IR regions and are excellent systems, which help us understand various phenomena due to their high fluorescence quantum yields and broad gain bandwidths. Multi-photon absorption processes offer technologically relevant applications in medical science, optical switching, micro fabrication etc. The vital necessity of high flux densities under multi-photon excitations is also responsible for several other phenomena viz., self-phase modulation (SPM), stimulated Raman scattering (SRS), and white light continuum (WLC) generation. In the present work, we have recorded multi-photon fluorescence spectra of few organic dyes at 800 nm and 1064 nm excitation. The irradiance dependence of the fluorescence intensity reveals that two or more photons are required for absorption on pumping the dyes at 800 nm as well as at 1064 nm. The two-photon absorption (TPA) cross-sections of the dyes were also measured by transmission technique. Comparative studies were carried out by Z-scan technique. In addition, distributed feedback lasing (DFBL) in a dye due to higher order Bragg diffraction i.e., up to seventh order was recorded in few dyes. DFBL was also studied in a dye-pair by pumping with two pairs of beams to increase the tunability range. At last, triplet–triplet annihilation (TTA) studies on Zn-metalloporphyrin in a polymer matrix will be presented owing to the potential interest in recent years for employing it as a non-coherent photon up-conversion process for harvesting solar energy.