Two- and Three-Photon Pumped Regular and Random Lasing Behaviors in a Scattering Dye Solution With Suspended Polystyrene Microspheres

Regular and random lasing properties in a multiphoton active and highly scattering dye solution containing polystyrene microspheres of 366-nm diameter have been experimentally studied. Using 100-fs laser pulses of wavelength 790 nm and 1300 nm as the two- and three-photon excitation sources, the frequency-upconversion regular lasing of ~610 nm wavelength can be generated along both the forward and backward directions, characterized by high directionality, higher spectral intensity, and remarkable spectral narrowing. In the meantime, the random lasing can also be observed along all other directions, characterized by only spectral narrowing but with much lower spectral brightness. The spectral brightness ratio between the forward regular lasing and the random lasing is ( $10^{4}$ - $10^{5}$ ):1. Comparing to the input pump beam of ~3 mm diameter and divergence angle of $\theta _{0}~\approx ~0.9$ mrad, the forward lasing beam size and divergence angle were ~7 mm and ~(3-4) $\theta _{0}$ , whereas the corresponding parameters were ~5 mm and $\sim 1.5~\theta _{0}$ for the backward lasing beam, indicating the phase-conjugation property of the latter.