Two-photon pumped forward, backward and random lasing in a stilbazolium dye nanocomposite solution containing LAPONITE® as a scattering center

Multiphoton upconversion lasing in scattering gain media has attracted considerable attention in recent years. LAPONITE (R) is a scattering medium consisting of 2-D nano-discs that can be dispersed as a transparent solution in aqueous media and forms a gel at high concentration. In this paper, we demonstrate two-photon pumped upconversion regular lasing along forward and backward directions as well as random lasing along all other directions. The gain medium was a mixture of PRL-L5 dye solution in DMF with a water solution of LAPONITE (R) in which LAPONITE (R) nano-discs of 25-30 nm diameter may form large-size particles of several hundred nanometers due to electrostatic binding between the dye molecules and the LAPONITE (R) nano-discs, and therefore can produce more efficient scattering feedback for random lasing generation. Using 795 nm and 100 fs laser pulses as two-photon pump sources, we observed random lasing at around 500 nm, characterized by both spectral and temporal narrowing in all directions apart from the traditional (colinear forward/backward) lasing directions. The peak spectral intensity of random lasing is similar to 3.4 times higher than the normal fluorescence emission, but 105-106 times lower than the traditional forward lasing. This study shows the feasibility of generating both traditional forward/backward and random lasing in a moderately scattering gain medium for applications in diverse fields such as remote sensing, optical communications, and upconversion imaging.