No abstract

We describe herein a flexible and tunable random laser made from a flexible poly­(dimethylsiloxane) substrate. The substrate is prepared by casting via soft lithography from a lotus leaf to produce a micropapilla surface structure similar to that of a lotus leaf. The micropapilla provides efficient multiple scattering for the photons generated in the gain medium, and random lasing emerges because photons undergo closed-loop paths by scattering from three equilaterally arranged micropapillae. Given the diverse distribution of microscale features on the soft substrate, the random laser spectrum can be tuned by as much as 26.0 nm by changing the pump position. Furthermore, the random laser can be easily tuned by about 14 nm by flexing it, which modifies the micropapilla density and thereby changes the reabsorption strength of the laser dye. The photostability of the random laser is ensured by sealing the gain medium (i.e., dye solution) in a closed system. The results provide a promising method to realize a variety of laser-based applications such as optical biosensors on chips, microscale structural alteration detectors, flexible wearable devices, and multicolor (even white) random lasers.

In optically pumped laser systems, rare gas lasers (RGLs) are a field of great interest for researchers. Gas laser regimes with metastable Ne, Ar, and Kr atoms have been investigated, while studies of RGLs based on metastable Xe are sparse. In this work, when a strong excitation laser (2.92 mJ/pulse, 7.44 × 10 W/cm) was applied to excite Xe atoms from the ground state to the 6p[1/2] state, an interesting phenomenon emerged: An intense fluorescence of 980 nm (6p[1/2]-6s[3/2]) was produced. However, when the energy of excitation laser was decreased to 0.50 mJ/pulse (1.27 × 10 W/cm), the fluorescence of 980 nm became very weak. Besides, lifetime and decay rate constant of the 6p[1/2] state under the condition of E = 2.92 mJ are significantly different from either those measured by other groups or those of E = 0.50 mJ. These phenomena indicate that the high energy of excitation laser should trigger some new kinetic mechanisms. Further works identified that the new kinetic mechanism is the MIR ASE of 3408 nm (6p[1/2]-6s'[1/2]). The mechanisms are proposed as follows. Substantial 6p[1/2] atoms are produced by laser excitation. Then, the ASE of 3408 nm (6p[1/2]-6s'[1/2]) is quickly produced to populate substantial 6s'[1/2] atoms. The 6s'[1/2] atoms can readily arrive at the 6p[1/2] states through collision by virtue of the small energy difference (84 cm) and high collision rate constant of the transition from the 6s'[1/2] state to the 6p[1/2] state. As a result, the intense fluorescence of 980 nm is generated.