In order to obtain high optical gain medium for low-threshold and compact polymeric lasers, a tert-butyl
substitutional rhodamine B (t-Bu-RhB) was synthesized and doped in PMMA film. The optical properties were
investigated and the results showed that the concentration of
t-Bu-RhB in PMMA could be increased to 6.9 wt % without
decrease of photoluminescence efficiency. Polystyrene (PS) PCs with bandgap of 595nm were fabricated by
vertical-deposition method. Resonator cavity was constructed by sandwiching t-Bu RhB doped films with two PS PCs.
When excited by a Nd:YAG laser beam(532nm,10Hz,8ns), single-mode laser emission was observed from the cavities
with dye concentration of 3, 5, 6.9, 10 wt %. Lasing emission is located at 592nm, with the full-width at half-maximum
(FWHM) of 1nm. Lasing threshold of the cavities dramatically decreased from 49.56 to 0.70 μJ/Pulse when the
concentration of t-Bu RhB increased from 3 to 6.9 wt%. Through enhancing the dye concentration to decrease lasing
threshold will save pump energy, which is not only important for economy of energy, but also in favor of extending the
life of such laser devices.