Dipolar organic materials producing highly efficient laser-like emission

摘要

High-efficiency laser-like emission at low thresholds in dipolar organic materials upon pulsed optical excitation, without using any external mirrors. Unusually high conversion efficiencies and low thresholds in laser-like emission have been observed in the solutions of organic molecular salts having large dipole moments and specific dye molecules having high photoluminescence efficiencies. Pumped with frequency-doubled pulses from a Nd:YAG laser, conversion efficiencies in the range of 15-40% were achieved without incorporation of external mirrors. The threshold pump energies for such emission have been observed to be low (8 μJ). The spectrally narrowed output beam was found to have low divergence, high degree of polarization, and pulse-width less than that of the excitation pulses (50 picoseconds). The exceptionally low threshold (1 μJ) and high energy conversion efficiencies observed in molecular salts have been attributed to the large excited-state dipole moment of these noncentrosymmetric molecules favoring strong cooperative (laser-like) emission in spite of small photoluminescence quantum efficiencies.