Dependence of amplified spontaneous emission threshold of BUBD-1 thin films on molecular orientation

The dependence of the amplified spontaneous emission (ASE) threshold on molecular orientation in vacuum deposited BUBD-1 films was investigated with the plane waveguide structure. The molecular orientations measured by the variable angle spectroscopic ellipsometry and the angular-dependent p-polarized PL spectra were optimized by varying the substrate temperature during deposition. Both of the optimized ASE threshold and the gain factor were obtained at the substrate temperature of 75 °C. The lowest ASE threshold of 3.3 μJ/pulse is only one third of that at 30 °C. The maximized net gain factor of 10.55 cm⁻¹ is 1.7 times higher than that of 6.11 cm⁻¹ at 30 °C. The enhancement of ASE performance of BUBD-1 film was ascribed to the lower horizontal ratio and surface roughness, which increased the total reflection and decreased the light scattering of light emission in the thin film light waveguide. It is an efficient way to optimize the molecular dipole orientation to enhance the ASE properties.