Low threshold blue conjugated polymer lasers with first- and second-order distributed feedback

We report on the fabrication of low threshold distributed feedback (DFB) polymer lasers based on a polyfluorene derivative containing statistical binaphthyl units (BN-PFO). First- and second-order feedback lasers have been realized. The emission was tuned in the wavelength range from $438\text{to}459\mathrm{nm}$ by varying the grating period and the film thickness. A threshold energy of $280\mathrm{pJ}$ /pulse was observed in second-order DFB structures, which could be further reduced to $160\mathrm{pJ}$ /pulse by employing first-order feedback in electron beam lithographically patterned structures with a period of $140\mathrm{nm}$ . In these first-order structures, laser oscillation at both edges of the photonic stop band was observed. These very low threshold values render BN-PFO a very promising material for future electrically pumped organic semiconductor laser diodes.