Large gain for crystalline thin films of thiophene/phenylene co-oligomer by photopumping with femtosecond laser pulses

We have evaluated the emission behaviors of crystalline thin films of thiophene/phenylene co-oligomers. Crystalline films of 2,5-bis(4-biphenylyl)thiophene (BP1T) were prepared on a substrate by vapor deposition followed by thermal treatment. The BP1T films contained crystalline domains several hundred micrometers in size. We examined the emission behavior of crystalline BP1T thin films by femtosecond laser excitation. Very high gains of over 500 cm−1 were obtained for the crystalline BP1T film. Furthermore, the emission cross section of the crystalline BP1T film was on the order of 10-16 cm2, rivaling that of dilute solutions of organic laser dyes.