Spectrally narrowed emissions in 2,5-bis(4-biphenylyl)thiophene crystals pumped by fs laser pulse

Spectrally narrowed emission (SNE) in 2,5-bis(4-biphenylyl)thiophene (BP1T) crystals is investigated using fs laser pulse. Two different types of narrowing are observed at different vibronic emission bands with increasing pump intensities. Based on their pump intensity dependence and illumination area dependence, we assign the SNE at 20,200 cm−1 (β-band) to amplified spontaneous emission (ASE) and the SNE at 21,600 cm−1 (α-band) to superfluorescence rather than ASE.