Amplified spontaneous emission in para-sexiphenyl bulk single crystals

Amplified spontaneous emission (ASE) in single crystals of para-sexiphenyl grown in the β phase by vapor transport is demonstrated upon photoexcitation at 355nm. Excitation with femtosecond laser pulses leads to dual wavelength ASE at 427 and 450nm, while excitation with nanosecond laser pulses leads to ASE only at 450nm. The threshold fluences for nanosecond and femtosecond pumpings are determined to be 885 and 110μJ∕cm2, respectively. Additionally, the singlet exciton annihilation rate is measured to be γss=(1.2±0.1)×10−6cm3s−1.