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 355 nm . Excitation with femtosecond laser pulses leads to dual wavelength ASE at 427 and 450 nm , while excitation with nanosecond laser pulses leads to ASE only at 450 nm . The threshold fluences for nanosecond and femtosecond pumpings are determined to be 885 and 110 μ J ∕ cm 2 , respectively. Additionally, the singlet exciton annihilation rate is measured to be γ ss = ( 1.2 ± 0.1 ) × 10 − 6 cm 3 s − 1 .