Nanosecond time-resolved spectroscopic and photographic measurements have been conducted for studying the mechanism of laser ablation of polymer films doped with biphenyl. Comparisons between the two different measurements made it possible to assign transient species observed during the ablation. The triplet state of the dopant was detected prior to the polymer ejection, while the excited singlet state was confirmed with its fluorescence. Besides these, biradicals such as C-2, CH, and CN were identified and plasma emission was observed, but only when the fluence was increased highly above the laser ablation threshold. The excited singlet and triplet states were concluded to be main transient species leading to ablation. Temporal behavior of the excited singlet state was simulated with a model involving the ground, excited singlet, and triplet states, and the ablation mechanism was discussed.