Identification of an upper limit to the laser pulse duration in photonic band-edge liquid crystal lasers

Abstract

Photonic band-edge liquid crystal (LC) lasers are an exciting field of research, offering potential in a range of applications from medical imaging to holographic projection. Much work has been done on improving the performance of LC lasers. However, due to historical limitations in pumping techniques, very little experimental work into the temporal dynamics of LC lasers has been published. In this paper, a laser diode pump source with a variable pulse duration is used to investigate the temporal characteristics of the resultant LC laser pulses, while maintaining a constant ratio of pump pulse energy to LC laser threshold. The existence of an upper limit to the output pulse duration of stimulated emission from an LC laser is presented, with a value of 3.5 (±0.1) ns for a DCM-doped cell and 5.2 (±0.2) ns for a Coumarin504-doped cell, irrespective of the laser diode pump pulse lengths, which exceed these values. Evidence is provided to show that the remainder of the optical energy within the pump pulse results in fluorescence emission. The results are in good agreement with the theory of organic dye dynamics and may provide possible future opportunities for electronic control of laser linewidth and coherence in addition to pump parameter optimization for improved LC laser performance.