High-efficiency polymethine dyes for passive Q-switch and mode locking of neodymium lasers

Abstract

New polymethine dyes (PD) based on benzene [c, d] indole were synthesized. Their spectral and nonlinear optical characteristics in liquid and polymer media have been studied. It was found that the relaxation times τ of the excited state of the new PDs are approximately the same as those of the dye 3274y, which is widely used as a passive Q-switch of neodymium lasers with a generation lengthwave of 1.06 μm. The low sensitivity of τ to changes in the chemical structure of such PDs indicates that the main contribution to the deactivation of the excited state is made by the benzene [c, d] indole heterocycle. High values ​​of the cross section in the range of 1.05-1.08 μm at low relaxation times allow the studied PD to be easily bleached in lasers at low intensities (about 10 MW/cm2). It is established that the photostability of the new PD significantly exceeds that for the dye 3274y. This is because they contain a saturated six-membered ring in the polymethine chain, which is much less reactive than the corresponding five-membered ring of dye 3274u with respect to the photoinitiator of free radicals of UV irradiation. It is shown that the efficiency of Q-switching and mode locking of new passive laser shutters is higher than their analogues based on the dye 3274y.