Study of relaxation times of polymethine dyes used for passive mode locking of solid-state lasers emitting between 750 and 850 nm

The relaxation times τ of the bleached states of polymethine dyes absorbing light in the 750 – 850-nm are determined by the direct pump – probe method. The effect of the dye structure and the solvent type on the relaxation time is discussed. The role of different intra- and intermolecular interactions in the relaxation of excited electronic states of the dyes is analysed. Polymethine dyes are found (with τ = 11 – 75 ps) that are promising for passive mode locking in Cr³⁺:LiCaAlF₆, Cr³⁺:KZnF₃, and Cr³⁺:LiSrAlF₆ crystal lasers.