PbS nanoparticles saturable absorber for ultrafast pulse generation in 2-µm fiber laser

Abstract

Owing to its unique electronic and optical properties, lead sulfide (PbS) has stimulated great interest in various areas including ultrafast optics. Here, solution-processed PbS nanoparticles (NPs) deposited on a gold mirror are used as the saturable absorber (SA) to modulate a 2 µm Tm-doped fiber laser for ultrafast pulse generation. The PbS NPs have a broadband linear absorption decreasing from 350–2400 nm, with an absorption coefficient of > --> 20 % at 2 µm. Nonlinear optical absorption of the PbS NPs SA at 2 µm provides a modulation depth of 8.8% and a saturable intensity of 0.8 M W / c m 2 . A Tm-doped fiber laser mode-locked with the PbS NPs SA gives a maximum pulse energy of 7.3 nJ, pulse width of 4.24 ps, spectral width of 2.5 nm at ∼ 1993 n m . The damage threshold as high as 24 G W / c m 2 together with large modulation depth, low saturation intensity, and long-term stability make solution-based PbS NPs excellent candidates as light modulators in the 2 µm spectral region and beyond.