Wideband tunable passively Q-switched fiber laser at 28 μm using a broadband carbon nanotube saturable absorber

Abstract

We propose and demonstrate a widely tunable passively Q-switched Ho3+/Pr3+-codoped ZrF4-BaF2-LaF3-AlF3-NaF fiber laser operating in the 2.8 μm mid-infrared (MIR) waveband based on a single-walled carbon nanotube (SWCNT) saturable absorber (SA). The SWCNTs have diameters ranging from 1.4 to 1.7 nm. The modulation depth and saturation intensity of the SWCNT SA measured at 2850 nm are 16.5% and 1.66  MW/cm2, respectively. Stable Q-switched pulses with the shortest pulse duration of 1.46 μs and the maximum pulse energy of 0.43 μJ are achieved at a launched pump power of 445.6 mW. The combined use of a broadband SWCNT SA and a plane ruled grating ensures a broad continuously tuning range of 55.0 nm from 2837.6 to 2892.6 nm. The output powers, emission spectra, repetition rates, and pulse durations at different tuning wavelengths are also characterized and analyzed. Our results indicate that SWCNTs can be excellent broadband SAs in the 3 μm MIR region. To the author’s knowledge, this is the first demonstration of a widely tunable carbon-nanotube-enabled passively Q-switched fiber laser operating in the 2.8 μm MIR waveband.