WS₂/fluorine mica (FM) saturable absorbers for all-normal-dispersion mode-locked fiber laser

The report firstly propose a new WS₂ absorber based on fluorine mica (FM) substrate. The WS₂ material was fabricated by thermal decomposition method. The FM was stripped into one single layer as thin as 20 μm and deposited WS₂ on it, which can be attached to the fiber flank without causing the laser deviation. Similar to quartz, the transmission rate of FM is as high as 90% at near infrared wavelength from one to two micrometers. Furthermore, FM is a highly elastic material so that it is not easy to break off even its thickness was only 20 μm. On the contrary, quartz is hard to be processed and easy to break off when its thickness is less than 100 μm. Compared to organic matrix such as polyvinyl alcohol (PVA), FM has higher softening temperature, heat dissipation and laser damage threshold than those of organic composites. In our work, the modulation depth (MD) and non-saturable losses (NLs) of this kind of saturable absorber were measured to be 5.8% and 14.8%, respectively. The WS₂/FM absorber has a high damage threshold of 406 MW/cm², two times higher than that of WS₂/PVA. By incorporating the saturable absorber into Yb-doped fiber laser cavity, a mode-locked fiber laser was achieved with central wavelength of 1052.45 nm. The repetition rate was 23.26 MHz and the maximum average output power was 30 mW. The long term stability of working was proved to be good too. The results indicate that WS₂/FM film is a practical nonlinear optical material for photonic applications.