Laser Q-switching

Adv.Mater.http://dx.doi.org/10.1002/adma.201306322(2014)

Monolayers of molybdenum disulphide (MoS₂), a transition-metal dichalcogenide, are interesting for electronic and optoelectronic applications, because they possess a direct bandgap in the visible range. Now, by introducing suitable defects through varying the ratio of Mo ions to S ions, Shuxian Wang and co-workers from Shandong University in China have demonstrated that a stack of MoS₂ sheets can act as a saturable absorber. The introduction of defects reduces the bandgap of MoS₂ atomic layers, causing the material to exhibit broadband saturable absorption that can be used to passively Q-switch a laser. Using over 30 stacked monolayers of MoS₂ prepared by pulsed laser deposition, the team succeeded in making passively Q-switched lasers that operate at wavelengths of 1.06 μm, 1.42 μm and 2.1 μm and have Nd:GdVO₄, Nd:Y₅Ga₅O₁₂ and Tm:Ho:Y₅Ga₅O₁₂ crystals as gain materials. Pulses were generated with sub-microsecond temporal widths and microjoule energies at repetition rates of hundreds of kilohertz, giving maximum output powers of up to a few hundred milliwatts. The team envisages that the findings will aid the design of variable bandgaps in two-dimensional optoelectronic crystals.