(Tm,Ho):YLF Laser Passively Mode-Locked with a Graphene Saturable Absorber

2-μm lasers are of particular interest for applications in medicine, remote sensing of CO2 and H2O in the atmosphere, optical communication systems, or time-resolved spectroscopy [1-3]. At this wavelength, most systems are nowadays based on Thulium, and Holmium-doped media. Ho-doped lasers are indeed attractive due to their emission above 2 μm, thus avoiding instabilities caused by water vapors absorption in air, and can be pumped at 1.9 μm with laser diodes, Co:Mg
₂
F or Tm
³⁺
-doped lasers. Another way of pumping Ho-doped materials consists in co-doping Tm-containing materials with Ho, which allows to use powerful commercially available laser diodes around 790 nm. Among other laser hosts used to generate 2μm emission, YLF has attractive properties, such as good thermal conductivity, low thermal-lensing effects and natural birefringence [4]. We then recently demonstrated for the first time a passively mode-locked laser featuring a (Tm,Ho)-co-doped YLF gain medium [5]. The laser was mode-locked with a reflective graphene saturable absorber (GSA) and generated picosecond pulses with 52 mW average power at 75 MHz repetition rate. However, the output pulse train exhibited a relatively high amplitude modulation of more than 10%. Here, we explore a novel laser configuration using a transmitting GSA and demonstrate better noise performances and output power.