Sub-60 fs SESAM Mode-Locked Tm:LuYO3 Ceramic Laser

Summary form only given. Tm³⁺-doped cubic rare earth sesquioxide (Re₂O₃, Re = Lu, Y, or Sc) crystals have raised intense interest in the development of ~2 μm femtosecond lasers due to their excellent thermomechanical properties, comparatively low phonon energies and strong crystal fields [1]. In fact, femtosecond mode-locked (ML) lasers at ~2 μm based on Tm³⁺-doped sesquioxides have been demonstrated using saturable absorbers (SAs) such as SESAM [2], graphene [3] and single-walled carbon nanotubes (SWCNTs) [4] or pure Kerr lensing effect [5]. The main challenges for the crystal growth of large-volume Tm³⁺-doped simple or mixed sesquioxides are the very high melting points and the structural phase transitions occuring upon cooling in some of them. Alternatively, ceramics fabricated by the Hot Isostatic Pressing (HIP) sintering method is another option to obtain high quality Tm³⁺-doped sesquioxides including the mixed ones which exhibit spectral broadening due to compositional disorder. In 2018, pulses as short as 74/63 fs were achieved from a SESAM ML Tm:(Lu_2/3Sc_1/3)₂O₃ mixed ceramic laser before/after extracavity compression [6]. Here, we report on a SESAM ML Tm:LuYO₃ ceramic laser delivering pulses as short as 55 fs at 2048 nm with a pulse repetition rate of 78 MHz.