250-MHz synchronously pumped optical parametric oscillator at 2.25-2.6   {\mu}m and 4.1-4.9 {\mu}m
  A compact and versatile femtosecond mid-IR source is presented, based on an optical parametric oscillator (OPO) synchronously pumped by a commercial 250-MHz Er:fiber laser. The mid-IR spectrum can be tuned in the range 2.25-2.6 \mu m (signal) and 4.1-4.9 \mu m (idler), with average power from 20 to 60 mW. At 2.5 \mu m a minimum pulse duration of 110 fs and a power of 40 mW have been obtained. Active stabilization of the OPO cavity length has been achieved in the whole tuning range. 
Nicola Coluccelli, Helge Fonnum, Magnus Haakestad, Alessio Gambetta,   Davide Gatti, Marco Marangoni, Paolo Laporta, and Gia...
physics.optics