Passively Mode-locked Diode-pumped Yb:CaF2 Oscillator

Ultrafast (UF) mode-locked (ML) lasers are extremely powerful tools in scientific research and industrial applications including material processing, nonlinear optics, attosecond science, metrology, etc. The most popular UF Ti:sapphire laser applications are limited by its high ownership cost, system complexity and low power transfer efficiency. Yb3+:CaF2 has been recognized as a promising candidate for a high efficient and high power femtosecond laser, for its simple energy-level scheme, high quantum efficiency (~1), very small quantum defect (<10%), long upper-state lifetime (2.4 ms), broad emission spectrum (>70 nm), high thermal conductivity and compatibility with high power InGaAs diode pumping. Two types of Yb3+:CaF2 ML resonators based on semiconductor saturable absorber mirrors (SESAM's) and Kerr lens mode-locking (KLM) have been demonstrated and analyzed in detail. A Kerr-lens ML oscillator was constructed for continuous-wave modelocking operations by incorporating an additional optical element with an enhanced nonlinear Kerr coefficient, which represents the first such investigation for an Yb3+:CaF2 oscillator to our best knowledge.