Tunable few-optical-cycle visible pulses with passive carrier-envelope phase stabilization from an optical parametric amplifier

One of the frontiers of ultrafast optics is the generation of few-optical-cycle light pulses with reproducible electric field profile, calling for stabilization of their carrier-envelope phase (CEP). Passive CEP stabilization is based on difference frequency generation (DFG) in a nonlinear crystal between two pulses sharing the same CEP; the DFG process cancels shot-to-shot CEP fluctuations (Baltuska et al., 2002). This effect is also present in an optical parametric amplifier (OPA), where the idler beam arises from a DFG process between pump and signal; in particular, in a noncollinear OPA (NOPA) pumped by the second harmonic (SH) of Ti:Sapphire, the idler is very broadband, but angularly dispersed due to the noncollinear geometry, making its exploitation very difficult. In this work we present a novel scheme for the generation of broadband tunable passively CEP-stabilized pulses in the visible spectral range. The system starts with an IR OPA in which both pump and seed are derived from the fundamental frequency (FF) of an amplified Ti:Sapphire laser. The passively CEP-stabilized narrowband idler is then spectrally broadened through white-light generation (WLG) and seeds a visible NOPA. The NOPA preserves the phase stability of the seed and provides pulses broadly tunable from 500 nm to 900nm.