Sub-5 fs pulse generation from a noncollinear optical parametric amplifier

Abstract

Transform-limited visible pulses with as short as sub-4 fs duration have beengenerated for the first time by several improvements made to our previousnoncollinear optical parametric amplifier (NOPA). All of the signal–idlergroup-velocity matching and pump–signal pulse-front matching and angulardispersion matching of the parametric amplification processes and the finalfine tuning of dispersion compensation using deformable mirror after apair of chirped mirrors are essentially important to generate such shortpulses. We demonstrated the generation of a continuous, simultaneouslyphase-matched 250 THz parametrically amplified spectrum. Resultingvisible–near-IR signal-wave pulses have been compressed to a 4 fs duration using amicro-machined flexible mirror. Feedback for the iterative computer-controlleddispersion compensation algorithm is based on pulse characterization by asecond-harmonic generation frequency-resolved optical gating. Tunableoperation with bandwidth-limited sub-10 fs pulses in the visible (550–700 nm)and near infrared (900–1300 nm) was also performed by changing theseed delay with respect to the pump after increasing the seed chirp. TheNOPA is one of the most useful light sources for ultrafast spectroscopy atthe present stage on an extremely short timescale. Application to thevibrational wavepacket dynamics in terms of dynamic mode couplingis discussed. The future prospect of the NOPA is described at the end.