Coherent synthesis of visible-region optical pulses by using an optical parametric oscillator and a laser

We demonstrated coherent pulse synthesis between the carrier-envelope phase slip (CEPS) locked second-harmonic (SH) pulses from an optical parametric oscillator (OPO) and those from its pump laser. By using a single nonlinear crystal with cascaded gratings for parametric and SH generation, we maximized the common-mode rejection of environmental noise, obtaining a temporal overlap between the pulses as low as 30 attoseconds in an observation time of 20 ms. The CEPS frequencies of the pump laser and the OPO SH signal were locked individually to the same subharmonic of the repetition rate with a coherence time of at least 1.4 ms by using the pump supercontinuum as a common reference. Auto-correlation traces of the combined pulses showed an 8:1 ratio between the peak and the background once the CEPS frequencies were locked, in contrast with a much lower ratio when they were not locked, indicating successful pulse synthesis. This research illustrates the viability of using OPOs for sub-femtosecond optical pulse synthesis. The very low timing jitter and phase coherence between the pulses from this system, which spans from the ultraviolet (SH of the pump) to mid-infrared (idler), also make the system a powerful tool for optical spectroscopy and optical metrology. © 2009 SPIE.