Relative carrier-envelope-offset phase control between independent femtosecond light sources

The authors studied the measurement and control of relative carrier-envelope-offset phases among femtosecond light pulses whose optical frequencies have a subharmonic relation. They report the fluctuation dynamics of the phases and their control of two types of passive pulse-timing synchronized systems: passively synchronized mode-locked Ti:sapphire and Cr:forsterite lasers and a femtosecond subharmonic optical parametric oscillator. These techniques will facilitate Fourier synthesizing among subharmonic pulses in order to realize subfemtosecond pulse-train generation in the visible and infrared regions.