Precise control of timing and optical phase among multi-color femtosecond pulses (Invited Paper)

Abstract

Recent progress on ultrashort pulse lasers has made it possible to control the pulse timing and optical phases from different cavities very precisely. By applying detection and control techniques of the carrier-envelope phase to multicolor pulse sources with synchronized pulse timing, we obtained phase-coherent pulse-trains in different wavelengths. The pulse-trains have sufficient stability to achieve Fourier synthesis among optical fields. One of our test sources was a femtosecond optical parametric oscillator (OPO). Using a specially designed OPO whose signal and idler are sub-harmonics of the pump frequency, we obtained long-term stabilization of the optical phase among those three waves. Since the OPO also generates sum-frequencies of the three waves, six-color coherent pulse-trains from 425nm to 2550nm are available. Another test source was a passively synchronized mode-locked laser with two kinds of gain media, Ti:sapphire and Cr:forsterite. Although it is harder to reduce phase-noise between the different color pulses than in the OPO example, we can expect shorter pulse duration and higher average power from this type of coupled laser. These coherent multicolor pulse sources will be applied not only to shorter-pulse generation by field summation, but also to some applications that include competing non-linear processes among multicolor pulses.