Two-color facility based on a broadly tunable infrared free-electron laser and a subpicosecond-synchronized 10-fs-Ti:sapphire laser

Subpicosecond synchronization between a mirror-dispersion-controlled 10-fs Ti:sapphire laser and the Free-Electron Laser for Infrared Experiments has been achieved. The measured intensity cross correlation between the two lasers is consistent with a jitter of only 400 fs rms. The wide and continuous tunability of the free-electron laser (FEL; $4.2–300 \mathit{\mu }\mathrm{m}$) combined with ultrashort pulse duration of six optical cycles and high pulse energy of several tens of microjoules makes a series of two-color experiments possible in a previously inaccessible wavelength range. We demonstrate these capabilities by performing a two-color pump–probe experiment to study carrier cooling in GaAs. A FEL tuned from 8 to $17 \mathit{\mu }\mathrm{m}$ is used as the pump, and a synchronized Ti:sapphire laser pulse serves as the probe.