Energetic picosecond 10.2-µm pulses generated in a BGGSe crystal for nonlinear seeding of terawatt-class CO2 amplifiers.

We demonstrate what we believe to be a new approach to energetic picosecond 10.2-µm pulse generation based on nonlinear mixing of subnanosecond single-frequency 1338-nm pulses and broadband 1540-nm chirped pulses in a BGGSe crystal followed by a grating compressor for the purpose of seeding high-power CO2 amplifiers. The energy of the 10.2-µm pulses exceeding 60 µJ with 3.4%-rms fluctuation can be routinely obtained. Single-shot pulse duration measurement, performed by Kerr polarization rotation time-resolved by a streak camera, together with the pulse spectrum, indicates the pulse width is between 2.7-3 ps. Numerical calculations show that power broadening and dynamic gain saturation with Rabi-flopping can be induced with such an intense seed in a multi-atmospheric CO2 amplifier. These nonlinear effects greatly suppresses pulse splitting due to the comb-like spectrum of the CO2 molecule. A peak power exceeding 1 TW is expected after multipass of amplification while maintaining an appropriate high intensity by controlling the beam size along the path.

Robust sub-millihertz-level offset locking for transferring optical frequency accuracy and for atomic two-photon spectroscopy.

Robust sub-millihertz-level offset locking was achieved with a simple scheme, by which we were able to transfer the laser frequency stability and accuracy from either cesium-stabilized diode laser or comb laser to the other diode lasers who had serious frequency jitter previously. The offset lock developed in this paper played an important role in atomic two-photon spectroscopy with which record resolution and new determination on the hyperfine constants of cesium atom were achieved. A quantum-interference experiment was performed to show the improvement of light coherence as an extended design was implemented.