Generation of Sub-2 Cycle Optical Pulses with a Differentially Pumped Hollow Fiber

We report the generation of optical pulses with an energy of 0.55 mJ and duration of 1.6-cycle (4.4 fs) at repetition rate of 1 kHz using a differentially pumped hollow fiber and chirped mirrors. Compared to the statically gas-filled scheme, the differentially pumping hollow fiber is demonstrated to support more energy output with higher transmission efficiency, and to increase the spectral broadening due to a reduction of ionization defocusing in plasma at the fiber entrance. The differentially pumping technique is proved to be an effective way to obtain optical pulses with mono-cycle and higher energy.