Abstract
We have demonstrated the generation of 5 fs, 0.5 TW pulses at 1 kHz repetition rate using a pulse compression technique in a hollow fiber with a pressure gradient. Owing to the excellent beam quality by passing through the hollow fiber, the beam after pulse compression could be focused to a nearly diffraction-limited spot size. We obtained for the first time a peak intensity as high as 5x10(18) W/cm(2) in the 2-cycle regime.
Highlights
Ultrashort laser pulses offer a unique opportunity to investigate ultrafast laser-matter interactions
The problem is the occurrence of self-focusing and ionization of the gas medium near or around the entrance of the fiber, which degrades the coupling between the beam and the hollow fiber and subsequent spectral broadening due to Kerr-based self-phase modulation (SPM) inside the fiber
In our recent theoretical study [14], we found that there is a tradeoff between energy throughput and spectral broadening when the medium is strongly ionized by multiphoton ionization (MPI), which starts to occur at an intensity of approximately 2x1014 W/cm2 for neon
Summary
Ultrashort laser pulses offer a unique opportunity to investigate ultrafast laser-matter interactions. After the beam is coupled to the fundamental mode of the fiber under the ideal condition, for spectral broadening to occur, the beam undergoes an SPM-based nonlinear process. Such a situation can be realized by a pressure gradient method, in which the gas pressure is distributed from zero at the entrance to the maximum at the exit of the fiber. With this technique, we have already generated 9.8 fs, 5 mJ pulses compressed from 40 fs, 8.5 mJ input pulses at a repetition rate of 10 Hz [10] and 10 fs, 2.5 mJ pulses from 23 fs, 5 mJ input pulses at a repetition rate of 1 kHz [12]. For efficient temporal compression of an intense laser pulse to the few-cycle regime, the peak intensity of the pulse inside a fiber must be below or comparable to the threshold value of MPI, in addition to the careful adjustment of coupling between the input beam and the fiber
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