Samuel Bohman

Generation of 5.0 fs, 5.0 mJ pulses at 1 kHz using hollow-fiber pulse compression

We demonstrate methods to increase the energy incident on hollow fibers for spectral broadening by self-phase modulation. We used chirped pulses for spectral broadening, lowering the optical intensity to avoid ionization of the gaseous medium. We also used helium as a nonlinear medium and demonstrated the generation of 5.0fs, 5.0mJ pulses at a repetition rate of 1kHz using a pressure gradient hollow-fiber pulse compressor.

Generation of 5 fs, 0.5 TW pulses focusable to relativistic intensities at 1 kHz

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.

Pointing stabilization of a high-repetition-rate high-power femtosecond laser for intense few-cycle pulse generation

We have developed a beam stabilization system for high-power femtosecond lasers operating at a repetition rate of 1kHz. The beam pointing at a hollow fiber input was stabilized to within 1μm rms and the fluctuations of the broadened spectra and power were significantly improved. This technique enables us to increase the input power to a hollow fiber for intense few-cycle pulse generation.

Generating highly phase-matched isolated attosecond pulses with a carrier-envelope phase stabilized, TW-class, few-cycle laser

We generated highly phase-matched isolated attosecond pulses for the first time. This result can lead not only to the fundamental pump-and-probe-type experiments but to field-induced recolliding electron spectroscopy based on a single event.

Direct generation of highly phase-matched isolated attosecond pulses using multi-mJ, carrier-envelope phase stabilized, few-cycle laser pulses

One of the most crucial issues for the present attoscience is to increase the energy of isolated attosecond pulses (IAPs). Typical pulse energy of IAPs reported before is order of pJ, which is enough for streaking-type experiments[1], but not for fundamental pump-and-probe-type experiments using IAPs only. For this purpose, there are two crucial experimental challenges to demonstrate; one is to develop a multi-mJ few cycle laser with a stabilized carrier-envelope phase (CEP) and the other is the phase-matching between the few cycle pulses and high harmonics of them.

Generation of TW-class 2-cycle pulses using a pressure-gradient hollow fiber

We demonstrate generation of intense 5 fs pulses using a pressure gradient hollow fiber. The beam after pulse compression could be focused to a diffraction-limited spot with an intensity of 3times1018 W/cm2.

Spectral broadening of femtosecond laser pulses using a hollow fiber with symmetric pressure gradient

We propose and demonstrate a pulse compression technique using a symmetric pressure-gradient hollow fiber. This technique improves the spatial and spectral qualities of multi-mJ femtosecond laser pulses spectrally-broadened by self-phase modulation.

Pointing stabilization of high-power femtosecond laser for few-cycle pulse generation

We have developed a beam stabilization system for a high-power femtosecond laser operating at a repetition rate of 1 kHz. The beam position at a hollow fiber input was stabilized to within plusmn 1 mum rms and the output fluctuation was significantly improved.

Focusing of soft-x-ray high-order harmonics and ablation of metal surface

We have observed ablation patterns on metal surfaces made by focusing high-order harmonics in the soft-X-ray region. The ablation processes are investigated from the intensity dependence.