Toward the Generation of Isolated Attosecond Pulses in the Water Window

Abstract

The coherent attosecond pulse in the water-window spectral region could be a powerful tool for studying the ultrafast electronic dynamics of biological samples in water. We propose a scheme to generate isolated attosecond pulses in water-window region, by exploring the high-order harmonic generation in helium atoms driven by a multicycle two-color optical field synthesized with an intense 2,000 nm, 20 fs pulse and its detuned frequency doubled pulse. The calculations show that isolated 67 as pulses in the water-window can be produced in this way. We also describe how to generate such a driving laser pulse with stabilized carrier-envelop phase from a two-stage optical parametric amplifier. With a pump source at 800 nm, the output pulse is tunable from 1.2 to 2. 4 μm, and the output average power is 1.2 W for 1. 5 – 1. 7 μm region. Due to the differential frequency process, the output infrared pulse is self-phase-stabilized.