Abstract
We discuss the efficient generation of intense “water window” (0.28–0.54 keV) isolated attosecond pulses (IAPs) using a mid-infrared (MIR) waveform synthesizer. Our numerical simulations clearly indicate that not only a longer-wavelength driving laser but also a weak control pulse in the waveform synthesizer helps extend the continuum cutoff region and reduce the temporal chirp of IAPs in high-order harmonic generation (HHG). This insight indicates that a single-cycle laser field is not an optimum waveform for generating the shortest IAP from the veiwpoints of reducing the attochirp and increasing the efficiency of HHG. By combining a waveform synthesizer technology and a 100 mJ MIR femtosecond pulse based on a dual-chirped optical parametric amplification (DC-OPA) method, a gigawatt-scale IAP (55 as with 10 nJ order) in the water window region can be generated even without attochirp compensation. The MIR waveform synthesizer is highly beneficial for generating a shorter IAP duration in the soft X-ray region because there are no suitable transparent dispersive materials that can be used for compressing the attochirp.
Highlights
Isolated attosecond pulses (IAPs) via high-order harmonic generation (HHG) have opened up a new branch of ultrafast science called attosecond physics [1]
On the basis of our simulation parameters, we present a designed experimental setup with information on how to achieve a fully stabilized TW-scale 100 mJ MIR waveform synthesizer based on a dual-chirped optical parametric amplification (DC-optical parametric amplifier (OPA)) system
Because HHG is very sensitive to the electric field strength, only the central electric field peak contributes to the harmonic continuum in the cutoff region
Summary
Isolated attosecond pulses (IAPs) via high-order harmonic generation (HHG) have opened up a new branch of ultrafast science called attosecond physics [1]. In the past two decades, great advances have been made in attosecond physics, including the generation of IAPs with even shorter duration [2,3] and the real-time observation of electronic dynamics in atoms, molecules, and solids (see, for example, [4,5,6,7]). The efficient generation of IAPs driven by a Ti:sapphire laser has been limited to the XUV region. This is mainly due to the phase mismatch induced by free electrons from plasma because a high intensity greater than the ionization threshold of the medium is required for the generation of soft
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