Abstract

Previously, we achieved a stable high-flux isolated attosecond pulse (IAP) generation by high-order harmonic generation (HHG) in the soft x-ray region through a fully stabilized 50-mJ three-channel parallel waveform synthesizer [1] operating a 10 Hz. The generated sub-microjoule IAP pulse is then measured by frequency-resolved optical gating for complete reconstruction of attosecond bursts (FROG-CRAB) measurement with a result of 226-as duration [2]. It was a first-time characterization of the GW-scale IAP in experimental with a low repetition rate. However, depending on the original scheme of FROG-CRAB measurement, the use of the time of flight (TOF) device for data acquisition needs a long-time process. The total measurement time usually lasts tens of minutes for 20 fs scanning range with the delay step of 100 as. In this work, we applied an all-optical FROG-CRAB experiment [3] with expansion to characterize the IAP duration as a faster reconstruction method. As shown in Fig.1(a), the all-optical FROG-CRAB measurement scheme is using a weak gating pulse (<10^-3 in intensity ratio) as a perturb waveform applied to the HHG process with delay changes. The generated HHG spectra will show a modulation depending on the perturbing waveform. With the experimentally acquired FROG trace information, both the IAP and the gating waveform could be obtained through the reconstruction calculation. By excluding the use of the eTOF device, the harmonic spectra are acquired by the CCD camera, the total scanning time has been shortened to several minutes in this scheme. The measured FROG-CRAB trace is shown in Fig.1(b). According to the retrieved results (Fig.1(c) and (d)), the IAP is measured as 224-as duration, which could get a good agreement with the original FROG-CRAB measurement.

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