Abstract
Since the first isolated attosecond pulse was demonstrated through high-order harmonics generation (HHG) in 2001, researchers’ interest in the ultrashort time region has expanded. However, one realizes a limitation for related research such as attosecond spectroscopy. The bottleneck is concluded to be the lack of a high-peak-power isolated attosecond pulse source. Therefore, currently, generating an intense attosecond pulse would be one of the highest priority goals. In this paper, we review our recent work of a TW-class parallel three-channel waveform synthesizer for generating a gigawatt-scale soft-X-ray isolated attosecond pulse (IAP) using HHG. By employing several stabilization methods, we have achieved a stable 50 mJ three-channel optical-waveform synthesizer with a peak power at the multi-TW level. This optical-waveform synthesizer is capable of creating a stable intense optical field for generating an intense continuum harmonic beam thanks to the successful stabilization of all the parameters. Furthermore, the precision control of shot-to-shot reproducible synthesized waveforms is achieved. Through the HHG process employing a loose-focusing geometry, an intense shot-to-shot stable supercontinuum (50–70 eV) is generated in an argon gas cell. This continuum spectrum supports an IAP with a transform-limited duration of 170 as and a submicrojoule pulse energy, which allows the generation of a GW-scale IAP. Another supercontinuum in the soft-X-ray region with higher photon energy of approximately 100–130 eV is also generated in neon gas from the synthesizer. The transform-limited pulse duration is 106 as. Thus, the enhancement of HHG output through optimized waveform synthesis is experimentally proved.
Highlights
IntroductionSince the first isolated attosecond pulse (IAP) was demonstrated by high-order harmonics generation (HHG) in 2001 [1], attosecond science has emerged as a vital frontier research area of ultrafast science [2,3,4]
We review our recent work of a TW-class parallel three-channel waveform synthesizer for generating a gigawatt-scale soft-X-ray isolated attosecond pulse (IAP) using high-order harmonics generation (HHG)
Through the HHG process employing a loose-focusing geometry, an intense shot-to-shot stable supercontinuum (50–70 eV) is generated in an argon gas cell. This continuum spectrum supports an IAP with a transform-limited duration of 170 as and a submicrojoule pulse energy, which allows the generation of a GW-scale IAP
Summary
Since the first isolated attosecond pulse (IAP) was demonstrated by high-order harmonics generation (HHG) in 2001 [1], attosecond science has emerged as a vital frontier research area of ultrafast science [2,3,4]. Most attosecond pump-probe experiments (including streaking measurements) have to employ a two-color scheme to compensate for the energy lack: an IAP plus a near-infrared (NIR) femtosecond pulse [15, 16], where the NIR pulse serves as the pump or probe pulse. With this scheme, the large ponderomotive energy associated with NIR pulses often causes difficulty in the interpretation of experimental observations.
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