Multiphoton Resonance in Attosecond Transient Absorption

Round 1

Reviewer 1 Report

The manuscript presents a thorough and detailed theoretical study of resonant XUV transient absorption in presence of an IR or VUV exciting field. For its clearness and completeness this work is worth publishing with only minor corrections (see below).

One remark that the authors are invited to consider concerns the limited discussion of the possible implications of this work for experimenters interested in this field. This is not a strict requirement, but it may be useful to provide more precise indications that would allow other researchers to put the predictions of this work into practice.

Minor points:

• "1snp" is not a very clear notation. Moreover, there is a mix-up of italics/non-italics throughout the paper. It may be better to use always italics for "s" and "p".
• Rephrase "allows the integration of Eq. (2) analytically integrated"
• Although present in the reference, it may be useful to give a definition of KBBF in the text or in the Abbreviations.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

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Comments for author File: Comments.pdf

Author Response

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Reviewer 3 Report

In the present paper, Xue et al. developed a theory to describe the interactions of atomic states with VUV and XUV light based on high-order time-dependent perturbation theory. The fine structure near the resonance is well explained within the developed theory. This study is publishable after a major revision.

Major Revision:

• In the introduction, the authors have mentioned both the use of IR and XUV as pump and probe. However, based on the experimental schemes whether it’s (IR/XUV) a pump or probe, different dynamical processes can be probed. It is desirable that the authors clearly distinguished between these. There could be four different kinds of set up based on whether IR/XUV is a pump or probe.

• Page 2, line 38-41, it’s not very clear what the authors are trying to explain. Why VUV filed only weekly affect the dynamical process? What particular transition the authors are talking about? This should be clarified. In fact, the authors have not described what is the difference between the expected dynamics in VUV and XUV?

• To my understanding the main motivation for the developed theory is to describe the combined VUV and XUV effects. A discussion on how this combination is useful would be important for the readers. While the developed theory extends the scope of attosecond physics, what experimental scopes are the authors trying to improve?

• Could the authors explain the reason or cite appropriate literatures of choosing the simulation parameters provided in Page 2, line 66-69?

• The periodic modulation observed both in positive and negative time delays in Figure 1b and 2. Is it possible to change the time delay between the VUV and XUV pulse to control the interference pattern or their decay?

• In a pump-probe transient absorption experiments, the transient signal and the modulated signal is typically absent in case of negative time delays. Could the author envision such pump-probe approach with the developed theory?

• Many important papers on the ATAS of He have not been cited e.g. : 1) Petersson et al. PRB, 96, 2017. 2) Birk et al. J. Phys. B: At. Mol. Opt. Phys. 53, 2020

• The chirp and phase can be used to explain the slope in the absorption fringes. Can the authors use these fringes to extract attosecond dynamical information? If so, this should be included in the revised manuscript.

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

The authors have addressed most of the concerns. The manuscript is publishable. I still have a question:

1) In pump-probe transient absorption experiments, the transient signal is absent in case of negative time delays. Therefore, I am still not sure why did they observe signal and modulation in negative time delays? What signal is plotted in Figure 2? Is it a change in absorption between the pump on and the pump off signal?

Author Response

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Author Response File: Author Response.pdf