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REVIEW 4 major objections 5 minor 11 references

Comment on "Comment on Attosecond electron microscopy and diffraction"

T0 review · 4 major / 5 minor · reviewed 2026-08-08 · deepseek-v4-flash

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Pith's one-line read This reply defends a previous attosecond electron microscopy result against a critique that its graphene diffraction signals were optical artifacts, presenting control measurements that isolate genuine ultrafast intraband dynamics.

desk verdict This reply adds two useful control measurements that blunt the optical-interference charge, but the 625-as gating claim rests on an unverified cancellation assumption that every downstream number inherits. read the letter →

arxiv 2502.06592 v1 pith:62CELWGU submitted 2025-02-10 physics.optics

Dandan Hui , Husain Alqattan , Mohamed Sennary , Nikolay V. Golubev , Mohammed Th. Hassan This is my paper · ORCID
classification physics.optics
keywords attosecondelectronmicroscopyopticalgatingultrafastdiffractiongrapheneintrabanddynamicsbackgroundsubtractionpulsetrainstime-resolvedimagingpolarization
verification ladder T0 review T1 audit T2 compute T3 formal

The pith

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The reading

This reply defends a previous attosecond electron microscopy result against a critique that its graphene diffraction signals were optical artifacts. The authors argue that their attosecond optical gating gives true temporal resolution, unlike electron pulse-train methods where the envelope sets the resolution, and they present new control measurements showing that background laser interference near the beam blocker does not track the diffraction peaks. They further report that lowering the pump field removes the diffraction dynamics while leaving the background oscillations unchanged, which they take as evidence that the signals reflect field-induced intraband motion in graphene. If the reply is right, the original experiment stands as the first realistic attosecond imaging of electron dynamics in a material.

What carries the argument

The central mechanism is attosecond optical gating: a 625-attosecond window carved out of a ~300-femtosecond photoemitted electron pulse, producing about 5,000 gated electrons per image. The reply argues that the leading and trailing circularly polarized parts of the optical gating pulse generate evanescent fields that are separated in time by π and opposite in handedness, so they cancel on the mesh and leave only the plasmon field of the linear portion; this step is what distinguishes their method from polarization gating in high-harmonic generation. Also load-bearing is the background-subtraction logic: ungated electrons are assumed to be insensitive to the pump-induced dynamics and are removed as noise, with the gated signal normalized to reference diffraction counts.

What would settle it

A direct test would be to vary the optical gating pulse duration while holding the pump fixed; a genuine gated signal should scale with the gated-electron fraction, while an interference artifact would not. A second decisive check is to replace the graphene sample with a featureless film under identical conditions and look for the same diffraction oscillations.

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Extended reading notes

Core claim

The paper claims that the time-resolved diffraction oscillations observed in their graphene experiment are genuine signatures of ultrafast intraband electron dynamics, not interference from scattered light or electron-beam modulation. The load-bearing distinction is that their optical gating isolates a 625-attosecond window of the electron pulse, so only 0.2% of the beam carries the dynamics, while the ungated electrons are blind to the pump and are subtracted as background; pulse-train methods, by contrast, measure an envelope-limited average. The reply also asserts that the leading and trailing circularly polarized parts of the gating pulse cancel on the mesh, leaving only the linear-polarization plasmon field, and that the observed background modulations near the beam blocker have amplitudes too small to create the peak signals, as shown by new shadow-region and low-power control measurements. On the terminology question, the authors hold that diffraction imaging qualifies as microscopy, pointing to scanning tunneling microscopy as a precedent.

Load-bearing premise

The reply depends on the assumptions that ungated electrons are truly blind to the pump-induced dynamics and can be cleanly subtracted, and that the leading and trailing circularly polarized parts of the gating pulse cancel on the mesh; neither is demonstrated by a direct measurement in this reply.

Editorial extensions

If this is right

  • If the reply is correct, the original diffraction data remain valid evidence of attosecond-scale intraband dynamics in graphene.
  • The optical gating method would be established as providing true temporal resolution independent of the pulse-train envelope, which would set it apart from recent pulse-train approaches.
  • The distinction between gating-based and pulse-train-based attosecond electron microscopy would become a central methodological point for future work.
  • The raw-data sharing and control measurements would provide a template for defending time-resolved electron microscopy against artifact claims.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • A stronger defense would have included a direct measurement of the gated-electron fraction or a single-shot trace, but the reply's case rests entirely on control comparisons rather than independent replication.
  • The cancellation of the circularly polarized parts of the gating pulse is asserted rather than derived or measured, leaving a specific assumption open to experimental check.
  • If the gating-based distinction is correct, it implies that some published attosecond pulse-train results may need to be reinterpreted as envelope-limited, a claim the reply makes but does not fully establish.
  • The terminology argument that diffraction qualifies as microscopy would apply equally to the pulse-train works the reply criticizes, so the naming debate is not settled on the merits.
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Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, and a circularity audit.

Referee Report

4 major / 5 minor

Summary. This manuscript is a reply to the commentary by Baum and Ropers on Hui et al. (Science Advances 2024), defending the claim that the observed graphene diffraction dynamics are genuine ultrafast electron intraband dynamics rather than optical interference artifacts. The reply argues that the attosecond optical gating provides true temporal resolution with a 625-as gate window, that ungated electrons are blind to the dynamics and can be subtracted as background, that shadow-region and low-power control measurements rule out optical artifacts, and that the term 'attosecond electron microscopy' is appropriate for diffraction-mode TEM. The central claim is that Hui et al. constitutes the first realistic demonstration of attosecond imaging resolution in electron microscopy.

Significance. If the central claim were fully substantiated, this reply would defend a high-impact result: the first demonstration of attosecond temporal resolution in an electron microscope in imaging/diffraction mode, distinct from pulse-train or continuous-wave approaches. The manuscript has some genuine strengths: the shadow-region subtraction is a reasonable check on background contamination, the low-power control is a relevant falsification test, and the point that artifact signals would scale with background oscillations is a useful argument. However, the reply does not provide a quantitative characterization of the optical gate transfer function, and several load-bearing assertions are either unmeasured or speculative. The paper currently does not establish the 625-as gate window or the claimed signal isolation, so its significance is conditional on additional evidence.

major comments (4)
  1. [Section 2] The claim that the leading and trailing circularly polarized evanescent fields of the optical gating pulse 'cancel each other out when integrated on the mesh' is asserted without a quantitative derivation, simulation, or control measurement. The statement that the two fields are 'separated in time by π' does not by itself establish that the transmitted electron fraction is confined to a 625-as window. Because the 0.2% gated-electron fraction and the estimated 5,000 gated electrons per image in Section 4 are both derived from this assumed gate width, the temporal-resolution claim and the signal-to-noise estimate are unsupported if the cancellation is incomplete, asymmetric, or contaminated by the circular components. A measured or simulated gate transfer function, or an independent streaking or energy-domain characterization of the gated electron pulse, is needed.
  2. [Section 4] The explanation that the gated portion of the beam 'may amplify coherence and spatial focusing effects' is a speculative post hoc mechanism and is not quantified. Absent a model or measurement of such amplification, the observed diffraction signal cannot be reconciled with a 0.2% gating fraction. In addition, the same section states that 'we did not interpret the quantitative diffraction oscillation amplitude,' so the reply does not provide a quantitative comparison between the measured signal and a modeled intraband-dynamics response. Both omissions weaken the central claim that the observed oscillations are genuine gated dynamics rather than an averaged or artifact-related response.
  3. [Section 3] The shadow-region subtraction and the low-power control are useful tests, but the figures and the text report no error bars, no statistical tests, and no repeatability information. The statement that the background modulation has 'minimal amplitude' compared with the diffraction peaks is therefore not quantitatively supported. The low-power control at 1.75 V/nm shows an absence of signal, but it does not constrain the temporal width or contrast of the optical gate itself, so by itself it cannot refute the Baum-Ropers artifact hypothesis. Quantitative uncertainties and a direct gate characterization would be required to make this control decisive.
  4. [Section 1] The premise that ungated electrons are 'blind' to the pump-induced dynamics and can be treated as background noise and subtracted is stated without direct experimental evidence. If the ungated portion of the electron pulse also experiences pump-induced deflection, energy modulation, or space-charge effects, the subtraction could either remove real signal or introduce a false one. This assumption is load-bearing for the isolation of the gated signal, and it is not tested by the controls described in Section 3, which address optical background rather than the response of the ungated electron population.
minor comments (5)
  1. [Section 2] The phrase 'separated in time by π' is ambiguous; it should specify whether this means π radians of the optical carrier cycle or a physical time interval, and it should be accompanied by the corresponding numerical value in attoseconds.
  2. [Section 4] The sentence 'to avoid any interruption duration the data acquisition' is ungrammatical and should be revised to 'to avoid any interruption during the data acquisition.'
  3. [Section 5] There is a typo in 'in in Hui et al.' that should be corrected.
  4. [Section 1] The statement that the authors of reference (2) 'are not providing raw data (only processed data)' is presented without specific documentation and is not a scientific argument; it should be removed or supported with concrete details about which data are unavailable.
  5. [Figures 1-3] The figure descriptions mention smoothing lines and dashed lines, but the text-only version does not show the actual figure panels; the final version should include complete panels with labeled axes, units, and uncertainty estimates so the claimed comparisons can be independently evaluated.

Circularity Check

2 steps flagged · score 6.0 of 10

The reply's central gating argument is self-referential: ungated electrons are defined as blind, the 625-as gate window is asserted rather than measured, and the small 0.2% gated-electron estimate is reconciled with the observed signal only by an untested coherence-amplification term.

  1. self definitional [Section 1, 'Addressing the Claim of “Lack of Electron Gating”']
    "The gated electrons in our setup, still capture the relevant dynamics, and the ungated electrons can be treated as background noise since they are blind to these dynamics and can be subtracted to isolate the dynamics of interest. This is the method we employed in Hui et al. (4)."

    This sentence defines the subtraction procedure in terms of the conclusion: electrons that produce the claimed signal are labeled 'gated' and electrons that do not are labeled 'blind' and subtracted. The only citation provided for this method is Ref. 4, the very paper whose conclusion is under dispute. No independent gate-transfer measurement establishes that the ungated electrons are unaffected by the pump, so the residual signal after subtraction is equivalent to the assumed gated signal by construction. The later shadow-region and low-power controls constrain background modulations, but they do not calibrate the temporal contrast or width of the optical gate, leaving the definitional identification load-bearing.

  2. fitted input called prediction [Section 4, 'Addressing the Unrealistic Signal and Noise Levels']
    "The gating time window, however, is 625 attoseconds. Consequently, only 0.2% of the electron beam (assuming a Gaussian distribution of the main electron pulse) is gated, with an estimated 5,000 gated electrons per image out of a total of 2.5 million electrons per image. This is sufficient for probing dynamics and our results averaged over seven scans. Regarding the signal amplitude, the laser pulse gating the electrons may amplify coherence and spatial focusing effects on the gated portion of the beam."

    The 0.2% estimate is derived from the very 625-as gate-window claim that is the central point in dispute. When that small fraction appears inconsistent with a detectable diffraction signal, the reply invokes unmeasured 'coherence and spatial focusing effects' to close the gap. No calibration, simulation, or control measurement characterizes the gate transfer function or the gated-electron fraction as a function of time. The observed signal is thus used to confirm that the 0.2% gating is sufficient, while any shortfall is absorbed by an adjustable amplification term. 'Sufficiency' is therefore not predicted from independent parameters; it is asserted after the fact to make the original observation compatible with the assumed gate.

full rationale

The reply is not entirely without independent content: the shadow-region comparison and the low-pump-power control are self-contained checks that background optical interference is not the main source of the diffraction dynamics. Those controls, however, test contamination of the measured signal, not the temporal resolution of the optical gate. The 625-as gate window, the cancellation of the leading and trailing circularly polarized fields, and the blindness of the ungated electrons are all asserted rather than demonstrated, and the only prior-work citation used to support the subtraction method is the authors' own Ref. 4. The Section 2 statement that the circular parts of the OGP 'effectively cancel each other out' is a load-bearing premise, but it is an unverified assumption rather than a reduction of one equation to another, so it is not counted as a separate circular step. Together, the definitional subtraction and the post hoc coherence-amplification argument mean that the central claim that the observed dynamics are genuine attosecond electron motion reduces, in part, to the assumptions used to define the gating. Because the reply does offer some independent control measurements, the circularity is partial rather than total, giving a score of 6.

Assumptions & free parameters 2 free parameters · 4 assumptions · 0 invented entities

The reply relies on several unverified or lightly supported assumptions about the experimental mechanism. The most significant are the blindness of ungated electrons and the cancellation of circularly polarized fields, both of which are asserted rather than demonstrated. No new physical entities are introduced.

free parameters (2)
  • Estimated electron pulse duration = ~300 fs
    Used to argue that only 0.2% of the electron beam is gated. This value is from 'classic space-charge calculations' and is not directly measured in this reply, so the gating fraction and the sufficiency of 5000 gated electrons depend on it.
  • Gating time window = 625 attoseconds
    Stated as the design parameter of the optical gating pulse. The ratio of this window to the 300 fs pulse duration underpins the 0.2% gating fraction.
assumptions (4)
  • domain assumption Ungated electrons are blind to the pump-induced dynamics and can be subtracted as background noise.
    Invoked in Section 1 to justify background subtraction. No experimental evidence in this reply directly demonstrates that ungated electrons do not respond to the pump field.
  • ad hoc to paper The leading and trailing circularly polarized evanescent fields from the optical gating pulse cancel on the mesh, leaving only the linear portion's plasmon field.
    Stated in Section 2 without mathematical derivation or supporting measurement. The gating mechanism relies on this cancellation, making it load-bearing.
  • domain assumption The carrier population in graphene increases nonlinearly with field strength, so no signal appears at 1.75 V/nm but appears at 2.4 V/nm.
    Used in Section 3 to explain the low-power control result. This is a plausible physical assumption but is not quantified or directly measured in this reply.
  • domain assumption The Debye-Waller effect acts on picosecond timescales, much longer than the measurement window.
    Invoked in Section 3 to reject the Debye-Waller explanation for diffraction order scaling. This is standard knowledge, but the exact timescale for the specific conditions is not discussed.

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Cite this review

Pith. "Pith review of Comment on "Comment on Attosecond electron microscopy and diffraction"." pith.science (2026). https://pith.science/paper/62CELWGU

@misc{pith2026250206592,
  author       = {Pith},
  title        = {Pith review of: Comment on "Comment on Attosecond electron microscopy and diffraction"},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/62CELWGU}},
  note         = {Machine review of arXiv:2502.06592}
}
read the original abstract

Over the past few decades, following the first demonstration of ultrafast electron microscopy, numerous research groups have focused on achieving attosecond temporal resolution in electron microscopy with the goal of imaging electron and atomic motion. Recently, several studies have claimed to achieve attosecond temporal resolution in imaging(1-3). These claims are based on the generation of attosecond electron pulse trains. However, in typical time-resolved measurements used to capture dynamic processes in real-time, the temporal resolution is determined by the envelope of the pulse train. The reliance of using attosecond electron pulse trains fails to account for the distinct temporal resolution advantages enabled by our attosecond optical gating, which are absent in the case of using a continuous-wave or long laser pulse. These oversights highlight the limitations of this methodology (1-3) in studying ultrafast phenomena of matter. It is crucial to clarify this distinction to avoid confusion, misinterpretation, and potential miscitations within the community regarding attosecond temporal resolution in electron microscopy and the attosecond imaging of matter dynamics. In contrast, Hui et al. (4) present the first realistic demonstration of attosecond imaging resolution in electron microscopy, enabling the diffraction imaging of electron motion dynamics in graphene. In a commentary by Peter Baum and Claus Ropers, the authors conjecture that the graphene dynamics observed in our time-resolved diffraction experiment (Fig. 5, Hui et al. 2024) (4) is an optical interference artifact or light modulation of electrons effects, similar to what was reported previously (1-3), in addition to raising other technical concerns. In this reply, we are pleased to address these allegations and provide clarifications to resolve the raised technical questions.

Figures

Figures reproduced from arXiv: 2502.06592 by the authors.

Figure 1
Figure 1. The measured diffraction dynamics signals for (from top to down) the 1st-, 2nd-, and 3rd-order peaks are shown as black dots connected by a dashed black line (as presented in [PITH_FULL_IMAGE:figures/full_fig_p004_1.png] view at source ↗
Figure 2
Figure 2. The measured diffraction dynamics signals for [PITH_FULL_IMAGE:figures/full_fig_p004_2.png] view at source ↗
Figure 3
Figure 3. The measured diffraction signals for (from top to down) the 1st-, 2nd-, and 3rd-order diffraction peaks, pumped by a low-intensity laser pulse, are represented as black dots connected by a dashed black line. These signals are compared to the background modulation signals: (1) from the shadow regions adjacent to the 1st-, 2nd-, and 3rd-order diffraction peaks (blue dashed line), and (2) from [PITH_FULL_IMAGE:figures… view at source ↗

Discussion (0). Continue with ORCID to comment.

Reference graph

Works this paper leans on

11 extracted references · 9 canonical work pages

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    Lack of Electron Gating

    Addressing the Claim of “Lack of Electron Gating” The first presumption by the Baum and Ropers, “Lack of electron gating”, is based on authors’ statement “Modulation without filtering is not gating”. However, this reasoning is fundamentally flawed. The inability to detect directly a phenomenon due to a lack of the desired tools does not imply that the phe...

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    D. Hui, H. Alqattan, M. Sennary, N. V. Golubev, M. T. Hassan, Attosecond electron microscopy and diffraction. Science Advances 10, eadp5805 (2024)

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    Attosecond Electron Microscopy

    Terminology Debate: “Attosecond Electron Microscopy” Next, Baum and Ropers object to our use of the term "microscopy" in Hui et al. (2024) (4), where we referred to our experiment as attosecond electron microscopy ("attomicroscopy"). Their objection is based on their definition of microscopy, which they describe as "the production of magnified images of a...

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    For instance, we specified the optical focus diameter (~200 μm) on page 2 of Ref

    Lack of due diligence: Baum and Ropers seem to have overlooked critical details. For instance, we specified the optical focus diameter (~200 μm) on page 2 of Ref. 4, while the electron pulse beam size is ~80 μm. We also provided comprehensive data, including raw measurements and the integration times attached. Our electron pulse duration estimates between...

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    Sansone, E

    G. Sansone, E. Benedetti, F. Calegari, C. Vozzi, L. Avaldi, R. Flammini, L. Poletto, P. Villoresi, C. Altucci, R. Velotta, S. Stagira, S. De Silvestri, M. Nisoli, Isolated Single-Cycle Attosecond Pulses. Science 314, 443 (2006)

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    Morimoto, P

    Y. Morimoto, P. Baum, Attosecond control of electron beams at dielectric and absorbing membranes. Phys. Rev. A 97, 033815 (2018)

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    In this reply, we are pleased to address these allegations and provide clarifications to resolve the raised technical questions focusing on the published data on Hui et al

    (3), in addition to raising other technical concerns. In this reply, we are pleased to address these allegations and provide clarifications to resolve the raised technical questions focusing on the published data on Hui et al. (4), since M. Yuan, et. al., arXiv:2411.02731 (202...

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    (Nature Photonics 2024)(2), and Morimoto et al

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Reviewed August 8, 2026 · model on record in the stance chip above.