A Contrast Calibration Protocol for X-ray Speckle Visibility Spectroscopy
, Vincent Esposito 1, Philip Adam Hart 1, Conny Hansson 1, Haoyuan Li 1,2, Kazutaka Nakahara 1, James Paton MacArthur 1, Silke Nelson 1, Takahiro Sato 1, Sanghoon Song 1, Peihao Sun 1,2, Paul Fuoss 1, Mark Sutton 1,3 and Diling Zhu 1,*Round 1
Reviewer 1 Report
Dear authors, thank you for submitting your manuscript. It reads easily, is well organised and demonstrates for a serious methodology. It was appreciated that both the influences of the source and of the detector were taken into account. No revisions required.
Author Response
We thank the reviewer for the supportive summary.
Reviewer 2 Report
The referee’s report is summarized in the attached document.
Comments for author File: 
Comments.pdf
Author Response
We thank the reviewer for the supportive summary. Attached is our response.
Author Response File: Author Response.pdf
Reviewer 3 Report
The submitted manuscript compares three different methods for evaluating contrast from insufficient speckle-generated data on an ePix detector, unique to LCLS, to data generated by measuring contrast with the aid of a mask that eliminated cross-talk between different pixels. The method provides a start to evaluating contrasts that could be useful for on-the-fly analysis, though it admits that it does not completely retrieve the contrast evaluation from low signals, though it is a good start.
Though the manuscript is very specific, applicable to only a set of experiments only conducted at LCLS, and only conducted with the ePix detector, they occur often enough that the article is an appropriate topic for publication in this journal. However, some issues became obvious during the reading of the article that need to be addressed before it is to be published. The issues do not have to do with the basic premise of the article, but mainly with its execution and presentation.
- The article does not adequately explain the symbols and representations of the formulas it uses. There is never an explanation of what M is in the definition of contrast (β), k, and equation 1 presents P(k) while the following sentence talks about p(k). Are they the same parameter? If so, why are they not written the same way? The symbol N obviously means the number, but it is not defined. In fact, most of the symbols used in the equations are not properly defined, and need to be for a serious scientific publication.
- Figure 1 has several issues. The green square in 1(a) is almost impossible to see, and I recommend the authors use a thicker border and a brighter color to offset it from the near black background. Figure 1(d) seems odd and superfluous, as it has nothing to do with the experimental data shown in 1(a), 1(b), or 1(c). Nothing in 1(d) is necessary to the paper, as most of the relevant information for modelling and evaluation is shown in figure 2.
- The text should mention that the GG and LSF method used the same photon count distribution. It is easy to miss this in figure 2.
- Figure 3(c) has a very large vertical scale for a plot that is very close to zero. It would be helpful to reduce this so one could see the points more clearly. Figure 3(e) offers no explanation for what sigma means, and I could not find an explanation in the text. This needs to be corrected.
- The conclusion needs to elaborate a bit more. Though the paper has shown that the GG method is the best one for the ePix detector, could this protocol be used for other similar detectors, and with a similar mask-and-check approach? Could this be generalized to a larger set of experimental setups in other facilities, or is it specific to just this one instance? A short discussion on this topic would be very welcome. Also, the authors could comment if 1% level of accuracy is sufficient to make the sort of on-the-fly decisions that need to be made during an experiment.
Author Response
We thank the reviewer for the comment and support. We note that while the data presented was using the ePix100 detector at LCLS, the concept and methodology is universal and generally applicable to x-ray detectors used for visibility spectroscopy and XPCS experiments at most currently operating FEL facilities. It can be relevant for visibility spectroscopy measurements at synchrotrons as well. Attached is our response to the questions.
Author Response File: Author Response.pdf
