Thickness Measurement for Glass Slides Based on Chromatic Confocal Microscopy with Inclined Illumination

Round 1

Reviewer 1 Report

Dear authors,

Congratulation on your article. It is good research on a relevant topic. There are a few comments I would like to make:

1. Paraxial approximation: in your article you are constituently using the quantity a/f, which is the radius of the exit pupil over the focal length of the lens. Note, that this is a paraxial approximation for the NA, which would otherwise would be NA = sin(theta), with theta the angle between the marginal ray and the optical axis. Using this approximation is ok, but you should clearly state, that this approximation is valid for small angles (and preferably small should be defined).
2. The proposed advantage is, that the new configuration is more light efficient. It would be appreciated, if this statement could be quantified. Compared to standard chromatic probe sensor, one could assume a beam splitter ratio and argue from there. The second advantage is that under a steeper angle, the reflection off a surface is increased. For the chosen angle of 39deg that should be quantified as well, compared to ~4% at perpendicular incidence. In that context a short note on polarization should be added as well.

• The setup described is in fact a triangulation sensor with a chromatic probe added. The word triangulation sensor should be mentioned in the introduction, since this sensor type is well researched.

Some other details can be found in the attached pdf.

Comments for author File: Comments.pdf

Author Response

Dear reviewer:

Many thanks to your valuable comments.

In the responses, the parts with black font are the original comments, and the parts with red font are our replies to the corresponding comments. In the manuscript, we underlined and made annotations in the appropriate places. For convenience, we have also prepared a manuscript in PDF, which corresponds exactly to the contents in Word.

Thank you for your cooperation, and we hope to hear from you soon.

Best regards

Qing Yu

Author Response File: Author Response.pdf

Reviewer 2 Report

It is an interesting paper on on thickness measurements using optical methods. The presented idea is an improvement on the methods used so far. I support publishing this paper subject to some corrections:

How do the described methods compare with ellipsometry? This would be worth addressing in introduction and discussion of results.

Fig.8 What is the light source used in this setup?

Two paragrapghs starting from line 317: Fig.8 seems to be confused with Fig.9 there

Fig.13 Picture overlaps with text

Could the authors state the range of applications of the proposed method: what is the range of thickness that the method can measure accurately, what materials, what attenuation range, refractive index range. Is the method sensitive to the surface quality? Such text would be helpful in discussion of the results and an extract of it in conclusions.

Author Response

Dear reviewer:

Many thanks to your valuable comments.

In the responses, the parts with black font are the original comments, and the parts with red font are our replies to the corresponding comments. In the manuscript, we underlined and made annotations in the appropriate places. For convenience, we have also prepared a manuscript in PDF, which corresponds exactly to the contents in Word.

Thank you for your cooperation, and we hope to hear from you soon.

Best regards

Qing Yu

Author Response File: Author Response.pdf

Reviewer 3 Report

The manuscript by Qing YU et. al. reports about a method of a confocal-like thickness measurement for transparent samples using a white light laser and a color camera. The method might be of interest to certain industrial applications for quality control, among others.

 

The manuscript in general is well written, although it would benefit from a proof-reading of a native English speaker, as many sentences are constructed using structures which are not really typical for the English language. Figures of the manuscript are in general of good quality, but the figure captions are extremely short and should be extended. Even the sub-figures, e.g. (a)-(b), are not mentioned in the captions.

The manuscript would benefit from a more clear description of the limitations of the described method – what are the thinnest and what are the thickest structures it can measure? Also please describe what influences the limits and how they can be either extended in width, or shifted among scales.

It would be interesting to discuss the requirement of transparency of the samples, as no quantitative metric of the transparency is given – e.g. “the method is expected to work for samples with transmission of XX-YY%, but it was tested only on samples with the transmission of ZZ%”.

It is not completely clear to me if the color detection scheme used by the authors is critical for the success of the method. If the monochrome camera would be used for the detection, would it not be sufficient to use the distance between two reflections as the metric for calculation of the thickness?

The authors discuss the measurement error and the repeatability of the method, lines 412 + 429, but it’s not clear if the values are calculated from the average of the 40 repetitions of the method or from a single measurement? The errors and repeatability from a single measurement are way more important to report. Also, it would be interesting to include the required measurement time, which is of cause sample/system specific – but at the moment I did not see any quantitative information about the speed. Please also discuss the limits and ways for improvement of the speed.

Conclusions in the current version of the manuscript are more qualitative, e.g. “and the repeatability was good” but they need to be more quantitative, e.g. “and the repeatability of XY was achieved in YZ measurement time” or so.

Author Response

Dear reviewer:

Many thanks to your valuable comments.

In the responses, the parts with black font are the original comments, and the parts with red font are our replies to the corresponding comments. In the manuscript, we underlined and made annotations in the appropriate places. For convenience, we have also prepared a manuscript in PDF, which corresponds exactly to the contents in Word.

Thank you for your cooperation, and we hope to hear from you soon.

Best regards

Qing Yu

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Thank you for responding adequately to the suggestions made earlier. I would recommend one last check on the figures: labels of the axis, and labels of the components shown in the overview sketches.