A Laser Damage Threshold for Microscope Glass Slides

Round 1

Reviewer 1 Report

This work is focused on the laser-induced damage threshold (LIDT) of high-quality microscope glass slides. As we know, LIDT is important for optics. However, it is hard to evaluate exactly for the uncertainty of laser parameters and the complex damage mechanisms. In this work, authors measured the all parameters of laser one pulse by one pulse, and analyze the data detailed. So the reliable and scientific statistical results were obtained. It also gives us a relative accuracy measurement and analysis methods for LIDT. I recommend to receive it.

 

There still some problems should be corrected before publishing.

1. In, figure 5 a), an obvious corrugation is presented, however it was not observed in other two pictures. In other hand, the damage spot in figure 5 c) is smaller and irregular than other two pictures. What is the reason?

2. The case such as “Laser-Induced Damage Threshold” is not same in total manuscript.

3.   In line 91, the writing of SiO2, Na2O is not correct.

4.  In line 301, the wavelength of laser is wrong.

Author Response

Dear Reviewer,

In the following pages, we reiterate recommendations and comments and respond accordingly as indicated. The paper was updated to address all of the suggestions made by the reviewers. Requested changes and newly added paragraphs were highlighted with yellow and green colours, respectively.
Grammatical and spelling errors were corrected where appropriate. Having this opportunity, I, on behalf of all authors, would like to thank you for the valuable comments and corrections

Yours sincerely,

Corresponding author,
Dr. Humbat NASIBOV

The authors have accepted all the comments and suggestions provided by the reviewers. 

 

Reviewer 1

Comments and Suggestions for Authors

This work is focused on the laser-induced damage threshold (LIDT) of high-quality microscope glass slides. As we know, LIDT is important for optics. However, it is hard to evaluate exactly for the uncertainty of laser parameters and the complex damage mechanisms. In this work, authors measured the all parameters of laser one pulse by one pulse, and analyze the data detailed. So the reliable and scientific statistical results were obtained. It also gives us a relative accuracy measurement and analysis methods for LIDT. I recommend to receive it.

1. In, figure 5 a), an obvious corrugation is presented, however it was not observed in other two pictures. In other hand, the damage spot in figure 5 c) is smaller and irregular than other two pictures. What is the reason?

Thank you for your valuable comment. The following paragraph was added to the text.

Figures 5 a) and b) show that the damage process is primarily dominated by thermal effects, especially for 1064 nm and 532 nm wavelengths, as evident from the observed damage craters, circular scalds, and terrace-like ablated structures. However, damage morphologies, such as cracks or fractures (mainly attributed to the laser-induced mechanical stress), were primarily observed in tests at 355 nm wavelength, as shown in Figure 5 c) and discussed in Section 4.

2. The case such as “Laser-Induced Damage Threshold” is not same in total manuscript.

         Thank you. Corrected and harmonized through the paper.

3. In line 91, the writing of SiO2, Na2O is not correct.

Corrected.

4. In line 301, the wavelength of laser is wrong.

Thank you. Corrected.

Thank you for all your comments!

Finally,

The following statement will be added to the Acknowledgements section.

The authors are grateful to anonymous referees for their useful comments and constructive suggestions. 

Reviewer 2 Report

Authors measured damage thresholds for different glass slides by three harmonics of a nanosecond Nd:YAG laser. The paper contains valuable information. I suggest to accept the manuscript after major revision.

 

Questions:

1.     What was the laser beam quality quantified by M2? Laser beam quality is a key parameter for measuring damage threshold so it is a key parameter for this paper. I didn’t found the description through the manuscript.

2.     Page 3. Line 137. Poor usage of the term “in situ”. According to the authors description the defects were quantified after laser pulse so it cannot be called “in situ”. It can be called “on line” or “on site” but not “in situ”. In such experiments “in situ” meant the measurement of the defect during the laser pulse interaction.

3.     Lines 230-231. Poor term usage. What is “the effective area and effective diameter”? Effective for what? How the authors defined the efficiency? Please skip the term “effective” here.

4.     Fig. 5 and Table 1. Strange results. Why laser beam waist is the smallest for the 1064 nm and largest for 355 nm laser beam. At lines 231-232 the authors blamed that “The measured and evaluated results of the beam diameter and effective area at the waist at 1/e2 are listed …”. The laser beam waist is defined at the location along the propagation direction where the beam radius has a smallest value. For the same focusing system the smallest beam waist will always get for the laser beam with the shortest wavelength i.e. the smallest for 355 nm and the largest for 1064 nm. This is due to the Abbe diffraction limit (d = wavelength/2*numerical_aperture). However, authors presented results which are in contradiction with that. Did the authors varied lens to sample distance to get the smallest laser spot (waist) at the sample surface?

5.     Fig. 7 wrong figure caption and title for ordinate axis. According to the text Fig. 7 is a histogram for the different craters rather than “An example of 3D profiles of damaged sites”. How “counts” can correspond to the units “um”? Please correct both problems.

6.     Lines 302-305. False discussion on laser craters diameters until laser beam waists were not accurately measured (see my question 5 above). The laser crater diameter and depth depends on numerous factors including the laser irradiance at the spot. For example, authors skipped discussion on difference in material absorption for different wavelengths.

7.     Some major papers on measuring laser induced damage are skipped in the introduction. I strongly recommend to read through these papers to improve the authors scientific level. Papers: 1) Liu, J. M. (1982). Simple technique for measurements of pulsed Gaussian-beam spot sizes. Optics letters, 7(5), 196-198; 2) Jee, Y., Becker, M. F., & Walser, R. M. (1988). Laser-induced damage on single-crystal metal surfaces. JOSA B, 5(3), 648-659. The mentioned papers were published 30 years ago but provided more sensitive and precise ways to quantify laser induced damage.

8.     Table 2. What are errors for LIDT? The authors presented numbers with three digits but didn’t provided the error. In such case one can assume that error is less than 0.1%. From the fig. 8 is obvious that LIDT errors is about of 10% of the value or more. Please, add the corresponding errors or description in the table 2 text or description.

9.     Poor English. Line 192. “to achieve low-uncertainty results ” It is better to use term “reliable results” in my opinion. 

Poor English. Line 192. “to achieve low-uncertainty results ” It is better to use term “reliable results” in my opinion. 

Author Response

Dear Reviewer,

In the following pages, we reiterate recommendations and comments and respond accordingly as indicated. The paper was updated to address all of the suggestions made by the reviewers. Requested changes and newly added paragraphs were highlighted with yellow and green colours, respectively.
Grammatical and spelling errors were corrected where appropriate.

Having this opportunity, I, on behalf of all authors, would like to thank you for the valuable comments and corrections

Yours sincerely,

Corresponding author,
Dr. Humbat NASIBOV

The authors have accepted all the comments and suggestions provided by the reviewers. 

Reviewer 2

Comments and Suggestions for Authors

Authors measured damage thresholds for different glass slides by three harmonics of a nanosecond Nd:YAG laser. The paper contains valuable information. I suggest to accept the manuscript after major revision.

1. What was the laser beam quality quantified by M2? Laser beam quality is a key parameter for measuring damage threshold so it is a key parameter for this paper. I didn’t found the description through the manuscript.

We agree that M2 is a key parameter and should be mentioned in the paper. A new column  M2  was added into Table 1, describing the M2 at each laser wavelength.

 

2. Page 3. Line 137. Poor usage of the term “in situ”. According to the authors description the defects were quantified after laser pulse so it cannot be called “in situ”. It can be called “on line” or “on site” but not “in situ”. In such experiments “in situ” meant the measurement of the defect during the laser pulse interaction.

       Thank you very much for the insight. Corrected through the paper.

3. Lines 230-231. Poor term usage. What is “the effective area and effective diameter”? Effective for what? How the authors defined the efficiency? Please skip the term “effective” here.

             We highly appreciate this comment.

1. The term “effective” was removed in Lines 230-231, as well as in Line 127 (where it was related to a diameter).
2. The following statements were added to the text after Lines 230-231.

At each wavelength the beam diameter  was assessed at the 1/e² width.  According to these results, the corresponding effective areas were calculated using the equation [7]:

. The calculated beam diameters and effective areas of the spot on the sample are listed in Table 1.

 

4. 5 and Table 1. Strange results. Why laser beam waist is the smallest for the 1064 nm and largest for 355 nm laser beam. At lines 231-232 the authors blamed that “The measured and evaluated results of the beam diameter and effective area at the waist at 1/e2 are listed …”. The laser beam waist is defined at the location along the propagation direction where the beam radius has a smallest value. For the same focusing system the smallest beam waist will always get for the laser beam with the shortest wavelength i.e. the smallest for 355 nm and the largest for 1064 nm. This is due to the Abbe diffraction limit (d = wavelength/2*numerical_aperture). However, authors presented results which are in contradiction with that. Did the authors varied lens to sample distance to get the smallest laser spot (waist) at the sample surface?

We agree with you and your discussions. In the initial system with a single lens we adjusted the spot size on the sample surface by just varying the distance between the lens and the surface. In the current system we used a combination of lenses to have more or less same order of the spot size in the focal plane. A combination of lenses under the hand in the laboratory allowed us to have spot sizes shown in Table 1. The related part of the text was reworked as follows, with adding new statements highlighted in green:

A couple of flat mirrors (M1 and M2, Figure 1) were used to adjust the laser beam onto a focusing element. The focusing element, comprising a combination of several lenses fixed on a computer-controlled linear stage, was used to focus the laser beam onto the surface of the specimen. For each harmonics of the laser a different set of mirrors and lenses with appropriate to that wavelength coatings was used. So, by the changing the lenses and the distance between them, the configuration of the focusing element is adjusted for each wavelength individually. The computer-controlled linear stage, with a traveling distance of 30 cm, is used to move the whole focusing element along the optical path with respect of sample surface. To obtain accurate measurement results, the sample surface was positioned at the focal point with an accuracy of less than one Rayleigh length [22,23].

 

 

5. 7 wrong figure caption and title for ordinate axis. According to the text Fig. 7 is a histogram for the different craters rather than “An example of 3D profiles of damaged sites”. How “counts” can correspond to the units “um”? Please correct both problems

Thank you very much for this comment. Corrected and reworked accordingly.

1. “um” was changed by “counts”
2. The figure caption is replaced with: “The histograms of the damage diameter distributions”.

 

6. Lines 302-305. False discussion on laser craters diameters until laser beam waists were not accurately measured (see my question 5 above). The laser crater diameter and depth depends on numerous factors including the laser irradiance at the spot. For example, authors skipped discussion on difference in material absorption for different wavelengths.

We agree with the discussion “The laser crater diameter and depth depends on numerous factors including the laser irradiance at the spot.”

However, we can definitely say that two parameters, the laser output energy and the laser beam diameters were measured (and on-line monitored) with a grate accuracy. Laboratory has a more than 10 years’ experience on that. (It is worth to note here that the beam waists (including the M2 and the Rayleigh length) were measured in two different methods, as mentioned in the paper by means of the camera based beam profiler, as well as by using a detection system with a mechanically moving knife-edge head. The discrepancy between results were less than 0.6%.)

Regarding the relation between the spot size and the crater diameters: literature and our experience, as well, show that when the thermal effects dominate in the damage creation, then there is a correlation between them. It becomes more complicated when cracks are formed due to mechanical stresses (especially at higher fluences). This part is reflected in the paper well.

Regarding the “discussion on difference in material absorption for different wavelengths.” The following paragraph was added to the discussion Section.

 

Morphological observations revealed that, aside from infrequent color changes on the sample surface, which are more common in the 355 nm tests, a fatigue damage mechanism was observed across all samples. The damage morphology clearly illustrates that at longer wavelengths, prevailing damages exhibit crater-like patterns with central holes and diameters smaller than the beam diameter. In contrast, at 355 nm, the damage morphology differs significantly, featuring primarily shallow cracks or fractures (largely attributed to laser-induced mechanical stress) rather than the smoother profiles associated with crater-type damages. Typically, within the nanosecond laser pulse range, failures of bulk material components originate from impurities, defects, and inclusions.

During the initial laser pulses, these sources initiate small damage sites due to pronounced energy absorption and field intensification. These smaller initial damages, when exposed to additional laser irradiation, lead to an expansion of the affected area. The process, referred to as "damage growth" [for example, 33,34], involves subsequent laser pulses with sufficient fluence that re-ignite the initial damage sites. Energy is then deposited around this region, heating these local centers and resulting in a significant temperature gradient and a high-pressure environment (in contrast to the uniformly adjusted areas). These mechanical and thermodynamic effects lead to micro-explosions, material melting, fragmentation, and generation of cracks in the material [35].

It has been demonstrated [34] that damage growth, akin to the damage initiation process, is influenced by factors including laser fluence and wavelength, as well as pulse duration and shape, the types of input and output surfaces, whether in air or vacuum. Recently, a robust correlation has been established between subsequent damage growth and the sizes (lateral size and vertical depth) and morphology of the initial damage sites [36]."

As demonstrated in reference [15], the initial damage structures and morphologies exhibit a correlation with the laser wavelengths. A comparative investigation [36], contrasting the impact of 532 nm and 1064 nm laser irradiation, revealed distinct characteristics in initial damage sites and subsequent damage growth. Specifically, 532 nm laser irradiation led to the formation of numerous small craters, whereas under 1064-nm laser irradiation resulted in individual, large-sized, and deeper craters.

Moreover, a strong correlation has been found between the absorption coefficient of the defects and the laser-induced damage threshold of the surface, determining the damage morphologies [34,36]. The defects' absorption coefficient strongly depends on the wavelength of the absorbed light. At shorter laser irradiation wavelengths, the higher photon energies and enhanced absorption effects of impurities and defects result in the rapid formation of damage structures. These include scattered small initial damage craters and material evaporation. Furthermore, as demonstrated in [15,33], the use of 355 nm laser irradiation produces a distinct damage morphology characterized by scattered, small, and shallow craters, a consequence of dispersed absorptive defects. Even with increased fluence, the laser energy is directed toward the rapid generation of numerous dispersed damage sites. This occurs before the individual sites undergo further growth, eventually encompassing the area of the laser beam. In contrast, the formation of macroscopic damages, such as large-scale craters and cracks, necessitates the substantial accumulation and subsequent release of thermal and mechanical stress.

Our findings across all tested samples and wavelengths exhibit a consistent pattern. With the exception of the 532 nm damage morphology, characterized by the predominance of single crater-like damages followed by the formation of numerous small craters (as observed in high-purity fused silica-based optical glasses [36]), the damage morphology at the other two wavelengths closely aligns with the descriptions above and in the literature. Our findings also confirm that when applying short wavelengths for UV applications, predominantly smaller inclusions and impurities with higher damage precursor densities will cause damage, as was observed for the damage at 355 nm.

 

 

7. Some major papers on measuring laser induced damage are skipped in the introduction. I strongly recommend to read through these papers to improve the authors scientific level. Papers: 1) Liu, J. M. (1982). Simple technique for measurements of pulsed Gaussian-beam spot sizes. Optics letters, 7(5), 196-198; 2) Jee, Y., Becker, M. F., & Walser, R. M. (1988). Laser-induced damage on single-crystal metal surfaces. JOSA B, 5(3), 648-659. The mentioned papers were published 30 years ago but provided more sensitive and precise ways to quantify laser induced damage.

We read both paper carefully and found them very valuable. Both papers are addressed in the text and added into the reference list. The following statements were added to the text.  “Absolute calibration of laser-energy fluences is essential for quantitative studies of LIDT. The accuracy of this calibration, along with the energy of a typical pulse, depends primarily on the measurement of the laser-beam spot size [].”

 

8. Table 2. What are errors for LIDT? The authors presented numbers with three digits but didn’t provided the error. In such case one can assume that error is less than 0.1%. From the fig. 8 is obvious that LIDT errors is about of 10% of the value or more. Please, add the corresponding errors or description in the table 2 text or description.

         Thank you very much for pointing out this omission. The table was reworked accordingly.

3. The statement, “….summarized in Table 2, where the standard deviations describe the distribution of the calculation results. The total measurement uncertainty is presented in Section 3.2.3.” was added.
4. Table 2 caption was corrected as: “The average LIDT values and the standard deviations of three samples for the zero percent damage probability.”

 

9. Poor English. Line 192. “to achieve low-uncertainty results ” It is better to use term “reliable results” in my opinion. 

Corrected.

Thank you for all comments!

 

Finally,

The following statement will be added to the Acknowledgements section.

 

The authors would like to thank the anonymous referees for useful comments and constructive suggestions.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

Authors makes significant improvement of the manuscript but minor improvement is still required (check the questions below).

I suggest to accept the manuscript after minor revision.

Questions:

1.     Lines 239-242. Still the problem with the terms “the effective area and effective diameter”. The efficiency should be defined in the text. For example, the efficiency of laser ablation can be defined ablated material mass divided by laser pulse energy so the most efficiency ablation corresponds to the maximum ratio.

2.     Line 239. Poor term usage. “… measure the diameter of a "typical pulse" on the focal plane ...” There is no diameter for the pulse. Use term “laser beam” or “beam” instead of “typical pulse”.

3.     Lines 127-128. “To obtain accurate measurement results, the sample surface was positioned at the focal point with an accuracy of less than one Rayleigh length”. This is very poor accuracy of the lens-to-focal distance. Rayleigh length is defined as the distance from the beam waist (in the propagation direction) where the beam radius is increased by a factor of the square root of 2. In other words, you cannot precisely measure the Laser-Induced Damage Threshold with such poor accuracy of lens-to-sample distance.

Author Response

Dear Reviewer,

 

Thank you once again for all comments. All suggestions are accepted by the authors. The corresponding corrections are done and highlighted in yellow and green in the resubmitted manuscript.

 

• Lines 239-242. Still the problem with the terms “the effective area and effective diameter”. The efficiency should be defined in the text. For example, the efficiency of laser ablation can be defined ablated material mass divided by laser pulse energy so the most efficiency ablation corresponds to the maximum ratio.

 

 The abovementioned terms are removed from the text through the paper.

 

• Line 239. Poor term usage. “… measure the diameter of a "typical pulse" on the focal plane ...” There is no diameter for the pulse. Use term “laser beam” or “beam” instead of “typical pulse”.

 

Thank you very much for the comment. Corrected.

 

• Lines 127-128. “To obtain accurate measurement results, the sample surface was positioned at the focal point with an accuracy of less than one Rayleigh length”. This is very poor accuracy of the lens-to-focal distance. Rayleigh length is defined as the distance from the beam waist (in the propagation direction) where the beam radius is increased by a factor of the square root of 2. In other words, you cannot precisely measure the Laser-Induced Damage Threshold with such poor accuracy of lens-to-sample distance.

 

We highly appreciate this comment. Thank you very much, indeed.

The translation system allowed the precise positioning of the sample surface at the focal point, achieving an accuracy of ± 1.25 mm. This level of accuracy exceeds one order of magnitude compared to the Rayleigh length corresponding to each wavelength.

.

 

 

Author Response File: Author Response.docx