Brief communication: Ambient-pressure femtosecond laser ablation as a solid-phase sampling method for water ice

Nielsen, Robin Vinther; Bertsia-Kanatouri, Ioanna; Peensoo, Kerttu Maria; Fassel, Simon Alexander Munk Wael; Malegiannaki, Eirini; Gkinis, Vasileios

doi:10.5194/egusphere-2026-4182

Preprints

https://doi.org/10.5194/egusphere-2026-4182

Preprints

30 Jul 2026

| 30 Jul 2026

Brief communication: Ambient-pressure femtosecond laser ablation as a solid-phase sampling method for water ice

Robin Vinther Nielsen, Ioanna Bertsia-Kanatouri, Kerttu Maria Peensoo, Simon Alexander Munk Wael Fassel, Eirini Malegiannaki, and Vasileios Gkinis

Abstract. High-resolution ice-core analysis requires sampling methods that preserve millimeter to sub-millimeter spatial information. We evaluate ambient-pressure femtosecond laser ablation (fs-LA) as a solid-phase and geometry-tolerant sampling method for water ice under cold, dry laboratory conditions. At 35 µJ and 50 kHz, visible localized craters were produced at all tested exposure times, with mean inner diameters of approximately 87–165 µm. Crater formation was repeatable at a 0.5 mm pitch along 400-position scan paths. The 1 s exposure produced the smallest sampling footprint and largest fraction of craters without visible rims, supporting fs-LA as a platform for future cryospheric analyses.

Received: 13 Jul 2026 – Discussion started: 30 Jul 2026

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Robin Vinther Nielsen, Ioanna Bertsia-Kanatouri, Kerttu Maria Peensoo, Simon Alexander Munk Wael Fassel, Eirini Malegiannaki, and Vasileios Gkinis

Status: final response (author comments only)

RC1:
'Comment on egusphere-2026-4182', Anonymous Referee #1, 02 Sep 2026
The work “Ambient-pressure femtosecond laser ablation as a solid phase sampling method for water ice” presents a fundamental evaluation of the crater morphology upon the ablation of Mili-Q water ice with a novel ambient pressure femtosecond laser ablation unit. The work aims to assess crater morphology by visually inspecting the rim generated by the interaction between the laser and the ice sample. Although interesting I consider this work need a substantial amount of work to be completed and I consider major revision is needed.
The characterization of crater morphology currently relies primarily on optical images and the determination of the inner crater and rim-to-crater diameters. While these parameters provide useful initial information, they may not be sufficient to fully describe the laser-sample interaction. Additional parameters, such as ablation depth and the reproducibility of crater dimensions among replicate ablation spots, would provide a more comprehensive assessment of the ablation process and strengthen the conclusions regarding the performance and robustness of the method.

The generated craters and the consequent rims are generated at fixed energy and spot size conditions by just changing the exposure time between 1 and 16 seconds. The work would greatly benefit from a more general analysis including more experimental parameters.

The rim generated upon the ablation of ice is assessed visually and the authors refer to the rim as a consequence of processes such as refreezing, sublimation, condensation and redeposition. Is there any other quantitative metric that could help to understand when is the rim generated?

I recommend to include Appendix D in the main manuscript due to its relevance in the discussion and overall understanding of the work.

The authors state that the ablated material could be coupled to different detection techniques. While this is an interesting perspective, the manuscript does not provide experimental evidence regarding key aspects required for successful downstream analysis of ice samples, such as elemental fractionation, refreezing or sublimation effects, and the reproducibility of the ablation process. As these factors can significantly influence the suitability of the generated aerosol for subsequent analytical measurements, a more detailed discussion of these limitations and/or supporting evidence would strengthen this claim.

The work would benefit significantly from the inclusion of a proof-of-concept study involving natural ice samples, as this would provide a more realistic demonstration of the applicability of the proposed approach. In this context, and as acknowledged by the authors, a more comprehensive evaluation of parameters such as ablation yield, crater morphology, and potential material redistribution processes would further strengthen the manuscript and help assess the performance of the method under representative conditions.
Citation: https://doi.org/10.5194/egusphere-2026-4182-RC1
RC2:
'Comment on egusphere-2026-4182', Anonymous Referee #2, 10 Nov 2026
This brief communication assesses the suitability of a 1030 nm wavelength femtosecond (fs) pulse duration laser ablation (LA) setup for sampling material from solid ice samples. The study focuses on crater morphology as an indicator of sampling quality, and analyses the optical appearance of craters collected under different exposure times. Based on this analysis, the system creates craters with predictably distributed sizes, increasing in diameter with increased exposure time.
I recommend the manuscript to be published subject to major revisions. The manuscript is generally well written, and would benefit primarily from making the motivation behind using this new setup, and the choice of analysis, clearer.
The manuscript links the sample cell geometry to the choice of laser, for example on L30 “Ambient-pressure fs-LA may therefore offer a geometry-tolerant route to localized solid-phase sampling”, or L2-3 “We evaluate ambient-pressure femtosecond laser ablation (fs-LA) as a solid-phase and geometry-tolerant sampling method”. This link needs to be explained. Is the choice of laser dependent on the sample chamber? Could a similar setup be established (with appropriate optics) for a nanosecond laser? If not why not?

The use of a fs laser is stressed in the manuscript. Other laser parameters, such as laser wavelength, are also important. L20-26 notes that past studies have used different laser types for LA, and notes only that sample geometry was a limitation. With other studies using 157 nm or 193 nm lasers for impurity measurements, a short discussion with a few more recent references regarding choice of laser parameters could motivate the interest in a 1030 nm fs laser over the alternatives. This may also be linked to the point on cell geometry above.

The study uses crater morphology as an indicator of sampling quality, but does not explain why. Some content from L203-205 and the studies referenced on those lines, and content from L232-235 are likely useful here. Regarding the optical data in figure 1, what is the shadow often seen to the right-hand side of the craters, E.g. 1s #221, or 16s #78?

Relating to the statement on L82-83 ‘Crater formation remained broadly stable along the scan paths’ - Figure 1.b appears to show a trend, with more visible rims in craters with a higher index. Also, the rolling mean in fig 2b for the 8s scan increases then flattens, and the ratio for the 16s scan in fig 2c trends upwards. Are there trends here? If so, what could be causing them?

The study does not show downstream coupling to an analytical system; however, a description of how analysis would look in practice would be useful. Discussing an example experimental design using the 96 μm spot size, 0.5 mm pitch, and 1 s exposure (or alternative experimental settings), and how ablated material would be collected and transported from the ambient-air cell would be instructive. This would help interpret the comments on L81 that the 0.5 mm pitch is suitable, and L86 that a 1 s exposure is most suitable for sampling.

L16: Indicate an order of magnitude for the volume of material removed
L27: Specify laser-matter interaction
L45-46: It’s not clear what the 30 cm length ice sections are
L49: The table 1 caption and the data within state 400 positions per exposure time. Figure 1b has white towards the end of the indexes for 1s 2s and 16s. what does the white represent? Were there fewer than 400 measured positions?
The results section contains many short paragraphs, consider combining some for readability. For example, the section starting on L75 could be moved up to before the section starting L72, so the discussion on diameters are placed together
Fig.2a: The y-label would be more understandable as e.g. “Relative frequency” or “Frequency density”
L84: With the trend that lower exposure gives smallest inner diameter, why not test shorter than 1s exposures?
L188: What is the temperature of the jacket?
Citation: https://doi.org/10.5194/egusphere-2026-4182-RC2

Robin Vinther Nielsen, Ioanna Bertsia-Kanatouri, Kerttu Maria Peensoo, Simon Alexander Munk Wael Fassel, Eirini Malegiannaki, and Vasileios Gkinis

Data sets

Supporting data for: Ambient-pressure femtosecond laser ablation as a solid-phase sampling method for water ice Robin Vinther Nielsen et al. https://doi.org/10.5281/zenodo.21099024

Model code and software

LA Crater Analyzer Robin Vinther Nielsen https://github.com/MarsRob/LA_crater_analyzer

Robin Vinther Nielsen, Ioanna Bertsia-Kanatouri, Kerttu Maria Peensoo, Simon Alexander Munk Wael Fassel, Eirini Malegiannaki, and Vasileios Gkinis

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Oct 2026	47	38	7	92
Nov 2026	25	24	2	51

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Short summary

Ice cores can preserve past climate information in layers, but melting or cutting samples for measurements can mix or blur that information. We tested femtosecond laser ablation, a method that removes material with ultrashort laser pulses, to sample ice directly in a cold laboratory. It made repeatable craters less than 0.2 millimeters wide, spaced 0.5 millimeters apart. This could support studies of very old ice cores, where layers are very thin, while leaving most of the sample intact.


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