Open Access
Add to BibSonomy
Abstract
We experimentally study the interaction between intense infrared few-cycle laser pulses and an ultrathin (∼2 µm) flat liquid sheet of isopropanol running in vacuum. We observe a rapid decline in transmission above a critical peak intensity of 50 TW/cm2 of the initially transparent liquid sheet, and the emission of a plume of material. We find both events are due to the creation of a surface plasma and are similar to processes observed in dielectric solids. After calculating the electron density for different laser peak intensities, we find an electron scattering rate of 0.3 fs-1 in liquid isopropanol to be consistent with our data. We study the dynamics of the plasma plume to find the expansion velocity of the plume front.
Published by Optica Publishing Group under the terms of the Creative Commons Attribution 4.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.
1. Introduction
High intensity laser interaction with materials is both rich in physics and applications [1–3]. Laser ablation of solids is used for precision manufacturing of materials and semiconductor devices and to pattern surfaces on a nanometric scale [4] but also to create nanoparticles of dispersed material [5]. This high intensity interaction can also be used to generate plasmas [6], extreme ultraviolet (XUV) high harmonic emission [7–9], localized ultrafast melting [10], and shockwaves [11] in different states of matter. In the biomedical domain further applications are being discovered, with laser surgery a growing tool for precision cauterization, tumor ablation and heating [12,13]. The ultrafast, or femtosecond, laser ablation of a solid surface is well studied [14]. In the femtosecond case, when the deposited energy ionizes the material above the breakdown threshold, the laser pulse leaves a hot dense plasma which expands, often at supersonic velocity. The ionized material is thrown into the vacuum or surrounding atmosphere leaving a pit in the target surface. Repeated laser shots continue this process provided the repetition rate allows for “recovery” and cooling of the system. Similar phenomena are observed in levitated liquid droplets [15,16] or ice crystals [17], but with a modification to the shape and temperature of the ionized volume due to Mie scattering and internal focusing inside the target.
Transparent liquid surfaces or flat sheets have not been widely studied despite their relevance to liquid XUV spectroscopy, self-healing plasma mirrors, remote sensing in liquids and medical laser applications. Moreover, a thin film of liquid can be present at the surface of processed materials and can strongly modify the laser/material interaction. It is expected, but not yet verified, that under an intense laser field an initially transparent liquid system will behave in the same way as a flat surface of a dielectric. The interaction of high intensity laser pulses with a surface is also highly sensitive to the pulse duration and contrast, the wavelength and the material's bandgap or work function [18]. With the growing availability of always shorter few-cycle pulses where the pulse duration is close to one optical cycle, new discoveries are being made with the potential to improve micromachining quality [19] and physics theoretical models [20].
2. Experimental apparatus
In this work, we report and analyze experimental data on the interaction between intense infrared few-cycle laser pulses and an ultrathin transparent liquid sheet in vacuum. The laser system consists of a Ti:Sapphire oscillator seeding a two-stage amplifier (Red Dragon, KM labs and Crunch Technologies) delivering 30 fs, 8 mJ pulses at 1 kHz. This drives an optical parametric amplifier system (HE-TOPAS, Light Conversion) resulting in an idler beam at a wavelength of 1800 nm (35 fs, 1.2 mJ). These pulses are broadened in a hollow core fibre (HCF) filled with 1-2 bars of argon and compressed to the few-cycle regime with adjustable silica wedges [21]. This laser system routinely delivers on target, pulses up to 500 µJ with a pulse duration of 13 fs +/- 2 fs full width at half maximum, which is close to 2 optical cycles at 1800 nm, with a high spatial quality beam profile, a consequence of the spatial filtering of the HCF. The p-polarized pulses are focused by a 50 cm CaF2 lens, mounted on a motorized translation stage, onto an ultrathin liquid sheet placed in a vacuum chamber. The liquid sheet is generated using a bespoke nozzle designed in house and printed and developed using a Nanoscribe 3D printer [22]. Internally, the nozzle collides liquid streams at a specific angle leading to an ultrathin acute leaf shaped laminar flow. In this study we use isopropanol (IPA) to take advantage of the low surface tension and vapor pressure that eases the delivery of a well-behaved liquid sheet in a vacuum environment. The liquid sheet thickness was measured with monochromatic and white-light interferometry. At a distance of 3 to 5 mm from the nozzle, where the laser hits the liquid sheet, the thickness is varying from 2.3 to 1.7 µm [22]. As the liquid flows at a speed of 14 m/s, each laser shot hits a fresh liquid surface. The liquid sheet can be rotated to modify the angle of incidence of the laser beam. The residual liquid is then captured in a collector. The liquid delivery system is surrounded by a cold trap filled with liquid nitrogen to keep the vacuum level at ∼10−4 mbar.
We investigate the laser/liquid interaction with 2 cameras (Fig. 1). The first camera is an ultrafast camera (Phantom v7.3, Vision Research, 100,000 fps) looking at the laser/liquid interaction zone through a side viewport. The second charge-coupled device (CCD) camera records images of the beam profile, after the jet, to study the transmission of the laser through the liquid. The beam is attenuated before the camera with neutral density filters. The values reported here are peak intensities and peak fluences of Gaussian beams considering the losses in the different optics and the temporal pedestals common in few-cycle laser pulses [23].
Fig. 1. (a) Few-cycle infrared laser pulses are focused onto a ∼2 µm thick flat sheet of liquid running in vacuum. Transmission through the liquid sheet is monitored with a CCD camera. An ultrafast camera observes through a side-viewport to the laser-liquid interaction zone. (b) Side view of the jet when laser peak intensity < 50 TW/cm2. (c) Side view of the jet when laser peak intensity > 50 TW/cm2, where a plasma plume is visible on the front side of the liquid sheet (laser pulse coming from the left). (d) Front view of the ultrathin flat liquid sheet without laser irradiation.
3. Laser/liquid interaction at high intensity
Here we present results on the interaction between the laser pulses and the liquid sheet while varying the laser peak intensity. The peak intensity is changed by moving the motorized lens, thus modifying the interaction spot size on target while keeping the same pulse energy and duration. The spot size was calculated using standard formulas for focusing of Gaussian beams and corrections to the focus radius when using an iris. The spot size was checked by imaging the beam at the focus, i.e., at the liquid jet, and measuring its size. The intensity measure was further cross-checked with the high harmonic generation cut-off law in gas presented in [9] and the uncertainty is estimated to be +/- 5 TW/cm2.
The first noticeable effect on the liquid jet when varying the intensity is the appearance of a plasma plume on the front side of the sheet when the peak intensity exceeds 50 TW/cm2 (peak fluence of 0.7 J/cm2 with 13 fs pulses; focus radius of 113 µm at 1/e2), Fig. 1(c). This plasma plume is a sign of the breakdown of the material at high intensity. Breakdown thresholds of around 3 TW/cm2 have been previously reported for liquid water for 340-fs long infrared pulses [24] and between 16 and 25 TW/cm2 for liquid water [25–27] and liquid ethanol [27] when ∼150-fs long infrared pulses are used. The higher breakdown threshold reported here can be explained by the use of few-cycle pulses. It has been shown in [20,28] that the use of shorter laser pulses increases the damage threshold of materials. In the infrared, the wavelength of the laser has a limited impact on the breakdown threshold value and the mechanism is not yet fully understood for ultrashort pulses [18,29,30].
A second effect, when exceeding 50 TW/cm2, is a strong lack of transmission of the initially transparent liquid sheet, shown in Fig. 2(a). The transmission through the liquid sheet is monitored with a CCD camera by comparing the profile of the beam when the liquid jet is running or not. The diagnostic is spatially integrated, so that the intensity variation does not affect the transmission results. As the camera is imaging a 2nd order process (2-photon absorption, 1800 nm beam on a silicon sensor), a square root deconvolution is applied to the results. Here the laser beam hits the liquid sheet with an angle of incidence of 40°. The lack of transmission, another sign of the breakdown of the material, is explained by a strong absorption and/or reflection by the liquid [27].
Fig. 2. (a) Comparison of the experimental transmission with the theoretical model, see Eqs. (2) and (3). Insets: images of the transmitted beam profile at two different on-target peak intensities. (b) Electron density in a 2-µm thick liquid sheet surrounded by vapor (blue line and area; right axis, logarithmic scale) calculated with a 3D propagation code for different laser peak intensities. The laser pulse passes through the liquid sheet from left to right. On the front side, the electron density exceeds the critical density above 50 TW/cm2.
Here we study a theoretical model to explain this strong modification of the transmission. First, the transmission of the liquid sheet is directly linked to the ionization level of the material [20], thus we investigate the electron density in the liquid with a 3D propagation model described in detail in [31]. The liquid is modelled as a flat sheet of dense media matching the neutral density of liquid isopropanol with an abrupt Lorentzian decay to vapor pressure on the front and rear sides, see Fig. 2(b). We set the liquid thickness to 2 µm to match the experimentally measured value [22]. The pulse, with the same parameters as the experiment, propagates using the forward Maxwell equation in 3 dimensions with cylindrical symmetry. Instantaneous ionization rates are calculated using the ADK formula [32]. The pulse is too short for considering avalanche ionization [33]. The ionization potential (Ip) of the isopropanol molecule is estimated to be 10.3 eV [34]. The integration is performed using a preconditioned Runge-Kutta method with adaptive step-sizing. Nonlinear effects are applied in the real-space domain while dispersion and diffraction are applied in the frequency domain (Split-step method).
Figure 2(b) presents the calculated electron density within the liquid sheet for different laser intensities. On the front surface of the liquid, when the laser peak intensity is above 50 TW/cm2, the electron density exceeds the critical density, nc = 3.4 × 1020 cm-3 in our case, Eq. (1).
Thus, the plasma frequency exceeds the laser frequency and leads to a strong reflection of the laser pulse by the plasma [35], reproducing our experimental results. An offset of -4 TW/cm2 must be applied to numerical results for best agreement with the experiment. This offset may be due to the difficulty of measuring precisely the experimental peak intensity (focal spot size or pulse duration errors) and/or to the lack of precision of the numerical model.
In metallic and dielectric media, the reflectivity, R, here for p-polarization, can be modelled by the Fresnel reflection formula (Eq. (2)) coupled to the Drude theory which gives the dielectric function, ɛ, as a function of the plasma frequency, ωp (Eq. (2b)). The plasma frequency is directly linked to the electron density, ne, Eq. (2c) [35]. θ is the angle of incidence (here 40°), ωl is the laser frequency, n0 the complex refractive index of isopropanol at 1800 nm [36], me the electron rest mass, ɛ0 the vacuum permittivity, e the elementary charge and v the electron scattering rate.
The absorption, A, occurring in the liquid and leading to the ionization of the material, is simply modelled by the loss of ∼15 photons to ionise 1 neutral isopropanol molecule in the plasma volume V, Eq. (3). At these intensities (< 80 TW/cm2), we anticipate only low order above-threshold ionization so the mean energy in the electron kinetic energy distribution will remain close to the value obtained by one excess photon [37]. Thus, we estimate that the liberated free electron has the same energy as the laser photon energy El (0.7 eV). Ne is the total number of liberated electrons, Ne = Vne.
We apply Eqs. (2) and (3) to the electron densities calculated at the front surface, where the plasma has a major effect on the transmission, with the electron scattering rate as a free parameter. We find an excellent agreement between this model and experimental results for an electron scattering rate v = 0.3 fs-1, see Fig. 2(a). This value is in agreement with the results reported in [33,38]. In [33], Feit et al. estimated this value to be about 3 times lower in liquid water than in solid glass by comparing experimental femtosecond-laser damage thresholds in these materials (1 fs-1 in solid glass). In [38], Dubietis et al. found a value of 0.33 fs-1 to be in agreement with their study of laser filamentation in liquid water. The electron scattering rate is dependent on both electron temperature and density [33]. For simplicity, we used a fixed electron scattering rate over the electron density range used in our study.
The lack of transmission of the liquid at high intensity observed here is therefore explained by a strong reflectivity of the front surface when the ionization exceeds the critical density. In our experiment, where a few-cycle long-wavelength laser is focused on a target with a weak electron scattering rate, a small amount of absorption leads to a strong reflectivity of the material (Fig. 3). This has strong implication on high harmonic generation (HHG) in dense media where the XUV radiation is generated near the rear surface of the material. The high intensity required to initiate the highly non-linear HHG process can be strongly reflected off the front surface, clamping the HHG efficiency [9]. On the other hand, this capacity could be of great interest for plasma mirrors (PM) or optically-driven shutter systems when coupled with the extremely flat, damage-free, flowing liquid system [39–43].
Fig. 3. Calculated plasma reflectivity as a function of electron density for different laser wavelengths and electron scattering rates, calculated with the Fresnel and Drude equations, Eq. (2).
4. Plasma plume expansion dynamics
The reflection/absorption of the optical field energy is one part of the physical interaction, the other is the mass flow induced by the interaction in the liquid monitored by an observable plume emission. In Fig. 2(b), the laser absorption in the liquid reaches a value of around 5% at 50 TW/cm2 which corresponds to around 10 uJ of energy absorbed in the focal volume at the front surface of the liquid. This amount of energy, localized in a small volume, is equivalent to a pressure that is greater than the bulk modulus of isopropanol: 1.07 GPa. Thus, a shockwave is created for intensities above this threshold. The ionized material expands and is therefore thrown into the surrounding vacuum, leading to the appearance of the plasma plume as seen in Fig. 1(c).
Figure 4 presents different results obtained with the ultrafast camera at a peak intensity of 70 TW/cm2. The plasma plume is observable due to the fluorescent decay of the hot expelled particles. The recording system used here is not optimal for imaging such fast events as the minimal integration time is longer than the duration of the event. Nevertheless, we are reporting, to the best of our knowledge, the first ultrafast observation of a plasma plume from a liquid sheet. In Figs. 4(b) and (c) are presented an image and a lineout of the complete plasma plume self-emission propagating backward compared to the laser pulse. No signal is recorded from the rear side of the liquid sheet. The pulse is sufficiently attenuated by the plasma reflectivity at the front surface to avoid complete destruction of the liquid sheet by the laser pulse. The ultrafast camera used in our experiment has a minimum exposure time of 1 µs, so we are unable to measure the evolution of a single plume directly. We overcome this issue by delaying the camera trigger between the regularly produced plumes created by consecutive pulses of the 1 kHz laser train. After analysis of this data, we can extract a plume front velocity of around 21,000 m/s, see Fig. 4(d). With our system, the plume self-emission is detectable for 334 ns +/- 84 ns. These values are in agreement with plasma plumes created from dielectric solids [44] and as with dielectric solids, and contrary to metals, we do not observe a second “slow” nanoparticles plume [44] as the nanoparticles may not be fluorescent and thus not observable with our system. Finer results could be obtained in the future with an improved ultrafast imaging system, leading to a better understanding of the behavior of plasma plumes from liquid targets.
Fig. 4. (a) Time framed side-view of the liquid jet (dashed blue line) before the laser pulse (orange arrow) hits the liquid. The background signal is the ambient light reflected by the jet. (b) Side view of the liquid jet after the pulse hits the jet with a peak intensity of 70 TW/cm2. Integration time is 23 µs and the angle of incidence is 0°. A plasma plume is emitted in the reverse direction of the laser. (c) Axial lineout of the plasma plume. (d) Position of the plume self-emission front at different points in time. The time uncertainty is +/- 25% and is explained by the long camera exposure compared to the duration of the event. Dashed line: theoretical plume front position for a constant speed of 21,000 m/s.
The ablated volume is estimated considering 90% of the absorbed laser energy is transformed into kinetic energy [45]. With 34 uJ absorbed in the front surface of the liquid (at 70 TW/cm2) and an expansion velocity of 21,000 m/s, we can estimate an ablated mass of 1.4 × 10−13 kg which corresponds to a volume of 178 µm3 for isopropanol. The ablation efficiency is then about 0.6 µm3/µJ and agrees with values reported for solid dielectrics near the damage threshold (0.4 - 0.7 µm3/µJ) when machined by few-cycle laser pulses [46].
5. Conclusion and prospects
We have shown that the interaction between few-cycle laser pulses and an ultrathin sheet of transparent liquid is very similar to the interaction between laser pulses and solid dielectric surfaces. We report a breakdown threshold of 50 TW/cm2 for liquid isopropanol when illuminated with 1800 nm few-cycle pulses. Above this threshold, a lack of transmission of the initially transparent material is observed and is explained by the strong reflectivity of the plasma created at the front surface. An electron scattering rate of 0.3 fs-1 is found for liquid isopropanol under intense ultrashort laser excitation. A direct measurement of the reflected energy would confirm this model. A plasma plume is also observed above this threshold. We studied the expansion dynamics of this plume self-emission with an ultrafast camera, and we observed a similar behavior to that of plasma plumes from solid dielectrics. This work will lead to a better understanding of the behavior of liquid sheets under intense laser fields which is of prime interest for XUV generation in liquids [8,9], plasma mirrors or plasma shutters [40,41], proton acceleration [47], hydrogel micro-machining [25] and laser surgery, where a thin liquid film is usually present on tissue surfaces [48].
Funding
Royal Society (URF/R1/191759); Marie Curie (641272); Defence Science and Technology Laboratory (MURI EP/N018680/1); Engineering and Physical Sciences Research Council (EP/N018680/1, EP/R019509/1).
Acknowledgments
We gratefully acknowledge input and advice from Dane Austin in the simulations, fruitful discussion with Roland Smith, technical help from Andy Gregory and Susan Parker in the construction of the apparatus, and advice and loan of the ultrafast camera from the Institute of Shock Physics, Imperial College London.
Disclosures
The authors declare no conflicts of interest.
Data availability
Data underlying the results presented in this paper are not publicly available at this time but may be obtained from the authors upon reasonable request.
References
1. C. J. Joshi and P. B. Corkum, “Interactions of ultra-intense laser light with matter,” Phys. Today 48(1), 36 (1995). [CrossRef]
2. S. L. Chin, S. A. Hosseini, W. Liu, Q. Luo, F. Théberge, N. Aközbek, A. Becker, V. P. Kandidov, O. G. Kosareva, and H. Schroeder, “The propagation of powerful femtosecond laser pulses in opticalmedia: physics, applications, and new challenges,” Can. J. Phys. 83(9), 863–905 (2005). [CrossRef]
3. M. V. Shugaev, C. Wu, O. Armbruster, A. Naghilou, N. Brouwer, D. S. Ivanov, T. J.-Y. Derrien, N. M. Bulgakova, W. Kautek, B. Rethfeld, and L. V. Zhigilei, “Fundamentals of ultrafast laser–material interaction,” MRS Bull. 41(12), 960–968 (2016). [CrossRef]
4. L. Orazi, L. Romoli, M. Schmidt, and L. Li, “Ultrafast laser manufacturing: from physics to industrial applications,” CIRP Ann. 70(2), 543–566 (2021). [CrossRef]
5. M. Kim, S. Osone, T. Kim, H. Higashi, and T. Seto, “Synthesis of Nanoparticles by Laser Ablation: A Review,” KONA 34(0), 80–90 (2017). [CrossRef]
6. D. Umstadter, “Review of physics and applications of relativistic plasmas driven by ultra-intense lasers,” Phys. Plasmas 8(5), 1774–1785 (2001). [CrossRef]
7. S. Ghimire and D. A. Reis, “High-harmonic generation from solids,” Nat. Phys. 15(1), 10–16 (2019). [CrossRef]
8. T. T. Luu, Z. Yin, A. Jain, T. Gaumnitz, Y. Pertot, J. Ma, and H. J. Wörner, “Extreme–ultraviolet high–harmonic generation in liquids,” Nat. Commun. 9(1), 3723 (2018). [CrossRef]
9. O. Alexander, J. C. T. Barnard, E. W. Larsen, T. Avni, S. Jarosch, C. Ferchaud, A. Gregory, S. Parker, G. Galinis, A. Tofful, D. Garratt, M. R. Matthews, and J. P. Marangos, “The mechanism of high harmonic generation in liquid alcohol,” arXiv:2202.12624 (2022).
10. N. K. Kulachenkov, S. Bruyere, S. A. Sapchenko, Y. A. Mezenov, D. Sun, A. A. Krasilin, A. Nominé, J. Ghanbaja, T. Belmonte, V. P. Fedin, E. A. Pidko, and V. A. Milichko, “Ultrafast Melting of Metal–Organic Frameworks for Advanced Nanophotonics,” Adv. Funct. Mater. 30(7), 1908292 (2020). [CrossRef]
11. V. E. Fortov, “Intense shock waves and extreme states of matter,” Phys.-Usp. 50(4), 333–353 (2007). [CrossRef]
12. S. H. Chung and E. Mazur, “Surgical applications of femtosecond lasers,” J. Biophotonics 2(10), 557–572 (2009). [CrossRef]
13. K. Plamann, F. Aptel, C. L. Arnold, A. Courjaud, C. Crotti, F. Deloison, F. Druon, P. Georges, M. Hanna, J.-M. Legeais, F. Morin, É Mottay, V. Nuzzo, D. A. Peyrot, and M. Savoldelli, “Ultrashort pulse laser surgery of the cornea and the sclera,” J. Opt. 12(8), 084002 (2010). [CrossRef]
14. E. G. Gamaly, A. V. Rode, B. Luther-Davies, and V. T. Tikhonchuk, “Ablation of solids by femtosecond lasers: Ablation mechanism and ablation thresholds for metals and dielectrics,” Phys. Plasmas 9(3), 949–957 (2002). [CrossRef]
15. P. V. Bulat, O. P. Minin, and K. N. Volkov, “Numerical simulation of optical breakdown in a liquid droplet induced by a laser pulse,” Acta Astronaut. 150, 162–171 (2018). [CrossRef]
16. S. Yu. Grigoryev, B. V. Lakatosh, M. S. Krivokorytov, V. V. Zhakhovsky, S. A. Dyachkov, D. K. Ilnitsky, K. P. Migdal, N. A. Inogamov, A. Yu. Vinokhodov, V. O. Kompanets, Yu. V. Sidelnikov, V. M. Krivtsun, K. N. Koshelev, and V. V. Medvedev, “Expansion and Fragmentation of a Liquid-Metal Droplet by a Short Laser Pulse,” Phys. Rev. Applied 10(6), 064009 (2018). [CrossRef]
17. M. Matthews, F. S. Pomel, C. Wender, A. Kiselev, D. Duft, J. Kasparian, J.-P. Wolf, and T. Leisner, “Laser vaporization of cirrus-like ice particles with secondary ice multiplication,” Sci. Adv. 2(5), e1501912 (2016). [CrossRef]
18. L. Gallais, D.-B. Douti, M. Commandré, G. Batavičiūtė, E. Pupka, M. Ščiuka, L. Smalakys, V. Sirutkaitis, and A. Melninkaitis, “Wavelength dependence of femtosecond laser-induced damage threshold of optical materials,” J. Appl. Phys. 117(22), 223103 (2015). [CrossRef]
19. N. Sanner, O. Utéza, B. Chimier, M. Sentis, P. Lassonde, F. Légaré, and J. C. Kieffer, “Toward determinism in surface damaging of dielectrics using few-cycle laser pulses,” Appl. Phys. Lett. 96(7), 071111 (2010). [CrossRef]
20. P. A. Zhokhov and A. M. Zheltikov, “Optical breakdown of solids by few-cycle laser pulses,” Sci Rep 8(1), 1824 (2018). [CrossRef]
21. D. R. Austin, T. Witting, S. J. Weber, P. Ye, T. Siegel, P. Matía-Hernando, A. S. Johnson, J. W. G. Tisch, and J. P. Marangos, “Spatio-temporal characterization of intense few-cycle 2 µm pulses,” Opt. Express 24(21), 24786 (2016). [CrossRef]
22. G. Galinis, J. Strucka, J. C. T. Barnard, A. Braun, R. A. Smith, and J. P. Marangos, “Micrometer-thickness liquid sheet jets flowing in vacuum,” Rev. Sci. Instrum. 88(8), 083117 (2017). [CrossRef]
23. C. Brahms, F. Belli, and J. C. Travers, “Infrared attosecond field transients and UV to IR few-femtosecond pulses generated by high-energy soliton self-compression,” Phys. Rev. Research 2(4), 043037 (2020). [CrossRef]
24. A. Vogel, N. Linz, S. Freidank, and G. Paltauf, “Femtosecond-Laser-Induced Nanocavitation in Water: Implications for Optical Breakdown Threshold and Cell Surgery,” Phys. Rev. Lett. 100(3), 038102 (2008). [CrossRef]
25. J. Hernandez-Rueda, D. Baasanjav, A. P. Mosk, and D. van Oosten, “Femtosecond laser-ablation of gel and water,” Opt. Lett. 45(11), 3079 (2020). [CrossRef]
26. B.-M. Kim, A. M. Komashko, A. M. Rubenchik, M. D. Feit, S. Reidt, L. B. D. Silva, and J. Eichler, “Interferometric analysis of ultrashort pulse laser-induced pressure waves in water,” J. Appl. Phys. 94(1), 709–715 (2003). [CrossRef]
27. E. Ponomareva, A. Ismagilov, S. Putilin, and A. N. Tcypkin, “Plasma reflectivity behavior under strong subpicosecond excitation of liquids,” APL Photonics 6(12), 126101 (2021). [CrossRef]
28. I. Mirza, N. M. Bulgakova, J. Tomáštík, V. Michálek, O. Haderka, L. Fekete, and T. Mocek, “Ultrashort pulse laser ablation of dielectrics: Thresholds, mechanisms, role of breakdown,” Sci. Rep. 6(1), 39133 (2016). [CrossRef]
29. N. Linz, S. Freidank, X.-X. Liang, and A. Vogel, “Wavelength dependence of femtosecond laser-induced breakdown in water and implications for laser surgery,” Phys. Rev. B 94(2), 024113 (2016). [CrossRef]
30. E. Migal, E. Mareev, E. Smetanina, G. Duchateau, and F. Potemkin, “Role of wavelength in photocarrier absorption and plasma formation threshold under excitation of dielectrics by high-intensity laser field tunable from visible to mid-IR,” Sci. Rep. 10(1), 14007 (2020). [CrossRef]
31. A. S. Johnson, D. R. Austin, D. A. Wood, C. Brahms, A. Gregory, K. B. Holzner, S. Jarosch, E. W. Larsen, S. Parker, C. S. Strüber, P. Ye, J. W. G. Tisch, and J. P. Marangos, “High-flux soft x-ray harmonic generation from ionization-shaped few-cycle laser pulses,” Sci. Adv. 4(5), eaar3761 (2018). [CrossRef]
32. V. S. Popov, “Tunnel and multiphoton ionization of atoms and ions in a strong laser field (Keldysh theory),” Phys.-Usp. 47(9), 855–885 (2004). [CrossRef]
33. M. D. Feit, A. M. Komashko, and A. M. Rubenchik, “Ultra-short pulse laser interaction with transparent dielectrics,” Appl. Phys. A: Mater. Sci. Process. 79(7), 1657–1661 (2004). [CrossRef]
34. B. J. Cocksey, J. H. D. Eland, and C. J. Danby, “The effect of alkyl substitution on ionisation potential,” J. Chem. Soc. B, 790–792 (1971). [CrossRef]
35. M. Lebugle, N. Sanner, S. Pierrot, and O. Utéza, “Absorption dynamics of a femtosecond laser pulse at the surface of dielectrics,” in AIP Conference Proceedings1464 (2012), pp. 91–101.
36. T. L. Myers, R. G. Tonkyn, T. O. Danby, M. S. Taubman, B. E. Bernacki, J. C. Birnbaum, S. W. Sharpe, and T. J. Johnson, “Accurate Measurement of the Optical Constants n and k for a Series of 57 Inorganic and Organic Liquids for Optical Modeling and Detection,” Appl. Spectrosc. 72(4), 535–550 (2018). [CrossRef]
37. B. Schütte, C. Peltz, D. R. Austin, C. Strüber, P. Ye, A. Rouzée, M. J. J. Vrakking, N. Golubev, A. I. Kuleff, T. Fennel, and J. P. Marangos, “Low-Energy Electron Emission in the Strong-Field Ionization of Rare Gas Clusters,” Phys. Rev. Lett. 121(6), 063202 (2018). [CrossRef]
38. A. Dubietis, A. Couairon, E. Kučinskas, G. Tamošauskas, E. Gaižauskas, D. Faccio, and P. Di Trapani, “Measurement and calculation of nonlinear absorption associated with femtosecond filaments in water,” Appl. Phys. B 84(3), 439–446 (2006). [CrossRef]
39. S. Backus, H. C. Kapteyn, M. M. Murnane, D. M. Gold, H. Nathel, and W. White, “Prepulse suppression for high-energy ultrashort pulses using self-induced plasma shuttering from a fluid target,” Opt. Lett. 18(2), 134–136 (1993). [CrossRef]
40. B. H. Shaw, S. Steinke, J. van Tilborg, and W. P. Leemans, “Reflectance characterization of tape-based plasma mirrors,” Phys. Plasmas 23(6), 063118 (2016). [CrossRef]
41. G. Doumy, F. Quéré, O. Gobert, M. Perdrix, P. H. Martin, P. Audebert, J. C. Gauthier, J.-P. Geindre, and T. Wittmann, “Complete characterization of a plasma mirror for the production of high-contrast ultraintense laser pulses,” Phys. Rev. E 69(2), 026402 (2004). [CrossRef]
42. D. Panasenko, A. J. Shu, A. Gonsalves, K. Nakamura, N. H. Matlis, C. Toth, and W. P. Leemans, “Demonstration of a plasma mirror based on a laminar flow water film,” J. Appl. Phys. 108(4), 044913 (2010). [CrossRef]
43. C. I. D. Underwood, G. Gan, Z.-H. He, C. D. Murphy, A. G. R. Thomas, K. Krushelnick, and J. Nees, “Characterization of flowing liquid films as a regenerating plasma mirror for high repetition-rate laser contrast enhancement,” Laser Part. Beams 38(2), 128–134 (2020). [CrossRef]
44. E. Axente, S. Noël, J. Hermann, M. Sentis, and I. N. Mihailescu, “Subpicosecond laser ablation of copper and fused silica: Initiation threshold and plasma expansion,” Appl. Surf. Sci. 255(24), 9734–9737 (2009). [CrossRef]
45. N. Varkentina, N. Sanner, M. Lebugle, M. Sentis, and O. Utéza, “Absorption of a single 500 fs laser pulse at the surface of fused silica: Energy balance and ablation efficiency,” J. Appl. Phys. 114(17), 173105 (2013). [CrossRef]
46. M. Lebugle, N. Sanner, O. Utéza, and M. Sentis, “Guidelines for efficient direct ablation of dielectrics with single femtosecond pulses,” Appl. Phys. A 114(1), 129–142 (2014). [CrossRef]
47. J. T. Morrison, S. Feister, K. D. Frische, D. R. Austin, G. K. Ngirmang, N. R. Murphy, C. Orban, E. A. Chowdhury, and W. M. Roquemore, “MeV proton acceleration at kHz repetition rate from ultra-intense laser liquid interaction,” New J. Phys. 20(2), 022001 (2018). [CrossRef]
48. L. Hoffart, P. Lassonde, F. Légaré, F. Vidal, N. Sanner, O. Utéza, M. Sentis, J.-C. Kieffer, and I. Brunette, “Surface ablation of corneal stroma with few-cycle laser pulses at 800 nm,” Opt. Express 19(1), 230 (2011). [CrossRef]
